Tag Archives: sdl 2.0

Android, SDL2 and Pascal?

Recently, I get more and more questions and requests regarding the development of Android applications with SDL2 and Free Pascal. Since I’m not planning to do a tutorial chapter on this in the near future, I would like to share some resources which may help you to set your system up. – Contact me, if you are interested in sharing a tutorial on how to set up a SDL2/Free Pascal/Android development environment (or if you know further resources which should be covered here).

  1. This step by step tutorial describes very detailed the setup of a SDL2/Android development environment under Window, though it aims for C++ development rather than Pascal development: 


  1.  This is a short introduction how to setup your system and Lazarus (Free Pascal) to develop Android Apps:


  1. These links lead you to a Lazarus package that allows for SDL2 and simple Android development and a configuration of it:





Chapter 2 – Installation and Configuration (Linux version)

This chapter illustrates quickly how to get an environment for Free Pascal/SDL2 development running under Linux. Attention: The following instruction may work for many Debian and Ubuntu based Linux distributions, others probably need different installation procedures.

In contrast to the Windows, in Linux there are so many variables according to the operation system (thousands of different distributions) that there can’t be a more or less generalized way how to install it. Anyway I’d like to demonstrate how it worked for me and give some hints which may help you to install it to your favorite distribution of Linux.

The distribution and software I used:

  • Linux Distribution: Linux Mint 17.2 (Ubuntu/Debian based)
  • Desktop: Cinnamon Desktop
  • Lazarus 1.6 (installed from .deb file)
  • FPC 3.0.0 (installed from .deb file)
  • FPC 3.0.0 Source Code (installed from .deb file)
  • Tim Blume’s SDL2 units (header translation)
  • SDL2, SDL2_image, SDL2_ttf dynamic library files (Linux has .so files instead of .dll files)

Download and install FPC, FPC sourc code and Lazarus

The first step is to install the Free Pascal compiler (version 3.0.0 or higher), the Compiler’s source code (same version as the compiler) and the Lazarurs IDE (version 1.6 or higher). First check if your package manager provides this software in these (or higher) versions! It is likely that you find the software but the versions may lack behind. If that is the case, download and execute these three .deb files in the shown sequence.

Again Careful: These files are right for many Debian and Ubuntu based distributions (like Linux Mint) but may be wrong for others. Try to find out the right ones for your Linux.

  • fpc_3.0.0-151205_amd64.deb
  • fpc-src_3.0.0-151205_amd64.deb
  • lazarus_1.6-0_amd64.deb
  • Download source: http://lazarus-ide.org (find the download button)
Install Packages for Linux FPC SDL2 environment with Lazarus
SourceForge download page for all three files necessary (accessed via Download button at lazarus-ide.org). The original description is kept in the image.


If everything went right, Lazarus can be started up by typing “startlazarus” in the terminal or by finding the program here: /usr/bin/startlazarus which is a symbolic link to the actual executable here: /usr/share/lazarus/1.6/startlazarus. On your system it may be located at a different location but these are rather standard location.

Start up Lazarus

On start up of Lazarus the directories for FPC and the FPC source code were found and set already. As a hint I show where these are located on my system are:

  • FPC: /usr/bin/fpc
  • FPC Source code: /usr/share/fpcsrc/3.0.0 (because $(FPCVER) equals the version number, see screenshot)
Path FPC and FPC Source code
Either detected automatically or can be manually added by Tools > Options …

Before proceeding, my suggestion is to start a new project (simple program) and try out if you are able to do a simple compilation of a very simple program. E.g. a simple writeln-statement.

As a tip you should open up Lazarus’ Console to see the output of your program and writeln commands. You can find the Console at Window > Console.

Get the SDL2 units

Get the latest version of the translated SDL2 units.

Download SDL2 units on GitHub
Choose the master branch (1), click on “Clone or download” (2) and click on Download ZIP (3).

Make sure you have the master branch chosen and then click on “Clone or download”, then “Download ZIP”.

After extracting the ZIP file I suggest to rename the new folder into “sdl2” or “SDL2” and place it at this location:

  • /usr/local/share/
  • SDL2 units are then here: /usr/local/share/sdl2
Path to SDL2 units
This folder is suggested as a place for the SDL2 units. By the way, “Chap7” is just a random name for this project and you may have anything else there instead (I was trying out Chapter 7 tutorial code).

To copy the folder to /usr/local/share/ you usually need root permission. Also make sure the new folder allows for access to its files. In my case I had to make sure that the “root group” has access to files.

Get the SDL2 dynamic library

If you are looking for the most recent pre-compiled SDL2 dynamic link library files (e.g. libSDL2.so) on the official SDL2 website, you just find a remark that reads like this:

Please contact your distribution maintainer for updates.

Since SDL2 is very widespread it is very likely that you distribution maintainer already included the files.

Find SDL2 and all necessary libraries in your distribution’s package manager. Perhaps you have a search field as shown (upper right arrow). The screenshot shows what could come up then:

SDL2 in package manager
Installation of the SDL2 dynamic link libraries in Linux via the package manager.

As you can see, for me at this moment the SDL2 dynamic link library, version 2.0.0 (libsdl2-2.0.0) was already installed (the small green check mark indicates this in Linux Mint). Anyway, SDL2_gfx (libsdl2-gfx-1.0.0) and SDL2_image (libsdl2-image-2.0.0)  weren’t installed.

Find all necessary libraries and install them. These you should install:

  • SDL2
  • SDL2_image
  • SDL2_ttf
  • SDL2_mixer

At least for my tutorials SDL2_gfx is not necessary but you may try it out.

The version of these libraries does not necessarily need to be the most recent unfortunately. If you really need the most recent versions here, you may try to contact the maintainer to ask to update the version.

That’s it :-)!…. – Unfortunately I ran into troubles…

The linker doesn’t find libSDL2.so

So, what I got when I tried to run the basic SDL2 code from Chapter 3:

  • /usr/bin/ld: cannot find -lSDL2

Linker error message

Although I installed the SDL2 dynamic link library I get the linker saying it cannot find it. When looking for sdl2 in /usr/lib and its sub-folders where dynamic link libraries are placed usually, I got these two files:

  • libSDL2-2.0.so.0 (which is a symbolic link to the file below)
  • libSDL2-2.0.so.0.2.0 (this is the correct file!)

Anyway, the linker expects libSDL2.so, so what can you do? – Create a symbolic link with that name. This is done in the Terminal by:

Create a symbolic link to libSDL2.so

  • locate SDL2: shows where SDL2 is located and how it is named (for me they were in /usr/lib/x86_64-linux-gnu)
  • sudo ln -s [destination of symbolic link] [name of the symbolic link]
  • sudo requires to enter the root permission password

Repeat the same for all libraries (SDL2_image, … and so on) you want to use.

Congratulation! After that, everything should run smoothly :-)! I tried chapter 3-9 and all worked well for me.

Linux specific experiences

Launching application invalid

On opening up a Lazarus project (.lpi file) and try to re-run it, I get an error window titled “Launching application invalid” which said “The launching application “”[full path including the execution file of the project]”” does not exist or is not executable.” and further “See Run -> Run parameters -> Local“.

Not sure why this is. Anyway, deleting the executable from the project folder or compiling the project before running it, fixes this issue.

← Chapter 1 | Chapter 3 →

OpenGL Logo

SDL 2.0 meets modern OpenGL

Good news, Chapter 10 has been released right now! You ever wondered what to do if you would like to create 3d graphics for a game or application? – Well, you go for modern OpenGL. And SDL 2.0 is probably the best and most convenient way to go for modern OpenGL nowadays, even professionals typically use SDL as powerful assistant for their OpenGL applications.  Learn more about the strong relationship between SDL and OpenGL in Chapter 10. – And learn how it’s done, of course ;-).

Chapter 3 got a short explanation now on how to copy the source code of a chapter. In the SDL 1.2 chapters the source code  was shipped for each chapter as Pascal file. Nowadays it is much more convenient to grab the source code (or just the desired parts) by copying it directly from the chapter’s source code boxes (in the browser) and paste it whereever it is needed.

The transfer of the old website has been finished. Nearly the complete content is in some way or another transfered to the new page. For example, all tutorial pages (even the old ones) are still available. Some downloads are integrated at the corresponding tutorial pages now, so they are not lost. Some pages are gone, these are Downloads, Tables and Links. These pages are of no benefit anymore since their information are now provided at the corresponding place instead of separate pages. Nevertheless, links trying to access these pages are redirected to the main page to prevent broken links.

No One’s Space got greenlit. This means that this Free Pascal/SDL game will be available in Steam for purchase soon. It demonstrates the power of Free Pascal and SDL.

Small update of some subdomain settings. Subdomain links work again.

Chapter 10 – SDL and modern OpenGL 3.0+

This chapter will introduce you on how to combine the SDL library with the famous Open Graphics Library (OpenGL).

What is OpenGL?

OpenGL is the first choice when it comes to platform independent 2d and 3d graphics programming. The emphasis is on graphics programming only though!

Why and when to combine SDL and OpenGL?

SDL is an excellent choice if you need platform independent 2d graphics. OpenGL is capable of 2d graphics, too, but why using the more complicated library if you could use the easy to use SDL library? – And by the way, underneath SDL is actually using OpenGL (or similar libraries depending upon the system) to achieve its hardware accelerated 2d graphics.

However, if your project needs 3d graphics, which isn’t covered by SDL, you can set up your system for this quite easy with SDL. The setup of an OpenGL environment is very easy and platform independent with SDL. Without SDL you would’ve to write different code to set up OpenGL for each operating system. In fact, even professional developers use SDL to set up their OpenGL applications.

Furthermore, since OpenGL is a pure graphics library, any other task is further done by SDL (e.g. keyboard handling, sound,…).

At this point I’d like to quote Klaus Vor der Landwehr (professional developer) from Turtle-Games, who described the relation of SDL and OpenGL in a very clear way.

Although the graphics are often in the foreground, it is for me as a game programmer only one aspect of many with which I have to deal. And the graphics do not even require the most work. OpenAL for example costs much more time and effort if you want to build a 3D sound channel management. And there are many other interfaces. Here is a list of categories in which SDL has been a great help:

  • multiple displays
  • window management
  • Event handling
  • keyboard
  • mouse
  • joystick
  • game controller
  • force feedback
  • threads
  • timers

… for Windows, Mac and Linux.

Source: Pascal Game Development Community.

What exactly is modern OpenGL?

As of version 2.0 of OpenGL, the so-called fixed pipeline has been replaced by a programmable pipeline (modern OpenGL). In general, the pipeline makes your input data appear on the screen in a hardware accelerated manner by using your graphics card. For the fixed pipeline it was easy to draw something to the screen but, as the name suggests, it was quite fixed and unflexible. The programmable pipeline which is controlled by a newly introduced shader (script) language is far more flexible, though, the ease is gone :-D.

Anyway, some people refer to OpenGL version 3.0 and up as modern OpenGL. This is because a lot of typical functionality was deprecated as of this version. The backwards compatibility is gone.

In this chapter I will demonstrate how to use SDL 3.0 and up to set up a modern OpenGL environment using some basic shaders. I based the description heavily on an excellent C++ tutorial over at opengl-tutorial.org and their second chapter. You may look for further OpenGL stuff there or have a look at this WikiBook OpenGL Introduction (C++). I’m not aware of OpenGL tutorials for Free Pascal or Delphi treating modern OpenGL (let me know if you know).

OpenGL Pascal units (headers)

Similar to SDL 2.0, you need specific units which translate and connect your code to the OpenGL library. There is a native OpenGL unit GL which covers the main functionality of OpenGL. Additionally for modern OpenGL you need the unit GLext which covers the functionality up to OpenGL version 4.0. These units are shipped right along with the Free Pascal compiler.

In case you are interested in support of OpenGL version 4.4, you should look into the dglOpenGL.pas. This unit is not shipped natively along with the Free Pascal compiler.

Let the fun begin

Let’s have a look at the code:

Wow that is a lot of code. What you will get is this:

Result for chapter 10

The background will change slowly from green to blue. And you will get this:

Command result for chapter 10

The vendor, OpenGL version and shader version information will be different according to your system. Also, if your system doen’t support the needed OpenGL version you’ll not have “success” but rather “failure” after the compiling and linking processes. Additional information may be shown then.

The program is called “chap10_SDL2” for obvious reason.

Additionally to the SDL2 unit we load the native FPC units Classes (for TStringList support), SysUtils (for PChar functions) and GL and GLext for OpenGL support.

Thre are three constants declared. The first two are defined as the filenames of the so-called shader source files.  Basically they are simple text files which contain a script. More about shaders and the script later. The third is an array of nine GLfloat values. GLfloat is the OpenGL float variable type which in fact is translated as Pascal’s Single type. In short, these nine values describe three points in 3d space which, if connected, form a triangle. More about this later.

The first variable “sdlWindow1” is well known from previous chapters. Any variable to follow is new though. Most of them are related to OpenGL.

“sdlGLContext1” is of type TSDL_GLContext needed to create a so-called OpenGL context. In fact, this variable type is provided by SDL and a key type to set up an OpenGL conext in a simple and cross-platform manner.

The variable “i” is a simple Word variable for counting purposes.

OpenGL’s Integers and Strings

Most of the following variables are either of type GLuint or of type PGLchar. The last variable is an dynamic array of GLchars. Their specific meaning will be discussed later but GLuint is the OpenGL unsigned integer type (no negative values) which translates to Pascal’s Cardinal/Longword type. Text handling in OpenGL works by null-terminated strings of type PGLchar which translate to Pascal’s PChar. GLchar translates to Char then, obviously.

At this point you may wonder why as for SDL the null-terminated strings are used instead of simple strings (see Chapter 7 for the PAnsiChar variable type discussion). The answer again is that OpenGL is based upon C which handles strings this way. PChar equals PAnsiChar by the way.

The remaining variables “ShaderCode” of type TStringList will be used to handle the shader text files. “compilationResult” and “InfoLogLength” are of GLint type. In contrast to GLuint they allow for negative values.

First SDL2 is initilized as known. “sdlWindow1” is created as known by SDL_CreateWindow. Be careful though, in order to work with OpenGL the flag SDL_WINDOW_OPENGL has to be set!

SDL 2.0 and the OpenGL context

An OpenGL context is kind of an abstract name. It doesn’t represents just a window, even though it is created from a SDL2 window, but rather it contains everything (including the window information) that is related to this OpenGL context. The OpenGL context is therefore kind of “broader” than just a window, that is why it is called context rather than just a OpenGL window.

The function to create an OpenGL context from a SDL2 window is:

function SDL_GL_CreateContext(window: PSDL_Window): TSDL_GLContext

So, it is simple as that, just use the SDL2 window as argument and voila, you’ll get a OpenGL context, platform-independent. That is why everybody loves SDL2 to work with OpenGL. Note that the returned Context isn’t a pointer but an actual instance. So to error check against nil you need to refer to the instance’s addresse by the @ operator.

OpenGL version check and initialization

The nested if-then-statements check if at least version 3.0 of OpenGL is installed. If so, the highest available version is loaded. If not, the program is stopped and returns a text message.

If your hardware doen’t support OpenGL 3.0 or higher you should try to update your graphics driver. There is a good chance that you are able to use OpenGL 3.0 or higher then. Anyway, if the upgrade doesn’t work out or you wouldn’t want to update, you may have a look into the JEDI-SDL Chapter about OpenGL, there the old OpenGL is treated (although that chapter treats SDL 1.2, it shouldn’t be too hard to make it work with SDL 2.0 with minor changes).

Next there are three text messages printed out. These present the Vendor, the OpenGL version and the Shading language version. To get them in a readable form you need to transform the constants into strings by function glGetString. Let’s have a look at the command window again:

Command result for chapter 10

Have a look at the first three lines and you see what it could look like.

Vertex Array Object and Vertex Buffer Object

If you are new to OpenGL,  OpenGL as kind of machine with many switches. Each switch

Briefly, a Vertex Array Object (VAO) is a specific OpenGL object which contains important settings (e.g. format of vertex data) and references to other objects, including Vertex Buffer Objects (VBO). Notice, it doesn’t store the object’s data (content) itself, it just stores the reference to these objects.

The Vertex Buffer Object (VBO) contains the actual data (content). In the example case these are three vertices, each described by three float point values in cartesian space.

OpenGL Object name or ID

Because it is important to understand, in contrast to SDL where objects usually are directly submitted to a function by its pointer reference, in OpenGL you have a so-called OpenGL Object name, which actually is an integer value of GLuint type. Therefore ID is a suitable name, too. Let’s see how this works:

The VAO is created by function glGenVertexArrays( number of VAO names, pointer to VAO names array ). The first parameter determines how many VAO names I’d like to create. We just need 1. The second parameter asks for a pointer to an array of VAO names. Since VAO names are just simple GLuints, it is a simple array of GLuints. Anyway, since we just need one, a pointer to a simple GLuint variable will be suitable, too. In our case that is “VertexArrayID”. To bind (“activate”) the corresponding VAO to the OpenGL context, the function glBindVertexArray( name of VAO ) is used. The argument is the name of the VAO we just created in “VertexArrayID”.

Similar to the VAO, the VBO is created by function glGenBuffers( number of VBO names, pointer to VBO names array ). Again, we just need 1 VBO whose name should be returned to “triangleVBO”. This variable just stores an ID (object name) of GLuint type.

From the naming of “triangleVBO” it is clear to us what we intent here (representing a triangle by three vertices), anyway, how should OpenGL know? – We explain the meaning of this buffer object to OpenGL by using glBindBuffer ( target, VBO name ). There are numerous options as target but GL_VERTEX_BUFFER is the right choice here.

The actual VBO is created by glBufferData( target, size of object’s data store in bytes, pointer to data to be copied into VBO, expected usage ). This functions takes four arguments. The target is GL_VERTEX_BUFFER again. The size of the VBO’s data store in bytes is determined by Pascal’s SizeOf function applied to “triangleData”. The “triangleData” constant also holds the data to be copied into the VBO, so its pointer is suitable as the third argument. Since we are not going to change the data a lot, we should use GL_STATIC_DRAW as fourth argument.

If you are a newcomer to OpenGL, don’t worry if you are confused the first time. Most people are. And now it may even get worse :-(.

Shaders and OpenGL Shading Language

When starting with modern OpenGL the so-called Shaders are talked about a lot. Shaders are scripts written in a C-like script language called OpenGL Shading Language (GLSL). These scripts are compiled at runtime and influence the way how the graphics data is processed at certain steps in the so-called rendering pipeline of OpenGL. In fact, you can create rather complex and special effects with shaders without even changing one line of code of your source code.

Vertex Shader and Fragment Shader

There are two Shaders that are crucial and have to be set up to work with modern OpenGL. They are called  Vertex Shader and Fragment Shader. There are more Shaders not covered here, though. Each type of Shader influences different aspects of the rendering.

The Vertex Shader is the first Shader program executed in the rendering pipeline. Every vertex is “put through” the Vertex Shader program and processed accordingly, hence the name. Often this Shader is used to perform transformation operations. The Shader script used in this tutorial is shown next:

This GLSL source code is saved into a file VertexShader.txt and located in the same directory as the source code of this chapter’s example source code. I’m not going to explain this GLSL code in detail here, but a detailed explanation is found over at opengl-tutorial.org Chapter 2 where I got this Shader code from, by the way.

The Frgament Shader is the last Shader program executed in the renderin pipeline. The so-called rasterization process produces fragments. Every fragment is “put through” the Fragment Shader program and processed accordingly. The Shader script used for the Fragment Shader is:

This code is in file FragmentShader.txt and located in the same directory as the VertexShader.txt. The detailed explanation is found over at opengl-tutorial.org Chapter 2 again. Anyway, you’ll notice that there is a “color” variable (three component vector). As you see, it sets the (red,green,blue) values for the fragments to (1,0,0) which means red should be the result, red = 100%, green and blue = 0%. You may play around with these values.

Both Shaders are created by function glCreateShader( Shader type ). It returns the reference (or name) as GLuint as seen before for the VAO and VBO. We store them in the VertexShaderID and FragmenShaderID, respecitvely.

The next part is about loading the source code from the two Shader files (VertexShader.txt, FragmentShader.txt) and converting them to be used with OpenGL. First a “ShaderCode” variable of TStringList type is created. Its LoadFromFile method let us load the file contents into the variable conveniently. First for the Vertex Shader, whose file name is stored in constant “VertexShaderFile”. The variable “VertexShaderCode” is of type PGLchar, which is the way OpenGL handles strings. Since PGLchar is of type PChar anyway, the method GetText is perfectly suitable here to convert the source code string into a null-terminated array of chars. Finally, there is a simple check if the PGLchars are empty (nil), which shouldn’t be the case if the source code is pointed to as expected.

Exactly the same is done for the FragmentShader and the source code associated with “FragmentShaderCode”.

Finally, the dummy variable “ShaderCode” is free’d.

To associate the source code we stored in “VertexSourceCode” to “VertexShaderID” of GLuint type, the function glShaderSource( Shader reference, number of array elements, pointer to array of source code PGLchars, pointer to array of lengths ). The Vertex Shader reference is stored in “VertexShaderID” which is the first argument. We just have one source code, so the second argument is 1. The source code is stored VertexShaderCode, and its pointer is addressed by @VertexShaderCode as the third argument. As seen before, since we just have one element here, it is not necessary to have really an array. The fourth parameter allows for some length specification, but if set to nil it expects null-terminated arrays of chars.

The compilation is straight forward done by glCompileShader( Shader reference ). It is really advised to to error checking here, that is why it is shown how to do that. The function glGetShaderiv( Shader reference, object parameter, pointer of correct type for return value ) is used to request information about objects. First we like to know if the compilation was successful. The Shader reference is stored in “VertexShaderID”, the object parameter is GL_COMPILE_STATUS. This will return a GLint value, which can be interpreted as GL_FALSE or GL_TRUE. The result is stored in “compilationResult” by using its pointer (@compilationResult) as argument.

Right after that we request the length of the information log by GL_INFO_LOG_LENGTH. It will be greater than 0 if some information were logged (probably an error occured on compilation then). The result is returned to “InfoLogLength” by its pointer @InfoLogLength.

If an error occurs, “compilationResult” is GL_FALSE. In this case “failure” along with more specific information is printed out. I’m not going into detail here, since this shouldn’t happen. Otherwise (and that should be the case), “success” is printed out.

The very same way the Fragment Shader is compiled and checked.

The shaders have to be attached and linked by a Shader program. A Shader program is created by glCreateProgram(). The parenthesis are important here. It returns an reference of GLuint type which is stored in ProgramID.

The Shaders are attached to this Shader program by glAttacheShader( Program reference, Shader reference ). The program is linked by glLinkProgram( Program reference ). The reference for the Shader program is “ProgramID”. The references for the Shaders are “VertexShaderID” and “FragmentShaderID”, respectively.

By complete analogy to the error checking for the Shader compilation, the Shader program linking is checked. Anyway, instead of GL_COMPILE_STATUS, GL_LINK_STATUS is used.

The for-loop counts from 0 to 400. Within each cycle it first changes the background color by glClearColor( red, green, blue, alpha ). Red and alpha are constant, green and blue are varied each cycle dependend upon variable i. This makes the background slowly changing from green to blue, feel free to play around with the rgba values. To actually clear the color buffer glClear( buffer ) with GL_COLOR_BUFFER_BIT as argument is used.

glUseProgram( Shader program reference ) is used to apply the Shader program to the rendering state. “ProgramID” is the Shader program reference in the example code.

glEnableVertexAttribArray( array index ) is used in order to make the attribute array available for rendering by glDrawArrays. The index is 0 here. The “triangleVBO” is bound by glBindBuffer( target, buffer ) to the GL_BUFFER_ARRAY target to change attribute data of said VBO. Latter is done by glVertexAttribPointer( index, size, type, normalized, stride, offset of first component ) with the given arguments. Hence, the index is 0, 3 components per generic vertex attribute, each of float point type (thus, GL_FLOAT), not normalized (thus GL_FALSE), no strides between vertex attributes, no offset for the first component.

The rendering is done by glDrawArrays( type of primitive, starting index, number of elements ). The type of primitive is a triangle, hence GL_TRIANGLES is the first argument. We start at the very beginning, so index is 0. We have 3 sequential elements (vertices).

glDisableVertexAttribArray( array index ) is the counter function to glEnableVertexAttribArray( array index ), obviously. It disables the vertex attribute array.

SDL_Delay delays the loop by 20 milliseconds.

The procedure

procedure SDL_GL_SwapWindow(window: PSDL_Window)

is used to actually display the rendering result to the the window “sdlWindow1”. Keep in mind that this window has to be initialized as an OpenGL window. This procedure is comparable to SDL’s SDL_RenderPresent.

After i matching 400, the for-loop is left.

For the clean up, the shaders have to be detached from the shader program by glDetachShader( program, shader ). After that they can be deleted by glDeleteShader( shader ), and the program by glDeleteProgram( program ).

The shader script PChars are disposed by StrDispose( PChar ).

The VBO and the vertex array have to be free’d by glDeleteBuffers( number of buffer objects, pointer to array of buffers ) and glDeleteVertexArrays( number of VAOs, pointer to array of VAOs ) respectively. The first parameter is the number of objects to be deleted, which is 1 in both our cases.

To resolve the OpenGL context

procedure SDL_GL_DeleteContext(context: TSDL_GLContext)

is used.

The SDL Window is destroyed as known. Finally SDL is shut down as known by SDL_Quit.

← Chapter 9 | Chapter 11 (not existent yet) →










No One's Space

Commercial Free Pascal/SDL Project

The No One’s Space SDL game has been added to the SDL Project page. It is the first commercial title added and Klaus Vor der Landwehr (from Turtle-Games) has kindly provided an interview for us. Feel free to support the game in the greenlight state over at Steam. This game demonstrates that Free Pascal and SDL make games of commercial quality possible.

The installation instruction got extend by an explanation how to install and configure Lazarus.

No One’s Space

Short description

A commercial high quality space shooter by game developer Turtle-Games.

Showcase and Basic Data

Developer granted permission to use these screenshots.

  • Project name: No One’s Space
  • Author: Turtle Games
  • Latest version: Pre-alpha Version
  • First release date: Steam Early Access Release in 2016 (TBA)
  • Compiler: Free Pascal (via Lazarus)
  • SDL Version: 2.0
  • Further libraries: OpenGL, OpenAL, Ogg Vorbis
  • License: Commercial
  • Open source: no
  • Official website: http://www.NoOnesSpace.com

Interview with Klaus Vor der Landwehr from Turtle-Games

Could you please give a short description of No One’s Space for those who have never heard of it?

Klaus Vor der Landwehr: No One’s Space (NOS) is a single-player Retro 2D-Science-Fiction-Shooter with modern physics. It was created as a cross-breed of the classic games Wing Commander I and Star Control II. In NOS, the player experiences a cosmic conflict between four powerful races, taking the role of different heroes. In 54 challenging missions, reaching from manageable duels to large combats, the player controls a variety of vessels and has to go all out to improve his skills to master them all.

Why did you decide to choose Pascal as a programming language and SDL/SDL2 as a library for this project?

Klaus Vor der Landwehr: It wasn’t really a choice. I’m used to Pascal since my school days. I’m a self-taught. I like it.

What do you think is the most interesting Pascal/SDL/SDL2 project out there (besides your own, of course :-D)?

Klaus Vor der Landwehr: Hm, as far as it concerns the programming language, games are rarely tagged. But I’ve seen some impressive stuff right here: Projekt “W” – Phase 2 http://www.saschawillems.de/?page_id=829 (Although I can only assume that it uses SDL).

Are there any further steps for No One’s Space and/or are any new projects planned? What will they be?

Klaus Vor der Landwehr: If the game gets Greenlit, we want to release it on Steam this year (early access) and work further on it.



Pascal SDL Projects?

A new page has been set up which gives an overview of projects done in SDL with Pascal (any dialect). The projects may be games, interpreters, libraries, anything. Of course SDL should play a key role and shouldn’t be just used to set up an OpenGL window (or similar). If possible I try to have an interview with the creator of the project.

The first project listed is the famous EGSL project and its successor Pulsar2D. Both have been created by Cybermonkey who kindly gave an interview and provided a lot of screenshots to me.

Feel free to contact me to let me know about other Pascal SDL projects.

Edit: As of 09/02/2016 I added suve’s Alexland and Colorful to the project page. Thanks for the interview and the screenshots.

EGSL and Pulsar2D

Short description

EGSL and Pulsar2D are LUA script interpreters to develop games in an easy, quick and convenient way.

EGSL: Showcase and Basic Data

Developer granted permission to use these screenshots.

  • Project name: Easy Game Scripting with LUA
  • Author: Cybermonkey
  • Latest version: 1.6.0
  • Release date: 30/12/2012
  • Compiler: >= FPC 2.6.0
  • SDL Version: SDL 1.2
  • Further libraries: Vampyre Imaging Library / Lua 5.1 / Lua 5.2
  • License: zlib
  • Open source: yes
  • Official website: http://www.egsl.retrogamecoding.org

Pulsar2D: Showcase and Basic Data

Developer granted permission to use these screenshots.

  • Project name: Pulsar2d
  • Author: Cybermonkey
  • Latest version: 0.6.2
  • Release date: 31/12/2015
  • Compiler: FPC 3.0.0
  • SDL Version: SDL2
  • Further libraries: Lua 5.2
  • License: zlib
  • Open source: yes
  • Official website: http://pulsar2d.org

Interview with Cybermonkey

Could you please give a short description of EGSL and Pulsard2D for those who have never heard of it?

Cybermonkey: EGSL (Easy Game Scripting with Lua) is a Lua interpreter which allows one to code 2D games in a simple way. I could say in a “classical way” because EGSL is inspired by old BASIC dialects. The main difference between EGSL and Pulsar2D is that Pulsar2D uses now the newer SDL2 libraries (which gives us the possibility to use multiple windows). It’s as easy as that: write 10 lines of Lua code and start the script and you’ll have already a small sprite moving example. Of course it is possible to use the framework with FreePascal. Apart from that I recently ported the Pulsar2D framework to FreeBASIC. So one can code Pulsar2D games/demos whatsoever in Lua, FreePascal or FreeBASIC.

Why did you decide to choose Pascal as a programming language and SDL/SDL2 as a library for these projects?

Cybermonkey: I started programming back in the 1980s with the Commodore 64 and BASIC. I learned Turbo Pascal in school and started programming with FreePascal a few years ago. It’s the language I have the most experience with. Not to mention that the FreePascal compiler is well maintained. I chose SDL/SDL2 because of its cross platform capabilities.

What do you think is the most interesting Pascal/SDL/SDL2 project out there (besides of your own, of course :-D)?

Cybermonkey: Actually I don’t know of any other … But of course the most impressive Pascal project is Lazarus for me.

Are there any further steps for EGSL and/or Pulsar2D or any new projects planned? What will they be?

Cybermonkey: EGSL will not be developed any further. Pulsar2D wil be improved from time to time. My plans are to implement Box2D physics and easy handling of tiled based maps made with the Tiled editor. But this has no priority so it can take a long time…

At the moment I am developing a little BASIC interpreter called “AllegroBASIC”. It’s a C project, though. (The editor, however, is made with Lazarus…) Since I am using Allegro4 libs which are obsolete now, I am porting at the same time the project to SDL2 which will be named “RETROBASIC”. If there are people interested in AllegroBASIC, have a look at allegrobasic.pulsar2d.org.


Chapter 9 – Music and Sound

ATTENTION: You need the most recent Pascal translations by Tim Blume  for this chapter to work properly. Version 1.72 of Tim Blume’s Pascal translations will not work! Check step 2) in Chapter 2 for details.

This chapter will introduce you on how to load music and sounds since these are key features of every game and many applications.

SDL_mixer 2.0 for easy music and sound support

Although SDL 2.0 supports music and sound handling natively, there is an easier way to play music and sound files. The official unit SDL_mixer 2.0 (unit’s name SDL2_mixer) has been created exactly for this purpose and is maintained by the same authors (Sam Lantinga, Stephane Peter, Ryan Gordon) as SDL 2.0 itself. The Pascal translation is fortunately available, too in Tim Blume’s header translations.

Supported music and sound file formats in SDL 2.0

According to the official SDL2_mixer documentation the following music and sound formats are supported:

  • WAVE/RIFF (.wav)
  • AIFF (.aiff)
  • VOC (.voc)
  • MOD (.mod .xm .s3m .669 .it .med and more) requiring libmikmod on system
  • MIDI (.mid) using timidity or native midi hardware
  • OggVorbis (.ogg) requiring ogg/vorbis libraries on system
  • MP3 (.mp3) requiring SMPEG or MAD library on system
  • FLAC (.flac) requiring the FLAC library on system

You’ll need these files:

File name
SDL2_mixer dynamic link library
SDL2_mixer-2.0.1-win32-x86.zip (32-bit Windows)
SDL2_mixer-2.0.1-win32-x64.zip (64-bit Windows)
This is the corresponding dynamic link library file for the unit for Windows. Note: Mac OS X and Linux versions are also available.
dial.wav sound file dial.wav
A simple telephone dial sound. Source: pdsounds. License: Public domain.
In my mind.ogg music file In my mind.ogg
In my mind.ogg
A nice music sample. Source/Creator: First. License: CC BY-ND 3.0.

You should extract the zip-file and get several files. These are four license text files and a readme text file, furthermore you have eight dll files including the important SDL2_mixer.dll. The other dll files are necessary to play the different sound and music formats. Copy all the files to the Windows system32-folder (or the corresponding place). If you forget this and run the examples below you will get an error with exitcode = 309.

Now that you are prepared, let’s have an overview of the code.

When running this program, you’ll get two windows. A simple SDL 2.0 window without any content (white) and the title “Music and Sound window” and a console window showing a simple menu (list) of possible actions to play around with the music and sound. Keep in mind that the focus has to be on the SDL 2.0 window for the key recognition to work.

Chapter 9 application preview

Let’s start with the first part of the code.

The program is called “chap9_SDL2”. It uses the SDL2 and the new SDL2_mixer unit.

We’re going to use event handling as discussed in Chapter 8 to check what keys have been pressed. Consequently we need a variable “sdlWindow1” for the SDL 2.0 application window (for the focus) and an event variable “sdlEvent”.

The pointer variable “music” is of the new type PMix_Music and points at the loaded music file data later. The “sound” pointer variable is of type PMix_Chunk and points at the loaded sound file data later. Note: Each song is referenced by an own PMix_Music pointer and each sound effect (e.g. explosions, shots, …) is referenced by an own PMix_Chunk pointer.

What is the difference between music and sound?

Music is associated with PMix_Music pointers and sounds are associated with PMix_Chunk pointers, but why distinguish them at all? – Well, it is convenient to have them separated since they have rather different properties. Music is usually several minutes long, sounds are usually just a few seconds short. It is usually just one song played at a time, sounds need to mix up if necessary. For music it usually doesn’t plays a role if it is sligthly delayed to when it should start, for sounds a larger delay usually means a strange feeling for the player. So, for music there is exactly one channel reserved where the music is played. For sounds eight sound channels are available to make it possible for them to mix up. Now let’s get back to the code.

The variable “exitloop” is a boolean variable to determine when the main loop of the program should be exited.

The program is initialized by SDL_Init as known. Note though that not only SDL_INIT_VIDEO but additionally SDL_INIT_AUDIO is set. They are combined by the or operator (not the and operator :-)!).  The window is set up afterwards by SDL_CreateWindow as known.

To initialize SDL2_mixer the function

function Mix_OpenAudio(frequency: Integer; format: UInt16; channels: Integer; chunksize: Integer): Integer

has to be called. It requests four parameters. These are the frequency, the audio format, the channels (mono or audio) and the chunksize. All these parameters are of Integer type. Function Mix_OpenAudio returns 0 on success and -1 on errors.

The frequency in Hertz (1/s) usually is 22050 Hz or MIX_DEFAULT_FREQUENCY in games but double as high for CD quality sound (44100 Hz). The higher the frequency, the more CPU power is needed.

Next we have to define the audio format. It determines how the audio data is stored. MIX_DEFAULT_FORMAT equals AUDIO_S16SYS. Different values are given in the following list (from official SDL2_mixer documentation):

  • Format constant name Description
  • AUDIO_U8 Unsigned 8-bit samples
  • AUDIO_S8 Signed 8-bit samples
  • AUDIO_U16LSB Unsigned 16-bit samples, in little-endian byte order
  • AUDIO_S16LSB Signed 16-bit samples, in little-endian byte order
  • AUDIO_U16MSB Unsigned 16-bit samples, in big-endian byte order
  • AUDIO_S16MSB Signed 16-bit samples, in big-endian byte order
  • AUDIO_U16 same as AUDIO_U16LSB (for backwards compatability probably)
  • AUDIO_S16 same as AUDIO_S16LSB (for backwards compatability probably)
  • AUDIO_U16SYS Unsigned 16-bit samples, in system byte order
  • AUDIO_S16SYS Signed 16-bit samples, in system byte order

Then we decide for a sound channel type, which means either stereo or mono. For stereo sound we choose 2 and for mono we choose 1 as value. MIX_DEFAULT_CHANNELS equals stereo output.

Finally the chunksize has to be set, where 4096 bytes per sample is a good and default value. Too low values may lead to skipping samples. Too high values may lead to delayed playing.

Loading music and sounds from files in SDL 2.0

We will load the music by

function Mix_LoadMUS(_file: PAnsiChar): PMix_Music.

_file can be the absolute path. If the Pascal file and the music file are in the same folder the file name is sufficient (as shown in the example). If the loading was unsuccessful, the function returns nil. The volume can be set by

function Mix_VolumeMusic(volume: Integer): Integer.

The volume can be set between 0 (silence) to 128 (maximum volume). The latter equals MIX_MAX_VOLUME. By the way, if you set -1 as argument, the return value corresponds to the set volume.

Quite similar sound files are loaded by

function Mix_LoadWAV(_file: PAnsiChar): PMix_Chunk.

Although the function’s name doesn’t indicate this, use this function to load the sound files of any format (Wave, Aiff, Riff, Ogg, Voc), not only for .wav sound files. It return nil on error. There is alittle difference when setting the volume by

function Mix_VolumeChunk(chunk: PMix_Chunk; volume: Integer): Integer.

Instead of just setting a general volume, the volume is bound to a certain sound. In the example case the sound is in variable “sound”. Just to mention it here, there is a third possibility, to set the volume for a certain channel:

function Mix_Volume(channel: Integer; volume: Integer): Integer.

This can be quite handy, anyway, channels are discussed a little bit later below. If your argument is -1 the average volume will be returned.

Here nothing new can be found. The menu is printed out and some memory is allocated to the event pointer. Let’s proceed.

Playing, pausing, resuming music and sounds

The main application loop is entered and should be left if variable “exitloop” is true.

As known from previous Chapter 8 about event handling, we firstly poll for events by SDL_PollEvent() and enter a further loop. Secondly, if there are events found waiting to be processed, we check by a case statement what exact key has been pressed.

For each key a different music or sound related function is used to do something. Let’s discuss them now in detail. We start with the functions used for keys 1-4:

function Mix_PlayMusic(music: PMix_Music; loops: Integer): Integer

procedure Mix_PauseMusic

procedure Mix_ResumeMusic

procedure Mix_RewindMusic

Mix_PlayMusic plays music. The first argument is the music itself which we previously got from the example .ogg music file and associated with the “music” pointer of PMix_Music type. The second argument determines how often the music is played. Additionally -1 means infinite repetition. This function returns 0 on success and -1 on error.

The meaning of the three procedures Mix_PauseMusic, Mix_ResumeMusic and Mix_RewindMusic ist obvious from their names. They are used to pause, resume (if paused before) and rewind the played music.

The analogous function and procedures for sound channels are shown now:

function Mix_PlayChannel(channel: Integer; chunk: PMix_Chunk; loops: Integer): Integer

procedure Mix_Pause(channel: Integer)

procedure Mix_Resume(channel: Integer)

As you can see the function Mix_PlayChannel has three parameters. The first parameter asks for a channel with which the sound should be associated. SDL2_mixer provides eight sound channels. Usually you should use -1 which means the first free channel will be used to play the sound. Anyway, you could specifiy a certain channel here if you like. The second parameter asks for a sound pointer of PMix_Chunk type. The  third parameter is the same as for music, -1 means an infinite loop. Attention though for specific repetitions. The value for loops is increased by 1. So, if you want a sound to be played once, you need the argument to be 0. The return value corresponds to the sound channel the sound is played on, it is -1 on error.

The procedures Mix_Pause and Mix_Resume are self-explanatory. Use them to pause or resume a certain channel, which is the argument. If the argument is -1 (as in the example code) you pause or resume all channels. By the way, you may have noticed that there is not a rewind analogue, because sounds are not expected to be rewound.

Fading and distance effects

Important to know about effects like fading. They are performed on the fly to your data, so the more effects you use, the more computational power they require. It is important to unregister effects you don’t need anymore.

These are the four fade functions triggered by the next keys (A-F):

function Mix_FadeInMusic(music: PMix_Music; loops: Integer; ms: Integer): Integer

function Mix_FadeOutMusic(ms: Integer): Integer

function Mix_FadeInChannel(channel: Integer; chunk: PMix_Chunk; loops: Integer; ms: Integer): Integer

function Mix_FadeOutChannel(which: Integer; ms: Integer): Integer

The function Mix_FadeInMusic works the very same way as Mix_PlayMusic above, but there is a further parameter which allows for a fade in effect in milliseconds. 3000 milliseconds equals 3 seconds. It returns 0 on success and -1 on error.

Mix_FadeOutMusic fades out the playing music within the given time in milliseconds in the moment the function is called (hence the key is pressed in the example program). Attention, it returns 1 on success and 0 on error.

Quite similar the functions Mix_FadeInChannel and Mix_FadeOutChannel work. Instead of the music pointer, the sound pointer has to be given. Additionally the channel has to be given. By the way, also here the number of times the sound is played is increased by 1, so if you want to play a sound with fade in effect once, the argument has to be 0. Both functions return 0 on success and -1 on error.

The functions triggered by the keys G-M are:

function Mix_SetPanning(channel: Integer; left: UInt8; right: UInt8): Integer

For setting the panning you need the channel to which panning should be applied and the volume values which may vary from 0 (quiet) to 255 (loudest). For a consistent panning effect you may substract the left value from the right value (left: volume, right: 255-volume). To unregister this effect, you should set both values to 255, which is recommended to be done if you don’t need panning anymore. The function returns 0 on errors.

function Mix_SetDistance(channel: Integer; distance: UInt8): Integer

The higher the distance the quieter the sound appears. The value can range between 0 (near) and 255 (far). If distance is set to 0 the effect is unregistered. It returns 0 on errors.

function Mix_SetPosition(channel: Integer; angle: SInt16; distance: UInt8): Integer

This function adjusts volumes according to an angle and a distance value, hence it combines the effects of the two functions discussed before for panning and distance. The distance value works the same way as discussed for Mix_SetDistance. Angle of 0 (degree) means in front of you, 90 means directly to the right, 180 means directly behind, 270 means directly to the left.

Finally, if the SDLK_ESCAPE has been pressed, the loop stopping variable “exitloop” is set to true, which will stop the main loop.

Within the main loop a short delay of 5 milliseconds is used to prevent the application from running an empty loop no events are waiting.

The clean up means freeing sdlEvent, and use the procedures Mix_FreeMusic and Mix_FreeChunk to free the music and sound data.

procedure Mix_FreeMusic(music: PMix_Music)

procedure Mix_FreeChunk(chunk: PMix_Chunk)

The arguments have to be the music and sound pointer respectively.

SDL_mixer 2.0 has to be closed by

procedure Mix_CloseAudio.

Finally SDL 2.0 and the application are shut down as known.

← previous Chapter | Chapter 10 →

Chapter 1 – Introduction

The introduction is short.

What is SDL or rather SDL2?

SDL abbreviates Simple Direct Media Layer. In August 2013 the official successor of original SDL (SDL 1.2) has been released, simply called SDL 2.0 (or SDL2). It is a library to develop powerful applications for many different operating systems (platforms) by learning only one set of commands. This is called cross-platform development. The following platforms are officially supported by SDL2:

  • Windows
  • Mac OS X
  • Linux
  • iOS
  • Android.

Internally the SDL library layer translates your commands to the platform specific commands, which is reflected by the followig diagram.

SDL2 Layers Diagram
Image by Adriatikus at English Wikipedia [Public domain], Wikimedia
SDL2 Layer Diagram
It’s especially meaningful to use the SDL library if you plan to develop games or need fast paced rendering. Jump and run-, Role-playing-, Real time/turn based strategy-, side-scrolling-, arcade-, board-, card-, simulation-, multi-user dungeon-, puzzle-, shooter-, network games and so on are possible, and any combination of these ;-).


The SDL 2.0 library, as well as the units for translation, are licensed under the zlib license. This license grants a high degree of freedom. So even closed-source, commercial applications and games are possible with SDL 2.0 and Free Pascal. As a sidenote, you are free to choose the MPL license for the units, if you like.

How to get SDL2 for Free Pascal or Object Pascal?

There are several SDL 2.0 units out there (see comparison and discussion here) which translate SDL 2.0 to Pascal, since originally it has been written in C. Over time it turned out that Tim Blume’s SDL 2.0 units are the best choice to use if you like to get into SDL 2.0 development in Free Pascal or Object Pascal.

A detailed installation instruction to set your system up for SDL 2.0 development under Pascal is found in Chapter 2 for Windows or Linux. If you did install SDL 2.0 for Free Pascal or Object Pascal already, proceed to Chapter 3.

Chapter 2 (Windows) → | Chapter 2 (Linux) → | Chapter 3 →