Any good game has a custom mouse cursor. You may think it would be a good idea to have a SDL2 surface or SDL2 texture and render it as any other sprite right at the mouse position to simulate a mouse cursor. DO NOT do this! The mouse cursor is handled separatly from the other rendering to have it smooth and working in critical situations.
The following code shows how to set up a custom mouse cursor with SDL2 the correct way.
program SDL_MouseCursor; uses SDL2, SDL2_image; var sdlWindow1: PSDL_Window; sdlRenderer: PSDL_Renderer; sdlSurface1: PSDL_Surface; sdlMouseCursor: PSDL_Cursor; sdlEvent: TSDL_Event; ExitLoop: Boolean = False; begin //initilization of video subsystem if SDL_Init(SDL_INIT_VIDEO) < 0 then Halt; SDL_CreateWindowAndRenderer(500, 500, SDL_WINDOW_SHOWN, @sdlWindow1, @sdlRenderer); if (sdlWindow1 = nil) or (sdlRenderer = nil) then Halt; sdlSurface1 := IMG_Load('Cursor.png' ); if sdlSurface1 = nil then Halt; // create and set new mouse cursor sdlMouseCursor := SDL_CreateColorCursor(sdlSurface1, 8, 8); if sdlMouseCursor = nil then Halt; SDL_SetCursor(sdlMouseCursor); while ExitLoop = False do begin // exit loop if mouse button pressed while SDL_PollEvent(@sdlEvent) = 1 do if sdlEvent.type_ = SDL_MOUSEBUTTONDOWN then ExitLoop := True; SDL_SetRenderDrawColor(sdlRenderer, 128, 128, 128, SDL_ALPHA_OPAQUE); SDL_RenderClear(sdlRenderer); SDL_RenderPresent(sdlRenderer); SDL_Delay( 20 ); end; SDL_FreeCursor(sdlMouseCursor); SDL_FreeSurface(sdlSurface1); SDL_DestroyRenderer(sdlRenderer); SDL_DestroyWindow (sdlWindow1); //shutting down video subsystem SDL_Quit; end.
To have a custom mouse cursor we need a variable of type PSDL_Cursor. We call it “sdlMouseCursor” here.
The result looks like this:
sdlSurface1 := IMG_Load('Cursor.png' ); if sdlSurface1 = nil then Halt; // create and set new mouse cursor sdlMouseCursor := SDL_CreateColorCursor(sdlSurface1, 8, 8); if sdlMouseCursor = nil then Halt; SDL_SetCursor(sdlMouseCursor);
This is the interesting part of the code with regard to creating a custom mouse cursor. The cursor’s image is defined by a SDL surface. We create the SDL surface as known from a previous chapter from a png image file to “sdlSurface1” here.
The custom mouse cursor is created by the following function, which returns nil on error.
SDL_CreateColorCursor(surface: PSDL_Surface; hot_x: SInt32; hot_y: SInt32): PSDL_Cursor
It needs the surface to use as cursor image and two coordinates (hot_x/hot_y) as arguments. They determine where the actual hitting point for this cursor is. Since the example cursor image is of dimensions 16×16 px and represents a cross, the “hot” (hitting) coordiates are (8/8), hence the cross’ center is used for hitting a button or something. In contrast you may imagine a typical arrow shaped mouse cursor, where the hitting point has to be adjusted to be right on the tip of the arrow in the arrow’s image.
If the cursor creation has been successful, it is necessary to set it to be the actual cursor. You may have created many different cursors, so tell SDL which one to use by the following procedure.
The remaining part of the code is just rendering a 500 by 500 pixels window with a grey (128, 128, 128) background that is updated as long as no mouse button has been pressed.
Finally do not forget to free the mouse cursor by SDL_FreeCursor(mouse cursor) as shown.