SDL: Custom Mouse Cursor Appearance

Yes, SDL provides functions to hide the default system cursor and display your own custom cursor graphics.

Key Functions

1. SDL_CreateCursor(): Creates a cursor using monochrome (2-color) bitmap data. This is an older style but universally supported. You provide pointers to the pixel data and a mask, along with the cursor's dimensions and hot-spot coordinates (the precise point of the cursor that corresponds to the mouse position).
2. SDL_CreateColorCursor(): Creates a cursor from an SDL_Surface. This is more flexible as it allows full-color cursors with alpha transparency. You provide the surface containing the cursor image and the hot-spot coordinates. The surface should typically be small (e.g., 32x32 pixels).
3. SDL_SetCursor(): Sets the currently active cursor for the application. You pass the SDL_Cursor* returned by one of the creation functions. To revert to the default system cursor, you can call SDL_SetCursor(SDL_GetDefaultCursor());.
4. SDL_ShowCursor(): Toggles the visibility of the cursor. Use SDL_ShowCursor(SDL_DISABLE) to hide it and SDL_ShowCursor(SDL_ENABLE) to show it. You usually hide the system cursor before setting your custom one if you don't want both potentially visible.
5. SDL_FreeCursor(): Frees the memory associated with an SDL_Cursor that you created. You should call this when you no longer need the custom cursor.
6. SDL_GetDefaultCursor(): Returns a pointer to the default system cursor.

Simple Example (using SDL_CreateColorCursor)

This example assumes you have an SDL_Surface* cursorSurface loaded with your desired cursor image (e.g., a crosshair loaded from a BMP or PNG file using SDL_LoadBMP or the SDL_image library).

1#include <SDL.h>
2// Assume SDL_image is linked for PNG/other formats
3// #include <SDL_image.h>
4
5// Function to load a surface (implement elsewhere)
6SDL_Surface* LoadSurface(const char* path);
7
8int main(int argc, char** argv) {
9  // ... SDL Initialization ...
10  SDL_Window* window = SDL_CreateWindow(/*...*/);
11  // ... Error handling ...
12
13  SDL_Surface* cursorSurface = LoadSurface("crosshair.png"); // Load your image
14  if (!cursorSurface) {
15    // Handle error: image not loaded
16    return 1;
17  }
18
19  // Define hotspot (e.g., center of a 32x32 image)
20  int hot_x = cursorSurface->w / 2;
21  int hot_y = cursorSurface->h / 2;
22
23  SDL_Cursor* customCursor = SDL_CreateColorCursor( 
24    cursorSurface, hot_x, hot_y                   
25  );                                              
26
27  if (!customCursor) {
28    std::cerr << "Failed to create color cursor: "
29              << SDL_GetError() << '\\n';
30    SDL_FreeSurface(cursorSurface);
31    // ... Cleanup ...
32    return 1;
33  }
34
35  SDL_SetCursor(customCursor); 
36
37  // --- Main Loop ---
38  SDL_Event e;
39  bool quit = false;
40  while (!quit) {
41    while (SDL_PollEvent(&e)) {
42      if (e.type == SDL_QUIT) quit = true;
43      // ... Handle other events ...
44    }
45    // ... Update and Render ...
46  }
47  // --- End Loop ---
48
49  SDL_FreeCursor(customCursor);  Release the cursor resource
50  SDL_FreeSurface(cursorSurface); // Release the surface memory
51  // ... Other cleanup (Destroy Window, SDL_Quit) ...
52  return 0;
53}

Important Considerations

• Surface Format: Ensure the SDL_Surface used for SDL_CreateColorCursor has an appropriate format, often one with an alpha channel for transparency (like SDL_PIXELFORMAT_RGBA32).
• Performance: Creating cursors can take some time. It's best practice to create your custom cursors once during initialization rather than repeatedly inside the main loop.
• Resource Management: Remember to free the cursor using SDL_FreeCursor and the surface using SDL_FreeSurface when they are no longer needed to avoid memory leaks.

We cover surface loading, manipulation, and more advanced cursor handling, including system cursors - SDL_CreateSystemCursor() - in greater detail later in the course.