CODEWITHSUNDEEP
csdlsdl-2
Brendan Rius
Brendan Rius

Reputation: 610

Slow pixel per pixel rendering with SDL2's textures

I am trying to create a image pixel-per-pixel and display it on the screen with SDL. The image has to be refreshed and displayed again ~50 times per second (I am looking for a 50 FPS game). I tried to create a simple program to illustrate what I want to do: I create a 1280 * 720 window and texture which I alternately fill with green and red. The problem is that the code runs very slowly (~8 FPS). Where did I mess up?

Here's my code

  SDL_Texture   *display;
  SDL_Window    *window;
  SDL_Renderer  *renderer;
  int           x;
  int           y;
  int           a = 255;
  int           b = 0;

  window = SDL_CreateWindow(gl_title, SDL_WINDOWPOS_CENTERED,
                            SDL_WINDOWPOS_CENTERED, gl_width, gl_height, 0);
  renderer = SDL_CreateRenderer(window, 0, SDL_RENDERER_ACCELERATED |
                                           SDL_RENDERER_TARGETTEXTURE |
                                           SDL_RENDERER_PRESENTVSYNC);
  display = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888,
                              SDL_TEXTUREACCESS_TARGET, gl_width, gl_height);
  while (true)
    {
      SDL_SetRenderTarget(renderer, display);
      SDL_SetRenderDrawColor(renderer, a, b, 0, 255);
      for (x = 0; x < gl_width; ++x)
        {
          for (y = 0; y < gl_height; ++y)
            {
              SDL_RenderDrawPoint(renderer, x, y);
            }
        }
      a = a == 255 ? 0 : 255;
      b = b == 255 ? 0 : 255;
      SDL_SetRenderTarget(renderer, NULL);
      SDL_RenderCopy(renderer, display, NULL, NULL);
      SDL_RenderPresent(renderer);
    }

Upvotes: 1

Views: 1562

Answers (1)

2501
2501

Reputation: 25752

Drawing on a screen using a function for every pixel is going to be slow. You can manually write the pixels in a loop and avoid the cost of calling the function every time or use one of the SDL provided functions that do that for you:

SDL_RenderFillRect

SDL_RenderDrawLines

SDL_RenderDrawPoints

SDL_RenderDrawRect

Upvotes: 2

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