Image Scaling and Aspect Ratios

Optimizing Performance with Scaled Images

How can I optimize performance when working with many scaled images simultaneously?

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Optimizing performance when working with many scaled images simultaneously is crucial for maintaining smooth gameplay. Here are several strategies you can employ:

Use Texture Atlases

Combine multiple images into a single texture atlas. This reduces the number of texture switches during rendering:

1#include <SDL.h>
2#include <SDL_image.h>
3
4#include <vector>
5
6struct Sprite {
7  SDL_Rect srcRect;
8  SDL_FRect dstRect;
9};
10
11class TextureAtlas {
12public:
13  TextureAtlas(SDL_Renderer* renderer,
14               const char* file) {
15    texture = IMG_LoadTexture(renderer, file);
16  }
17
18  ~TextureAtlas() {
19    SDL_DestroyTexture(texture);
20  }
21
22  void RenderSprites(SDL_Renderer* renderer,
23                     const std::vector<Sprite>&
24                     sprites) {
25    for (const auto& sprite : sprites) {
26      SDL_RenderCopyF(renderer, texture,
27                      &sprite.srcRect,
28                      &sprite.dstRect);
29    }
30  }
31
32private:
33  SDL_Texture* texture;
34};
35
36// Usage
37TextureAtlas atlas(renderer, "atlas.png");
38std::vector<Sprite> sprites = {/* ... */};
39atlas.RenderSprites(renderer, sprites);

Implement Culling

Only render images that are visible on the screen:

1bool IsVisible(const SDL_FRect& rect,
2               int screenWidth,
3               int screenHeight) {
4  return rect.x<screenWidth && rect.y<
5    screenHeight && rect.x + rect.w > 0 &&
6    rect.y + rect.h > 0;
7}
8
9void RenderVisibleSprites(
10  SDL_Renderer* renderer,
11  const std::vector<Sprite>& sprites,
12  int screenWidth,
13  int screenHeight) {
14  for (const auto& sprite : sprites) {
15    if (IsVisible(sprite.dstRect, screenWidth,
16                  screenHeight)) {
17      SDL_RenderCopyF(renderer, texture,
18                      &sprite.srcRect,
19                      &sprite.dstRect);
20    }
21  }
22}

Use Hardware Scaling

Let the GPU handle scaling by using SDL_RenderCopyF() instead of pre-scaling your images:

1void RenderScaledSprite(SDL_Renderer* renderer,
2                        SDL_Texture* texture,
3                        const SDL_Rect& src,
4                        const SDL_FRect& dst,
5                        float scale) {
6  SDL_FRect scaledDst = {
7    dst.x, dst.y, dst.w * scale, dst.h * scale};
8  SDL_RenderCopyF(renderer, texture, &src,
9                  &scaledDst);
10}

Implement Level-of-Detail (LOD)

Use lower resolution textures for distant objects:

1enum class LOD { High, Medium, Low };
2
3struct MultiLODSprite {
4  SDL_Texture* highRes;
5  SDL_Texture* mediumRes;
6  SDL_Texture* lowRes;
7  SDL_FRect dstRect;
8};
9
10LOD GetLOD(float distance) {
11  if (distance < 100) return LOD::High;
12  if (distance < 300) return LOD::Medium;
13  return LOD::Low;
14}
15
16void RenderMultiLODSprite(
17  SDL_Renderer* renderer,
18  const MultiLODSprite& sprite,
19  float distance) {
20  SDL_Texture* texture;
21  switch (GetLOD(distance)) {
22  case LOD::High:
23    texture = sprite.highRes;
24    break;
25  case LOD::Medium:
26    texture = sprite.mediumRes;
27    break;
28  case LOD::Low:
29    texture = sprite.lowRes;
30    break;
31  }
32  SDL_RenderCopyF(renderer, texture, nullptr,
33                  &sprite.dstRect);
34}

Batch Similar Sprites

Group sprites with the same texture and render them together:

1void RenderBatchedSprites(
2  SDL_Renderer* renderer,
3  const std::vector<std::pair<
4    SDL_Texture*, SDL_FRect>>& sprites) {
5  SDL_Texture* currentTexture = nullptr;
6  for (const auto& [texture, dstRect] :
7       sprites) {
8    if (texture != currentTexture) {
9      currentTexture = texture;
10      SDL_SetTextureColorMod(
11        currentTexture, 255, 255, 255);
12    }
13    SDL_RenderCopyF(renderer, currentTexture,
14                    nullptr, &dstRect);
15  }
16}

By implementing these optimization techniques, you can significantly improve the performance of your SDL2 game when dealing with many scaled images. Remember to profile your game to identify bottlenecks and focus your optimization efforts where they'll have the most impact.

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