Preventing Cursor Blur When Scaling

1#include <SDL.h>
2#include <SDL_image.h>
3#include <unordered_map>
4#include <string>
5
6class ScalableCursor {
7public:
8  struct CursorSize {
9    int width;
10    int height;
11    SDL_Cursor* cursor;
12  };
13
14  ScalableCursor() {
15    // Load cursor variants
16    LoadCursorVariant("cursor_16.png", 16, 16);
17    LoadCursorVariant("cursor_32.png", 32, 32);
18    LoadCursorVariant("cursor_64.png", 64, 64);
19  }
20
21  void UpdateForScale(float windowScale) {
22    // Choose best cursor size for current scale
23    int targetSize = static_cast<int>(16.0f * windowScale);
24
25    SDL_Cursor* bestCursor{nullptr};
26    int smallestDiff{INT_MAX};
27
28    for (const auto& [size, cursorInfo] : Cursors) {
29      int diff{std::abs(size - targetSize)};
30      if (diff < smallestDiff) {
31        smallestDiff = diff;
32        bestCursor = cursorInfo.cursor;
33      }
34    }
35
36    if (bestCursor) {
37      SDL_SetCursor(bestCursor);
38    }
39  }
40
41private:
42  void LoadCursorVariant(
43    const std::string& path,
44    int width,
45    int height
46  ) {
47    SDL_Surface* surface{IMG_Load(path.c_str())};
48    if (!surface) {
49      return;
50    }
51
52    SDL_Cursor* cursor{SDL_CreateColorCursor(
53      surface, width/2, height/2)};
54    SDL_FreeSurface(surface);
55
56    if (cursor) {
57      Cursors[width] = {width, height, cursor};
58    }
59  }
60
61  std::unordered_map<int, CursorSize> Cursors;
62};

1class PixelPerfectCursor {
2public:
3  void Render(
4    SDL_Renderer* renderer,
5    int mouseX,
6    int mouseY,
7    float scale
8  ) {
9    // Calculate pixel-aligned position
10    int alignedX{static_cast<int>(
11      std::round(mouseX / scale) * scale)};
12    int alignedY{static_cast<int>(
13      std::round(mouseY / scale) * scale)};
14
15    // Set nearest-neighbor scaling
16    SDL_SetHint(
17      SDL_HINT_RENDER_SCALE_QUALITY, "0");
18
19    SDL_Rect destRect{
20      alignedX,
21      alignedY,
22      static_cast<int>(CursorWidth * scale),
23      static_cast<int>(CursorHeight * scale)
24    };
25
26    SDL_RenderCopy(
27      renderer,
28      CursorTexture,
29      nullptr,
30      &destRect
31    );
32  }
33
34private:
35  SDL_Texture* CursorTexture;
36  int CursorWidth{16};
37  int CursorHeight{16};
38};