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Prefer downscaling in SDL_GetSurfaceImage. 

This implements the ideas described in  #10536
This commit is contained in:
Kaktus514 2024-08-15 13:41:20 +02:00 committed by Sam Lantinga
parent 4ac5d4506b
commit 3586df3151
3 changed files with 31 additions and 7 deletions
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5
include/SDL3/SDL_mouse.h
View File

@ -423,8 +423,9 @@ extern SDL_DECLSPEC SDL_Cursor * SDLCALL SDL_CreateCursor(const Uint8 * data,
* situations. For example, if the original surface is 32x32, then on a 2x
* macOS display or 200% display scale on Windows, a 64x64 version of the
* image will be used, if available. If a matching version of the image isn't
* available, the closest size image will be scaled to the appropriate size
* and be used instead.
* available, the closest larger size image will be downscaled to the
* appropriate size and be used instead, if available. Otherwise, the closest
* smaller image will be upscaled and be used instead.
*
* \param surface an SDL_Surface structure representing the cursor image.
* \param hot_x the x position of the cursor hot spot.

5
include/SDL3/SDL_video.h
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@ -1341,8 +1341,9 @@ extern SDL_DECLSPEC const char * SDLCALL SDL_GetWindowTitle(SDL_Window *window);
* situations. For example, if the original surface is 32x32, then on a 2x
* macOS display or 200% display scale on Windows, a 64x64 version of the
* image will be used, if available. If a matching version of the image isn't
* available, the closest size image will be scaled to the appropriate size
* and be used instead.
* available, the closest larger size image will be downscaled to the
* appropriate size and be used instead, if available. Otherwise, the closest
* smaller image will be upscaled and be used instead.
*
* \param window the window to change.
* \param icon an SDL_Surface structure containing the icon for the window.

28
src/video/SDL_surface.c
View File

@ -514,18 +514,25 @@ SDL_Surface *SDL_GetSurfaceImage(SDL_Surface *surface, float display_scale)
return surface;
}
// Find closest image. Images that are larger than the
// desired size are preferred over images that are smaller.
SDL_Surface *closest = NULL;
int desired_w = (int)SDL_round(surface->w * display_scale);
int desired_h = (int)SDL_round(surface->h * display_scale);
int desired_size = desired_w * desired_h;
int closest_distance = -1;
int closest_size = -1;
for (int i = 0; images[i]; ++i) {
SDL_Surface *candidate = images[i];
int size = candidate->w * candidate->h;
int delta_w = (candidate->w - desired_w);
int delta_h = (candidate->h - desired_h);
int distance = (delta_w * delta_w) + (delta_h * delta_h);
if (closest_distance < 0 || distance < closest_distance) {
if (closest_distance < 0 || distance < closest_distance ||
(size > desired_size && closest_size < desired_size)) {
closest = candidate;
closest_distance = distance;
closest_size = size;
}
}
SDL_free(images);
@ -536,8 +543,23 @@ SDL_Surface *SDL_GetSurfaceImage(SDL_Surface *surface, float display_scale)
return closest;
}
// We need to scale an image to the correct size
return SDL_ScaleSurface(closest, desired_w, desired_h, SDL_SCALEMODE_LINEAR);
// We need to scale the image to the correct size. To maintain good image quality, downscaling
// is done in steps, never reducing the width and height by more than half each time.
SDL_Surface *scaled = closest;
do {
int next_scaled_w = SDL_max(desired_w, (scaled->w + 1) / 2);
int next_scaled_h = SDL_max(desired_h, (scaled->h + 1) / 2);
SDL_Surface *next_scaled = SDL_ScaleSurface(scaled, next_scaled_w, next_scaled_h, SDL_SCALEMODE_LINEAR);
if (scaled != closest) {
SDL_DestroySurface(scaled);
}
scaled = next_scaled;
if (!scaled) {
return NULL;
}
} while (scaled->w != desired_w || scaled->h != desired_h);
return scaled;
}
void SDL_RemoveSurfaceAlternateImages(SDL_Surface *surface)