Skip to content

Save non-alpha pngs as RGB not RGBA, handle arbitrary surface pitch properly (miniz backend) #560

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
wants to merge 2 commits into from
Closed

Save non-alpha pngs as RGB not RGBA, handle arbitrary surface pitch properly (miniz backend) #560

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
6a42626
Save non-alpha pngs as RGB not RGBA
ankith26 Jun 4, 2025
b70518d
Format if-else block in SDL style
ankith26 Aug 2, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
59 changes: 52 additions & 7 deletions src/IMG_png.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -766,15 +766,60 @@ static int IMG_SavePNG_RW_miniz(SDL_Surface *surface, SDL_RWops *dst)
return IMG_SetError("Passed NULL dst");
}

if (surface->format->format == png_format) {
png = tdefl_write_image_to_png_file_in_memory(surface->pixels, surface->w, surface->h, surface->format->BytesPerPixel, surface->pitch, &size);
} else {
SDL_Surface *cvt = SDL_ConvertSurfaceFormat(surface, png_format, 0);
if (cvt) {
png = tdefl_write_image_to_png_file_in_memory(cvt->pixels, cvt->w, cvt->h, cvt->format->BytesPerPixel, cvt->pitch, &size);
SDL_FreeSurface(cvt);
/* miniz only supports RGB and RGBA, it does not support palette.
* So we:
* - pick RGBA if surface has per-pixel alpha or if a palette entry has alpha.
* - pick RGB in all other cases.
* Just like the libpng implementation, global alpha and colorkey gets
* ignored here for consistency.
*/
int do_rgba = SDL_ISPIXELFORMAT_ALPHA(surface->format->format);
if (!do_rgba && SDL_ISPIXELFORMAT_INDEXED(surface->format->format)) {
SDL_Palette *pal = surface->format->palette;
if (pal) {
for (int i = 0; i < pal->ncolors; i++) {
if (pal->colors[i].a != SDL_ALPHA_OPAQUE) {
do_rgba = 1;
break;
}
}
}
}

Uint32 cvt_fmt = do_rgba ? png_format : SDL_PIXELFORMAT_RGB24;
SDL_Surface *cvt = NULL;
Uint8 *pixels = surface->pixels;
int bpp = surface->format->BytesPerPixel;
int pitch = surface->pitch;
if (surface->format->format != cvt_fmt) {
cvt = SDL_ConvertSurfaceFormat(surface, cvt_fmt, 0);
pixels = cvt ? cvt->pixels : NULL;
bpp = cvt ? cvt->format->BytesPerPixel : 0;
pitch = cvt ? cvt->pitch : 0;
}
if (pixels) {
int w = surface->w;
int h = surface->h;
int tightened_pitch = bpp * w;
if (pitch != tightened_pitch) {
/* There is extra padding that we need to get rid of, if we don't
* do this the miniz backend is going to generate corrupt PNGs */
Uint8 *tightened_pixels = SDL_malloc(tightened_pitch * h);
if (tightened_pixels) {
for (int y = 0; y < h; y++) {
SDL_memcpy(tightened_pixels + y * tightened_pitch, pixels + y * pitch, tightened_pitch);
}
png = tdefl_write_image_to_png_file_in_memory(tightened_pixels, w, h, bpp, tightened_pitch, &size);
SDL_free(tightened_pixels);
}
} else {
png = tdefl_write_image_to_png_file_in_memory(pixels, w, h, bpp, pitch, &size);
}
}
if (cvt) {
SDL_FreeSurface(cvt);
}

if (png) {
if (SDL_RWwrite(dst, png, size, 1)) {
result = 0;
Expand Down
Loading