SDL_SaveBMP makes .bmp files Apple Preview can't handle.

[icculus]

The example code I wrote for #11776 calls SDL_SaveBMP(), but macOS doesn't like the resulting file when you double-click it in the Finder:

GIMP on macOS opened it just fine.

Here's the actual file (zipped to make GitHub happy)...

framebuffer-bmp.zip

I thought it was the pixel format (RGBA8888), but if I export the file from GIMP like this...

...then macOS opens it just fine.

Notable output from the file command on the bmp that Preview doesn't like...

$ file render-target.bmp
render-target.bmp: PC bitmap, Windows 95/NT4 and newer format, 640 x 480 x 32, cbSize 1228922, bits offset 122

...vs the converted GIMP file...

$ file render-target.bmp
render-target.bmp: PC bitmap, Windows 98/2000 and newer format, 640 x 480 x 32, cbSize 1228938, bits offset 138

This works with SDL_SaveBMP if I convert the file to SDL_PIXELFORMAT_RGB565 first, so it's not just SDL_SaveBMP is totally busted across the board...

SDL_Surface *cvt = SDL_ConvertSurface(surface, SDL_PIXELFORMAT_RGB565);
SDL_SaveBMP(cvt, fname);

The file info for that...

$ file render-target.bmp
render-target.bmp: PC bitmap, Windows 3.x format, 640 x 480 x 24, image size 921600, cbSize 921654, bits offset 54

[icculus]

Won't open RGBA8888, BGRA8888, ARGB8888, nor ABGR8888 either.

[superzazu]

Hello!

Not sure if this is the same problem, but I’ve had a similar problem and the only workaround I found was:

SDL_SetHint(SDL_HINT_BMP_SAVE_LEGACY_FORMAT, "1");

https://github.com/superzazu/SMGF/blob/bbcf27170f990edc0416583ff65a8c4e0b80a024/src/main.c#L248

Hope this helps,
Have a good day

[icculus]

Huh, yeah, it looks like Preview doesn't like the version 4 headers.

But Gimp could write a 32-bit bmp that it liked, so our assertion that you need the version 4 headers to write a 32-bit bitmap isn't true, but I haven't looked further yet.