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Bug 3889

Summary: please allow for paletted surfaces with 32 bit depth
Product: SDL Reporter: Fabian Greffrath <fabian+debian>
Component: videoAssignee: Sam Lantinga <slouken>
Status: WAITING --- QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2    
Version: HG 2.0   
Hardware: x86   
OS: Windows 7   

Description Fabian Greffrath 2017-10-16 11:09:56 UTC 
Hi there,

as the API documentation for SDL_CreateRGBSurface() states "If depth is 4 or 8 bits, an empty palette is allocated for the surface. If depth is greater than 8 bits, the pixel format is set using the [RGBA]mask parameters."

However, I would like to create a surface with a 32-bit palette. Why? Because I am creating a source port for Doom, which usually uses a 256-color palette stored in a single byte per color. I want to extend the game to optional true-color rendering and will thus have to change the framebuffer to a 32-bit surface. In order to prevent the need to completely reimplement each rendering routine, I would like to increase the default framebuffer to 32-bit per pixel and interpret each pixel value as a palette index in "paletted" mode and as a RGBA tupel in "true-color" mode. However, with the current limitations on SDL_CreateRGBSurface() this seems impossible to achieve.

Please consider allowing for 32-bit paletted surfaces, thanks!

 - Fabian
Comment 1 Sam Lantinga 2017-10-16 18:19:14 UTC 
I'm fine with that, but it would be a feature of SDL_Surface, not the rendering system.

Would you like to attach a tested patch?
Comment 2 Fabian Greffrath 2017-10-17 10:29:33 UTC 
(In reply to Sam Lantinga from comment #1)
> Would you like to attach a tested patch?

I am not yet that far, just sharing the idea.
Comment 3 Sam Lantinga 2017-10-17 15:45:45 UTC 
Okay, that would be fine with me. :)
Comment 4 Sam Lantinga 2017-10-17 15:47:13 UTC 
Once you implement a patch you might want to check the performance. Shuffling around 32-bit data might be more expensive than working with 8-bit data and doing a final 32-bit expansion right before rendering.
Comment 5 Fabian Greffrath 2018-08-15 21:55:17 UTC 
This seems to be a lot more involved than I initially expected/hoped. There are assumptions about palette values being Uint8 all over the code.

However, I was pleasantly surprised that simply changing code from this

screenbuffer = SDL_CreateRGBSurface(0, SCREENWIDTH, SCREENHEIGHT, 8, 0, 0, 0, 0);

to this

screenbuffer = SDL_CreateRGBSurface(0, SCREENWIDTH, SCREENHEIGHT, 32, 0, 0, 0, 0);
SDL_Palette *palette = SDL_AllocPalette(256);
SDL_SetSurfacePalette(screenbuffer, palette);
SDL_FreePalette(palette);

does at least not crash, but then each paletted image will be displayed as shades of blue.