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Bug 2352

Summary: SDL_SetTextureAlphaMod doesn't work on textures without a image-side alpha channel
Product: SDL Reporter: c4577894
Component: videoAssignee: Sam Lantinga <slouken>
Status: RESOLVED INVALID QA Contact: Sam Lantinga <slouken>
Severity: major    
Priority: P2 CC: adam
Version: 2.0.1   
Hardware: x86_64   
OS: Windows 7   

Description c4577894 2014-01-18 07:13:21 UTC 
Using SDL_SetTextureAlphaMod on a texture that doesn't have an alpha channel will do nothing, it doesn't return anything you can check with SDL_GetError either.

Tried it with .jpgs, .bmps and .pngs, none of them work.

Same result on DirectX, OpenGL and Software renderer.
Comment 1 Adam M. 2014-05-11 01:36:21 UTC 
That's really unfortunate. It seems to me that one of the main points of SDL_SetTextureAlphaMod is to allow alpha blending surfaces that don't have their own alpha channel.
Comment 2 Adam M. 2014-05-11 19:54:01 UTC 
I haven't been able to reproduce this behavior in the software renderer (using 16-bit textures w/o an alpha channel).

You have to set the texture blend mode before it will work, in addition to setting the texture alpha mod:

SDL_SetTextureBlendMode(hTexture, SDL_BLENDMODE_BLEND);

Does that help?
Comment 3 Sam Lantinga 2017-08-14 10:33:47 UTC 
Adam, I think you're right, SDL_SetTextureBlendMode() was missing.