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Bug 2639 - SDL_BLENDMODE_BLEND not working properly for software renderer
Summary: SDL_BLENDMODE_BLEND not working properly for software renderer
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: render (show other bugs)
Version: HG 2.0
Hardware: x86_64 Linux
: P2 normal
Assignee: Sam Lantinga
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2014-07-12 19:40 UTC by Damian Kaczmarek
Modified: 2014-07-12 23:22 UTC (History)
1 user (show)

See Also:

Attachments
Source coding showing the problem (2.79 KB, text/x-c++src)
2014-07-12 19:40 UTC, Damian Kaczmarek 		Details
software blending patch (712 bytes, patch)
2014-07-12 20:57 UTC, Melker Narikka 		Details | Diff
software blending patch - non-eaten version (660 bytes, patch)
2014-07-12 21:04 UTC, Melker Narikka 		Details | Diff
software blending patch - v2 (679 bytes, patch)
2014-07-12 22:01 UTC, Melker Narikka 		Details | Diff
Updated test code (3.10 KB, text/x-c++src)
2014-07-12 22:29 UTC, Damian Kaczmarek 		Details
software blending patch - v3 (335 bytes, patch)
2014-07-12 23:01 UTC, Melker Narikka 		Details | Diff
Show Obsolete (4) View All Add an attachment (proposed patch, testcase, etc.)

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Description Damian Kaczmarek 2014-07-12 19:40:34 UTC 
Created attachment 1742 [details]
Source coding showing the problem

I attach a program showing the problem. 

g++ sdl2bug.cpp -lSDL2 && ./a.out

Window on the right shows software renderer which is wrong
Window on the left shows hardware renderer which is right

I would also appreciate suggestions if there are possible workarounds
Comment 1 Damian Kaczmarek 2014-07-12 19:46:05 UTC 
I should also add that setting render mode does not fail.
Comment 2 Sam Lantinga 2014-07-12 20:08:00 UTC 
Great bug report, I'll look into it.

Thanks!
Comment 3 Melker Narikka 2014-07-12 20:57:22 UTC 
Created attachment 1743 [details]
software blending patch

Does this patch help?
Comment 4 Melker Narikka 2014-07-12 21:04:39 UTC 
Created attachment 1744 [details]
software blending patch - non-eaten version

Oops, bugzilla ate the patch headers :(
Comment 5 Damian Kaczmarek 2014-07-12 21:08:25 UTC 
I applied the patch manually and it works! Thanks!
Comment 7 Melker Narikka 2014-07-12 22:01:42 UTC 
Created attachment 1745 [details]
software blending patch - v2

Here's an updated patch. Does it make a difference?
Comment 8 Damian Kaczmarek 2014-07-12 22:29:55 UTC 
Created attachment 1746 [details]
Updated test code

Added a semi-transparent green rectangle being blended, again this shows different results from software and hardware renderers
Comment 9 Damian Kaczmarek 2014-07-12 22:30:41 UTC 
Otherwise your latest patch fixes the most obvious problems, we're getting there! Good work.
Comment 10 Melker Narikka 2014-07-12 23:01:06 UTC 
Created attachment 1747 [details]
software blending patch - v3

Okay, let's try that again, shall we? This one only touches the alpha, and seems to act right with the updated test case.
Comment 11 Damian Kaczmarek 2014-07-12 23:10:07 UTC 
Seems to work perfectly, thank you!
Comment 12 Sam Lantinga 2014-07-12 23:12:48 UTC 
Does this work?
sa = DRAW_MUL(inva, sa) + a;
Comment 13 Melker Narikka 2014-07-12 23:14:14 UTC 
(In reply to Sam Lantinga from comment #12)
> Does this work?
> sa = DRAW_MUL(inva, sa) + a;

v3 does just that :)
Comment 14 Sam Lantinga 2014-07-12 23:15:04 UTC 
Yeah, I just wanted to see if ordering mattered, for consistency with the previous lines.
Comment 15 Damian Kaczmarek 2014-07-12 23:16:05 UTC 
It works quite fine.
Comment 16 Sam Lantinga 2014-07-12 23:22:30 UTC 
Fixed, thanks!
https://hg.libsdl.org/SDL/rev/515be38f3f37