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Bug 2014 - Hardcoded srcA value in SDL_Blit_RGB888_RGB888_Blend_Scale function
Summary: Hardcoded srcA value in SDL_Blit_RGB888_RGB888_Blend_Scale function
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: video (show other bugs)
Version: 2.0.0
Hardware: x86 Linux
: P2 normal
Assignee: Sam Lantinga
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2013-08-06 02:47 UTC by Nitz
Modified: 2019-10-24 16:14 UTC (History)
1 user (show)

See Also:

Attachments
patch (18.62 KB, patch)
2017-10-24 20:22 UTC, Sylvain 		Details | Diff
View All Add an attachment (proposed patch, testcase, etc.)

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Description Nitz 2013-08-06 02:47:43 UTC 
In Function
static void SDL_Blit_RGB888_RGB888_Blend_Scale(SDL_BlitInfo *info)
{
  // Some Code
  srcR = (Uint8)(srcpixel >> 16); srcG = (Uint8)(srcpixel >> 8); srcB = (Uint8)srcpixel; srcA = 0xFF;
  
  dstpixel = *dst;
  
  dstR = (Uint8)(dstpixel >> 16); dstG = (Uint8)(dstpixel >> 8); dstB = (Uint8)dstpixel; dstA = 0xFF;
            
  if (flags & (SDL_COPY_BLEND|SDL_COPY_ADD)) {
  /* This goes away if we ever use premultiplied alpha */
   if (srcA < 255) {
    srcR = (srcR * srcA) / 255;
    srcG = (srcG * srcA) / 255;
    srcB = (srcB * srcA) / 255;
   }
  }

 //Some Code
}

In this code srcA and dstA value is hardcoded to 0xFF, because of which the if condition 
if (srcA < 255) {
    srcR = (srcR * srcA) / 255;
    srcG = (srcG * srcA) / 255;
    srcB = (srcB * srcA) / 255;
   }
will never get executed.
So either remove this code or change the hardcoded value of srcA and dstA.

Thanks!
Comment 1 Sylvain 2017-10-24 20:22:40 UTC 
Created attachment 3041 [details]
patch

not fully tested, but here's a patch to remove hardcoded constants.
Comment 2 Sylvain 2019-10-24 16:08:02 UTC 
Fixed in https://hg.libsdl.org/SDL/rev/f530cdaaab62
Comment 3 Sylvain 2019-10-24 16:14:09 UTC 
Modified sdlgenblit.pl so that when:
srcA = 0xFF;
or
A = 0xFF;
It is initialised as const and/or inlined afterwards. 
Un-reacheable code is removed !