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Bug 2014

Summary: Hardcoded srcA value in SDL_Blit_RGB888_RGB888_Blend_Scale function
Product: SDL Reporter: Nitz <nitin.j4>
Component: videoAssignee: Sam Lantinga <slouken>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: sylvain.becker
Version: 2.0.0   
Hardware: x86   
OS: Linux   
Attachments: patch

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 !