[Webkit-unassigned] [Bug 86026] [QT 32 bit] Child div overlay on parent div results in image diff when it shouldn't

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=86026





--- Comment #6 from Dave Tharp <dtharp at codeaurora.org>  2012-05-10 09:28:12 PST ---
More research on this issue:

I have analyzed the actual vs expected output with "compare -verbose -identify". The interesting part is the histogram and the resultant diff.png.

The relevant part of the histograms:

== actual ==
  Histogram:
       296: (  0,  0,  0,255) #000000 black
     29700: (  0,128,  0,255) #008000 green
         4: (  1,  1,  1,255) #010101 rgba(1,1,1,1)
       300: (  1,127,  0,255) #017F00 rgba(1,127,0,1)
         1: (  2,  2,  2,255) #020202 rgba(2,2,2,1)

== expected == 
  Histogram:
       296: (  0,  0,  0,255) #000000 black
     30000: (  0,128,  0,255) #008000 green
         4: (  1,  1,  1,255) #010101 rgba(1,1,1,1)
         1: (  2,  2,  2,255) #020202 rgba(2,2,2,1)

Note that expected has 30,000 green pixels as expected (300 * 100). Now the actual has only 29700 green pixels. There are 300 missing, as if the child div is missing an entire line. Where are these 300 pixels? Well, there are 300 pixels that are *almost* green (1,127,0) present. This line of pixels is off by 1 bit in red and green.  The diff png (attached) shows this line as the very bottom line of the rectangle.

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