[Webkit-unassigned] [Bug 62141] New: Incorrect interpolation of color values in transitions

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=62141

           Summary: Incorrect interpolation of color values in transitions
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: bzbarsky at mit.edu


Created an attachment (id=96114)
 --> (https://bugs.webkit.org/attachment.cgi?id=96114&action=review)
Testcase

BUILD: Current WebKit nightly (or current Chrome dev)

STEPS TO REPRODUCE:
1)  Load attached testcase.
2)  Examine the sum of the "r" and "b" values in the printed rgb() triplets.

EXPECTED RESULTS: Sum is always 255.

ACTUAL RESULTS: Sum is 254 for most of them.

ADDITIONAL NOTES: This is a regression from Safari 5.

To see why the expected results are expected, note that at time t/5s in the range [0, 1] in the transition the computed color should be:

  rgb(255*(1-t), 0, 255*t);

Now the color components will be rounded, but, for example, if 255*(1-t) is rounding to 254 then 255*t > 0.5.  And therefore 255*t should be rounding to 1, not to 0.

It looks like WebKit is just truncating the floating-point color values to get the interpolated color value instead of correctly rounding.

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