[Webkit-unassigned] [Bug 105650] New: Quadratic and bezier curves with coincident endpoints rendered incorrectly

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=105650

           Summary: Quadratic and bezier curves with coincident endpoints
                    rendered incorrectly
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Canvas
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: kbr at google.com
                CC: simon.fraser at apple.com, dino at apple.com,
                    senorblanco at chromium.org, junov at google.com


CanvasRenderingContext2D::quadraticCurveTo and bezierCurveTo contain incorrect optimizations which skip adding the incoming curve if its endpoint is the same as the path's current point. It is easy to construct a Bezier curve with coincident endpoints and non-zero area by moving its control points; similarly, a degenerate quadratic curve with coincident endpoints but a different control point should be rendered as a line. The attached test case from https://code.google.com/p/chromium/issues/detail?id=160277 shows the problem for bezier curves, but the same problem exists for quadratic curves.

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