[Webkit-unassigned] [Bug 80806] New: [chromium] Need to implement real actual geometric clipping.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=80806

           Summary: [chromium] Need to implement real actual geometric
                    clipping.
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: shawnsingh at chromium.org
                CC: shawnsingh at chromium.org
            Blocks: 74147,79136


WebCore TransformationMatrix does not properly handle un-projecting from a perspective transform, for surfaces where at least one of its vertices is behind the camera.

But it is not as simple as "handling this case properly" because there really isn't a good way to handle it.  (refer to http://dl.acm.org/citation.cfm?id=807398 to understand why)  The real need is to clip geometry that goes behind the camera so that we never try to un-project vertices that are behind the camera.  However, this can create triangles, pentagons, or other general polygons depending on what we need to clip.

This patch will first implement clipping in chromium, to get some rendering bugs fixed (for example, http://code.google.com/p/chromium/issues/detail?id=105100 among others).  Later we will try to migrate the correct clipping to WebCore to fix problems for hit testing bugs (for example, https://bugs.webkit.org/show_bug.cgi?id=79136 among others).

One question that might come up is "why doesn't this affect rendering for Safari?" -- the answer is that Safari, as far as I know, doesn't use projectQuad in its compositor.  But the hit testing bugs do indeed affect both Safari and Chromium.

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