126664 2014-01-08 14:01:04 -0800 Subpixel layout: LayoutUnit::fromFloatFloor needs flooring the CSS pixel value. 2014-01-14 15:53:02 -0800 1 1 1 Unclassified WebKit Layout and Rendering 528+ (Nightly build) Unspecified Unspecified RESOLVED INVALID InRadar P2 Normal --- 126283 1 zalan zalan jonlee simon.fraser webkit-bug-importer oldest_to_newest 965632 0 zalan 2014-01-08 14:01:04 -0800 HitTestLocation operates on flooredLayoutPoint which calls fromFloatFloor() to floor the LayoutUnit values. This produces different values when subpixel is on and may result in hitting different part of the document . failed case: (hittesting on a transformed render layer's content) fast/html/regions/overflow-region-transform.html 965662 1 simon.fraser 2014-01-08 15:32:05 -0800 fast/regions/overflow-region-transform.html 965668 2 simon.fraser 2014-01-08 15:46:21 -0800 Needs some debugging to see what the issues are. 967903 3 webkit-bug-importer 2014-01-14 10:26:00 -0800 <rdar://problem/15815563> 968076 4 zalan 2014-01-14 15:52:45 -0800 the current behavior is correct as snapping any user generated input (even after a transform) would generate false results. 1. user clicks at position x,y 2. after applying the render transform, it gets the value of 11.6px float. 3. the pixelsnaped value is -> 12(*64)=768, while normal rounding value is -> round(11.6*64)=742. 4. This pixelsnapped value would make the hittest code find the layer painted at 768/64=12px, while the user clicked at 11.6px (after transform)