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Bug 1933668 - Undo half-pixel shift from WGR when using AA-Stroke. r=aosmond, a=RyanVM

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Differential Revision: https://phabricator.services.mozilla.com/D231471
This commit is contained in:
Lee Salzman 2024-12-07 19:32:02 +00:00
parent 35cb3165a6
commit 13f41c6ec4
1 changed files with 6 additions and 1 deletions
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7
dom/canvas/DrawTargetWebgl.cpp
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@ -3048,7 +3048,12 @@ static inline AAStroke::LineCap ToAAStrokeLineCap(CapStyle aCap) {
}
static inline Point WGRPointToPoint(const WGR::Point& aPoint) {
return Point(IntPoint(aPoint.x, aPoint.y)) * (1.0f / 16.0f);
// WGR points are 28.4 fixed-point where (0.0, 0.0) is assumed to be a pixel
// center, as opposed to (0.5, 0.5) in canvas device space. WGR thus shifts
// each point by (-0.5, -0.5). To undo this, transform from fixed-point back
// to floating-point, and reverse the pixel shift by adding back (0.5, 0.5).
return Point(IntPoint(aPoint.x, aPoint.y)) * (1.0f / 16.0f) +
Point(0.5f, 0.5f);
}
// Generates a vertex buffer for a stroked path using aa-stroke.