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vector: add more comments

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Hajime Hoshi
2025-07-07 14:25:42 +09:00
parent 6408f40a7f
commit 7eaa1fdcdb
1 changed files with 7 additions and 0 deletions
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vector/path.go
+7
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@@ -591,6 +591,13 @@ func (p *Path) ArcTo(x1, y1, x2, y2, radius float32) {
// A cross product can be calculated by d0.x*d1.y - d0.y*d1.x,
// but this can cause a floating-point precision issue due to FMSUBS.
// Avoid this subtraction.
//
// a*b - c*d can be translated into
// (1) x := c*d
// (2) y := a*b-x
// One rounding happens at (1). The number of rounding is not determined at (2).
// If FMSUBS is used for (2), only one rounding happens at (2) for the multiplying and the subtraction.
// Thus, even if a*b == c*d, y can be non-zero.
if d0.x*d1.y >= d0.y*d1.x {
cx = ax0 - d0.y*radius
cy = ay0 + d0.x*radius