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op/clip: introduce axis-aligned Ellipse shape

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And deprecate (but not yet remove) Circle.

Signed-off-by: Elias Naur <mail@eliasnaur.com>
This commit is contained in:
Elias Naur
2021-10-25 17:38:04 +02:00
parent 1d0769ae89
commit 28fc08a508
1 changed files with 44 additions and 13 deletions
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op/clip/shapes.go
+44 -13
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@@ -114,7 +114,7 @@ type Circle struct {
Radius float32
}
// Op returns the op for the circle.
// Op returns the op for the filled circle.
func (c Circle) Op(ops *op.Ops) Op {
return Outline{Path: c.Path(ops)}.Op()
}
@@ -125,38 +125,69 @@ func (c Circle) Push(ops *op.Ops) Stack {
}
// Path returns the PathSpec for the circle.
//
// Deprecated: use Ellipse instead.
func (c Circle) Path(ops *op.Ops) PathSpec {
b := f32.Rectangle{
Min: f32.Pt(c.Center.X-c.Radius, c.Center.Y-c.Radius),
Max: f32.Pt(c.Center.X+c.Radius, c.Center.Y+c.Radius),
}
return Ellipse{b}.Path(ops)
}
// Ellipse represents the largest axis-aligned ellipse that
// is contained in its bounds.
type Ellipse struct {
Bounds f32.Rectangle
}
// Op returns the op for the filled ellipse.
func (e Ellipse) Op(ops *op.Ops) Op {
return Outline{Path: e.Path(ops)}.Op()
}
// Push the filled ellipse clip op on the clip stack.
func (e Ellipse) Push(ops *op.Ops) Stack {
return e.Op(ops).Push(ops)
}
// Path constructs a path for the ellipse.
func (e Ellipse) Path(ops *op.Ops) PathSpec {
var p Path
p.Begin(ops)
center := c.Center
r := c.Radius
center := e.Bounds.Max.Add(e.Bounds.Min).Mul(.5)
diam := e.Bounds.Dx()
r := diam * .5
// We'll model the ellipse as a circle scaled in the Y
// direction.
scale := e.Bounds.Dy() / diam
// https://pomax.github.io/bezierinfo/#circles_cubic.
const q = 4 * (math.Sqrt2 - 1) / 3
curve := r * q
top := f32.Point{X: center.X, Y: center.Y - r}
top := f32.Point{X: center.X, Y: center.Y - r*scale}
p.MoveTo(top)
p.CubeTo(
f32.Point{X: center.X + curve, Y: center.Y - r},
f32.Point{X: center.X + r, Y: center.Y - curve},
f32.Point{X: center.X + curve, Y: center.Y - r*scale},
f32.Point{X: center.X + r, Y: center.Y - curve*scale},
f32.Point{X: center.X + r, Y: center.Y},
)
p.CubeTo(
f32.Point{X: center.X + r, Y: center.Y + curve},
f32.Point{X: center.X + curve, Y: center.Y + r},
f32.Point{X: center.X, Y: center.Y + r},
f32.Point{X: center.X + r, Y: center.Y + curve*scale},
f32.Point{X: center.X + curve, Y: center.Y + r*scale},
f32.Point{X: center.X, Y: center.Y + r*scale},
)
p.CubeTo(
f32.Point{X: center.X - curve, Y: center.Y + r},
f32.Point{X: center.X - r, Y: center.Y + curve},
f32.Point{X: center.X - curve, Y: center.Y + r*scale},
f32.Point{X: center.X - r, Y: center.Y + curve*scale},
f32.Point{X: center.X - r, Y: center.Y},
)
p.CubeTo(
f32.Point{X: center.X - r, Y: center.Y - curve},
f32.Point{X: center.X - curve, Y: center.Y - r},
f32.Point{X: center.X - r, Y: center.Y - curve*scale},
f32.Point{X: center.X - curve, Y: center.Y - r*scale},
top,
)
return p.End()