vector: Add Arc

Updates #844
This commit is contained in:
Hajime Hoshi 2021-07-17 01:29:41 +09:00
parent 873bb35587
commit 70ef5e7d5b
2 changed files with 58 additions and 4 deletions

View File

@ -168,11 +168,15 @@ func drawArc(screen *ebiten.Image, count int) {
path.MoveTo(350, 100)
const cx, cy, r = 450, 100, 70
theta := math.Pi * float64(count) / 180
x := cx + r*math.Cos(theta)
y := cy + r*math.Sin(theta)
theta1 := math.Pi * float64(count) / 180
x := cx + r*math.Cos(theta1)
y := cy + r*math.Sin(theta1)
path.ArcTo(450, 100, float32(x), float32(y), 30)
theta2 := math.Pi * float64(count) / 180 / 3
path.MoveTo(550, 100)
path.Arc(550, 100, 50, float32(theta1), float32(theta2))
op := &ebiten.DrawTrianglesOptions{
EvenOdd: true,
}

View File

@ -45,7 +45,9 @@ func (p *Path) MoveTo(x, y float32) {
// LineTo updates the current position to (x, y).
func (p *Path) LineTo(x, y float32) {
if len(p.segs) == 0 {
p.segs = append(p.segs, []point{p.cur})
p.segs = append(p.segs, []point{{x: x, y: y}})
p.cur = point{x: x, y: y}
return
}
seg := p.segs[len(p.segs)-1]
if seg[len(seg)-1].x != x || seg[len(seg)-1].y != y {
@ -182,6 +184,54 @@ func (p *Path) ArcTo(x1, y1, x2, y2, radius float32) {
p.LineTo(x2, y2)
}
// Arc adds an arc to the path.
// (x, y) is the center of the arc.
//
// Arc updates the current position to the end of the arc.
func (p *Path) Arc(x, y, radius, startAngle, endAngle float32) {
// Adjust the angles.
for startAngle > endAngle {
endAngle += 2 * math.Pi
}
da := float64(endAngle - startAngle)
if da >= 2*math.Pi {
da = 2 * math.Pi
endAngle = startAngle + float32(da)
}
// If the angle is big, splict this into multiple Arc calls.
if da > math.Pi/2 {
const delta = math.Pi / 3
a := float64(startAngle)
for {
p.Arc(x, y, radius, float32(a), float32(math.Min(a+delta, float64(endAngle))))
if a+delta >= float64(endAngle) {
break
}
a += delta
}
return
}
sin0, cos0 := math.Sincos(float64(startAngle))
x0 := x + radius*float32(cos0)
y0 := y + radius*float32(sin0)
sin1, cos1 := math.Sincos(float64(endAngle))
x1 := x + radius*float32(cos1)
y1 := y + radius*float32(sin1)
p.LineTo(x0, y0)
// Calculate the control points for an approximated Bézier curve.
// See https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/graphics/skiasharp/curves/beziers.
l := radius * float32(math.Tan(da/4)*4/3)
cx0 := x0 + l*float32(-sin0)
cy0 := y0 + l*float32(cos0)
cx1 := x1 + l*float32(sin1)
cy1 := y1 + l*float32(-cos1)
p.CubicTo(cx0, cy0, cx1, cy1, x1, y1)
}
// AppendVerticesAndIndicesForFilling appends vertices and indices to fill this path and returns them.
// AppendVerticesAndIndicesForFilling works in a similar way to the built-in append function.
// If the arguments are nils, AppendVerticesAndIndices returns new slices.