97 lines
2 KiB
Go
97 lines
2 KiB
Go
package canvas
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import (
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"github.com/tfriedel6/lm"
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)
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func pointIsRightOfLine(a, b, p lm.Vec2) bool {
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if a[1] == b[1] {
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return false
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}
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if a[1] > b[1] {
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a, b = b, a
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}
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if p[1] < a[1] || p[1] > b[1] {
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return false
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}
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v := b.Sub(a)
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r := (p[1] - a[1]) / v[1]
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x := a[0] + r*v[0]
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return p[0] > x
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}
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func triangleContainsPoint(a, b, c, p lm.Vec2) bool {
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// if point is outside triangle bounds, return false
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if p[0] < a[0] && p[0] < b[0] && p[0] < c[0] {
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return false
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}
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if p[0] > a[0] && p[0] > b[0] && p[0] > c[0] {
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return false
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}
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if p[1] < a[1] && p[1] < b[1] && p[1] < c[1] {
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return false
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}
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if p[1] > a[1] && p[1] > b[1] && p[1] > c[1] {
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return false
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}
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// check whether the point is to the right of each triangle line.
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// if the total is 1, it is inside the triangle
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count := 0
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if pointIsRightOfLine(a, b, p) {
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count++
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}
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if pointIsRightOfLine(b, c, p) {
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count++
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}
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if pointIsRightOfLine(c, a, p) {
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count++
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}
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return count == 1
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}
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func polygonContainsPoint(polygon []lm.Vec2, p lm.Vec2) bool {
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a := polygon[len(polygon)-1]
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count := 0
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for _, b := range polygon {
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if pointIsRightOfLine(a, b, p) {
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count++
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}
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a = b
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}
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return count%2 == 1
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}
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func triangulatePath(path []pathPoint, target []float32) []float32 {
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var buf [500]lm.Vec2
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polygon := buf[:0]
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for _, p := range path {
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polygon = append(polygon, p.pos)
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}
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for len(polygon) > 2 {
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var i int
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triangles:
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for i = range polygon {
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a := polygon[i]
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b := polygon[(i+1)%len(polygon)]
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c := polygon[(i+2)%len(polygon)]
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for i2, p := range polygon {
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if i2 >= i && i2 <= i+2 {
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continue
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}
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if triangleContainsPoint(a, b, c, p) {
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continue triangles
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}
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center := a.Add(b).Add(c).DivF(3)
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if !polygonContainsPoint(polygon, center) {
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continue triangles
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}
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}
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target = append(target, a[0], a[1], b[0], b[1], c[0], c[1])
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break
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}
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remove := (i + 1) % len(polygon)
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polygon = append(polygon[:remove], polygon[remove+1:]...)
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}
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return target
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}
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