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clipping.go
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clipping.go
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package fauxgl
var clipPlanes = []clipPlane{
{VectorW{1, 0, 0, 1}, VectorW{-1, 0, 0, 1}},
{VectorW{-1, 0, 0, 1}, VectorW{1, 0, 0, 1}},
{VectorW{0, 1, 0, 1}, VectorW{0, -1, 0, 1}},
{VectorW{0, -1, 0, 1}, VectorW{0, 1, 0, 1}},
{VectorW{0, 0, 1, 1}, VectorW{0, 0, -1, 1}},
{VectorW{0, 0, -1, 1}, VectorW{0, 0, 1, 1}},
}
type clipPlane struct {
P, N VectorW
}
func (p clipPlane) pointInFront(v VectorW) bool {
return v.Sub(p.P).Dot(p.N) > 0
}
func (p clipPlane) intersectSegment(v0, v1 VectorW) VectorW {
u := v1.Sub(v0)
w := v0.Sub(p.P)
d := p.N.Dot(u)
n := -p.N.Dot(w)
return v0.Add(u.MulScalar(n / d))
}
func sutherlandHodgman(points []VectorW, planes []clipPlane) []VectorW {
output := points
for _, plane := range planes {
input := output
output = nil
if len(input) == 0 {
return nil
}
s := input[len(input)-1]
for _, e := range input {
if plane.pointInFront(e) {
if !plane.pointInFront(s) {
x := plane.intersectSegment(s, e)
output = append(output, x)
}
output = append(output, e)
} else if plane.pointInFront(s) {
x := plane.intersectSegment(s, e)
output = append(output, x)
}
s = e
}
}
return output
}
func ClipTriangle(t *Triangle) []*Triangle {
w1 := t.V1.Output
w2 := t.V2.Output
w3 := t.V3.Output
p1 := w1.Vector()
p2 := w2.Vector()
p3 := w3.Vector()
points := []VectorW{w1, w2, w3}
newPoints := sutherlandHodgman(points, clipPlanes)
var result []*Triangle
for i := 2; i < len(newPoints); i++ {
b1 := Barycentric(p1, p2, p3, newPoints[0].Vector())
b2 := Barycentric(p1, p2, p3, newPoints[i-1].Vector())
b3 := Barycentric(p1, p2, p3, newPoints[i].Vector())
v1 := InterpolateVertexes(t.V1, t.V2, t.V3, b1)
v2 := InterpolateVertexes(t.V1, t.V2, t.V3, b2)
v3 := InterpolateVertexes(t.V1, t.V2, t.V3, b3)
result = append(result, NewTriangle(v1, v2, v3))
}
return result
}
func ClipLine(l *Line) *Line {
// TODO: interpolate vertex attributes when clipped
w1 := l.V1.Output
w2 := l.V2.Output
for _, plane := range clipPlanes {
f1 := plane.pointInFront(w1)
f2 := plane.pointInFront(w2)
if f1 && f2 {
continue
} else if f1 {
w2 = plane.intersectSegment(w1, w2)
} else if f2 {
w1 = plane.intersectSegment(w2, w1)
} else {
return nil
}
}
v1 := l.V1
v2 := l.V2
v1.Output = w1
v2.Output = w2
return NewLine(v1, v2)
}