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geometryUtils.go
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geometryUtils.go
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package assets
import (
"github.com/go-gl/mathgl/mgl32"
"github.com/walesey/go-engine/renderer"
"github.com/walesey/go-engine/util"
)
// IntersectGeometry - returns a list of line segments resulting from the xz plane intersection of the geometry
func IntersectGeometry(geometry *renderer.Geometry) [][2]mgl32.Vec2 {
segments := make([][2]mgl32.Vec2, 0)
for i := 0; i < len(geometry.Indicies); i = i + 3 {
index := geometry.Indicies[i]
v1 := mgl32.Vec3{geometry.Verticies[index*renderer.VertexStride], geometry.Verticies[index*renderer.VertexStride+1], geometry.Verticies[index*renderer.VertexStride+2]}
index = geometry.Indicies[i+1]
v2 := mgl32.Vec3{geometry.Verticies[index*renderer.VertexStride], geometry.Verticies[index*renderer.VertexStride+1], geometry.Verticies[index*renderer.VertexStride+2]}
index = geometry.Indicies[i+2]
v3 := mgl32.Vec3{geometry.Verticies[index*renderer.VertexStride], geometry.Verticies[index*renderer.VertexStride+1], geometry.Verticies[index*renderer.VertexStride+2]}
va, vb, vc := v1, v2, v3
if (v1.Y() < 0 && v2.Y() > 0 && v3.Y() > 0) || (v1.Y() > 0 && v2.Y() < 0 && v3.Y() < 0) {
va, vb, vc = v1, v2, v3
} else if (v1.Y() > 0 && v2.Y() < 0 && v3.Y() > 0) || (v1.Y() < 0 && v2.Y() > 0 && v3.Y() < 0) {
va, vb, vc = v2, v1, v3
} else if (v1.Y() > 0 && v2.Y() > 0 && v3.Y() < 0) || (v1.Y() < 0 && v2.Y() < 0 && v3.Y() > 0) {
va, vb, vc = v3, v2, v1
} else {
continue
}
t_ab := -va.Y() / (va.Y() - vb.Y())
t_ac := -va.Y() / (va.Y() - vc.Y())
segments = append(segments, [2]mgl32.Vec2{
mgl32.Vec2{va.X() + (va.X()-vb.X())*t_ab, va.Z() + (va.Z()-vb.Z())*t_ab},
mgl32.Vec2{va.X() + (va.X()-vc.X())*t_ac, va.Z() + (va.Z()-vc.Z())*t_ac},
})
}
return segments
}
// Converts a geometry directly into points (does threshold culling optimisation)
func PointsFromGeometry(geometry *renderer.Geometry, cullThreshold float32) *[]mgl32.Vec3 {
verticies := make([]mgl32.Vec3, 0, len(geometry.Indicies))
for i := 0; i < len(geometry.Indicies); i = i + 1 {
index := geometry.Indicies[i]
v := mgl32.Vec3{
geometry.Verticies[index*renderer.VertexStride],
geometry.Verticies[index*renderer.VertexStride+1],
geometry.Verticies[index*renderer.VertexStride+2],
}
//do culling
include := true
for _, vert := range verticies {
if util.Vec3LenSq(vert.Sub(v)) < cullThreshold*cullThreshold {
include = false
break
}
}
if include {
verticies = append(verticies, v)
}
}
return &verticies
}