// ScreenTransf returns a new matrix that transforms vectors after projection
// to screen coordinates. The upper left corner of the near rectangle will be
// (0,0) and the bottom right will be (w,h). If the aspect ratio does not match
// the camera the image will be distorted.
func ScreenTransf(f *Frustum, w, h int) *geom.Mat4 {
wf := float64(w)
hf := float64(h)
t := TranslTransf(&geom.Vec3{f.Nwidth / 2, -f.Nheight / 2, 0})
m := geom.Mat4{
wf / f.Nwidth, 0, 0, 0,
0, -hf / f.Nheight, 0, 0,
0, 0, 1, 0,
0, 0, 0, 1,
}
m.Mul(t)
return &m
}
// Transf transforms a 3D triangle with the given transformation matrix and
// returns a 2D triangle.
func (t *Tri4) Transf(m *geom.Mat4) *Tri2 {
p1 := m.Transf(&t[0])
x1 := tmath.Round(p1[0] / p1[3])
y1 := tmath.Round(p1[1] / p1[3])
p2 := m.Transf(&t[1])
x2 := tmath.Round(p2[0] / p2[3])
y2 := tmath.Round(p2[1] / p2[3])
p3 := m.Transf(&t[2])
x3 := tmath.Round(p3[0] / p3[3])
y3 := tmath.Round(p3[1] / p3[3])
return NewTri2(x1, y1, x2, y2, x3, y3)
}