3dtrial/tinyrender5/render.go

package main

import (
// "log"
)

// Figure out the minimum bounding box for a triangle defined by
// these vertices. Returns the top left and bottom right points,
// inclusive
func ComputeBoundingBox(v0, v1, v2 Vec2i) (Vec2i, Vec2i) {
	return Vec2i{min(v0.X, v1.X, v2.X), min(v0.Y, v1.Y, v2.Y)},
		Vec2i{max(v0.X, v1.X, v2.X), max(v0.Y, v1.Y, v2.Y)}
}

// The generic edge function, returning positive if P is on the right side of
// the line drawn between v1 and v2. This is counter clockwise
func EdgeFunction(v1, v2, p Vec2f) float32 {
	return (p.X-v1.X)*(v2.Y-v1.Y) - (p.Y-v1.Y)*(v2.X-v1.X)
}

// This computes the x and y per-pixel increment for the line going
// between v1 and v2 (also counter clockwise)
func EdgeIncrement(v1, v2 Vec2f) (float32, float32) {
	return (v2.Y - v1.Y), -(v2.X - v1.X)
}

// The generic edge function, returning positive if P is on the right side of
// the line drawn between v1 and v2. This is counter clockwise
func EdgeFunctioni(v1, v2, p Vec2i) int {
	return (p.X-v1.X)*(v2.Y-v1.Y) - (p.Y-v1.Y)*(v2.X-v1.X)
}

// This computes the x and y per-pixel increment for the line going
// between v1 and v2 (also counter clockwise)
func EdgeIncrementi(v1, v2 Vec2i) (int, int) {
	return (v2.Y - v1.Y), -(v2.X - v1.X)
}

func Triangle3(fb *Framebuffer, color uint, v0f Vec3f, v1f Vec3f, v2f Vec3f) {
	v0 := v0f.ToVec2i()
	v1 := v1f.ToVec2i()
	v2 := v2f.ToVec2i()
	boundsTL, boundsBR := ComputeBoundingBox(v0, v1, v2)
	if boundsTL.Y < 0 {
		boundsTL.Y = 0
	}
	if boundsTL.X < 0 {
		boundsTL.X = 0
	}
	if boundsBR.Y >= int(fb.Height) {
		boundsBR.Y = int(fb.Height - 1)
	}
	if boundsBR.X >= int(fb.Width) {
		boundsBR.X = int(fb.Width - 1)
	}
	// Where to start our scanning
	pstart := Vec2i{boundsTL.X, boundsTL.Y}
	parea := EdgeFunctioni(v0, v1, v2)
	// if parea < 0 {
	// 	v1, v2 = v2, v1
	// 	v1f, v2f = v2f, v1f
	// 	parea = EdgeFunctioni(v0, v1, v2)
	// }
	invarea := 1 / float32(parea)
	w0_y := EdgeFunctioni(v1, v2, pstart)
	w1_y := EdgeFunctioni(v2, v0, pstart)
	w2_y := EdgeFunctioni(v0, v1, pstart)
	w0_xi, w0_yi := EdgeIncrementi(v1, v2)
	w1_xi, w1_yi := EdgeIncrementi(v2, v0)
	w2_xi, w2_yi := EdgeIncrementi(v0, v1)

	for y := uint(boundsTL.Y); y <= uint(boundsBR.Y); y++ {
		w0 := w0_y
		w1 := w1_y
		w2 := w2_y
		for x := uint(boundsTL.X); x <= uint(boundsBR.X); x++ {
			if (w0 | w1 | w2) >= 0 {
				//fb.Data[di] = color
				//done = true
				w0a := float32(w0) * invarea
				w1a := float32(w1) * invarea
				w2a := float32(w2) * invarea
				pz := uint16(w0a*v0f.Z + w1a*v1f.Z + w2a*v2f.Z)
				if pz < fb.ZBuffer[x+y*fb.Width] {
					//log.Print(pz)
					fb.ZBuffer[x+y*fb.Width] = pz
					fb.Set(x, y, color)
				}
				// fb.Set(x, y, Col2Uint(byte(255*w0a), byte(255*w1a), byte(255*w2a)))
			}
			w0 += w0_xi
			w1 += w1_xi
			w2 += w2_xi
		}
		w0_y += w0_yi
		w1_y += w1_yi
		w2_y += w2_yi
	}
}

func Triangle3t(fb *Framebuffer, texture *Framebuffer, intensity float32, v0v Vertex, v1v Vertex, v2v Vertex) {
	v0 := v0v.Pos.ToVec2i()
	v1 := v1v.Pos.ToVec2i()
	v2 := v2v.Pos.ToVec2i()
	boundsTL, boundsBR := ComputeBoundingBox(v0, v1, v2)
	if boundsBR.Y < 0 || boundsBR.X < 0 || boundsTL.X >= int(fb.Width) || boundsTL.Y >= int(fb.Height) {
		return
	}
	parea := EdgeFunctioni(v0, v1, v2)
	if parea == 0 {
		return
	}
	if boundsTL.Y < 0 {
		boundsTL.Y = 0
	}
	if boundsTL.X < 0 {
		boundsTL.X = 0
	}
	if boundsBR.Y >= int(fb.Height) {
		boundsBR.Y = int(fb.Height - 1)
	}
	if boundsBR.X >= int(fb.Width) {
		boundsBR.X = int(fb.Width - 1)
	}
	// Where to start our scanning
	pstart := Vec2i{boundsTL.X, boundsTL.Y}
	// if parea < 0 {
	// 	v1, v2 = v2, v1
	// 	v1f, v2f = v2f, v1f
	// 	parea = EdgeFunctioni(v0, v1, v2)
	// }
	invarea := 1 / float32(parea)
	w0_y := EdgeFunctioni(v1, v2, pstart)
	w1_y := EdgeFunctioni(v2, v0, pstart)
	w2_y := EdgeFunctioni(v0, v1, pstart)
	w0_xi, w0_yi := EdgeIncrementi(v1, v2)
	w1_xi, w1_yi := EdgeIncrementi(v2, v0)
	w2_xi, w2_yi := EdgeIncrementi(v0, v1)

	for y := uint(boundsTL.Y); y <= uint(boundsBR.Y); y++ {
		w0 := w0_y
		w1 := w1_y
		w2 := w2_y
		for x := uint(boundsTL.X); x <= uint(boundsBR.X); x++ {
			if (w0 | w1 | w2) >= 0 {
				w0a := float32(w0) * invarea
				w1a := float32(w1) * invarea
				w2a := float32(w2) * invarea
				pz := uint16(w0a*v0v.Pos.Z + w1a*v1v.Pos.Z + w2a*v2v.Pos.Z)
				if pz < fb.ZBuffer[x+y*fb.Width] {
					fb.ZBuffer[x+y*fb.Width] = pz
					// if math.IsNaN(v0v.Tex.X) || math.IsNaN(v1v.Tex.X) || math.IsNaN
					col := texture.GetUv(
						(w0a*v0v.Tex.X + w1a*v1v.Tex.X + w2a*v2v.Tex.X),
						(w0a*v0v.Tex.Y + w1a*v1v.Tex.Y + w2a*v2v.Tex.Y),
					)
					r, g, b := Uint2Col(col)
					fb.Set(x, y, Col2Uint(byte(float32(r)*intensity), byte(float32(g)*intensity), byte(float32(b)*intensity))) //uint(texture.Bounds().Dx())
				}
			}
			w0 += w0_xi
			w1 += w1_xi
			w2 += w2_xi
		}
		w0_y += w0_yi
		w1_y += w1_yi
		w2_y += w2_yi
	}
}