3dtrial/tinyrender3/render.go

package main

import (
	//"log"
	"math"
)

func Bresenham2(fb *Framebuffer, color uint, x0 int, y0 int, x1 int, y1 int) {
	dx := int(math.Abs(float64(x1 - x0)))
	sx := -1
	if x0 < x1 {
		sx = 1
	}
	dy := -int(math.Abs(float64(y1 - y0)))
	sy := -1
	if y0 < y1 {
		sy = 1
	}
	err := dx + dy

	for {
		fb.SetSafe(uint(x0), uint(y0), color)
		if x0 == x1 && y0 == y1 {
			break
		}
		e2 := 2 * err
		if e2 >= dy {
			if x0 == x1 {
				break
			}
			err += dy
			x0 += sx
		}
		if e2 <= dx {
			if y0 == y1 {
				break
			}
			err += dx
			y0 += sy
		}
	}
}

func line(fb *Framebuffer, color uint, v0 Vec2i, v1 Vec2i) {
	Bresenham2(fb, color, v0.X, v0.Y, v1.X, v1.Y)
}

/*func LineSweep(fb *Framebuffer, color uint, v0 Vec2i, v1 Vec2i, v2 Vec2i) {

}*/

func Triangle1(fb *Framebuffer, color uint, v0 Vec2i, v1 Vec2i, v2 Vec2i) {
	// The dude gets rid of "degenerate" triangles so... we do too?
	if v2.Y == v1.Y && v1.Y == v0.Y {
		return
	}
	// Very silly manual sorting by Y
	if v2.Y < v0.Y {
		v0, v2 = v2, v0
	}
	if v1.Y < v0.Y {
		v0, v1 = v1, v0
	}
	if v2.Y < v1.Y {
		v1, v2 = v2, v1
	}

	var v02step, v01step, v12step, xlong, xshort float32

	xlong = float32(v0.X)
	xshort = xlong

	// The first and last Y CAN'T be equal because sorting!!
	if v1.Y == v0.Y {
		xshort = float32(v1.X)
	}

	// We can check just for greater than because we sorted the vertices
	// Assume 02 is on the right(?)  and 01 on the left
	v02step = (float32(v2.X - v0.X)) / (float32(v2.Y-v0.Y) + 0.001) // long side always
	v01step = (float32(v1.X - v0.X)) / (float32(v1.Y-v0.Y) + 0.001) // first short side
	v12step = (float32(v2.X - v1.X)) / (float32(v2.Y-v1.Y) + 0.001) // second short side

	for y := v0.Y; y <= v2.Y; y++ {
		xleft := int(xshort)
		xright := int(xlong)
		if xleft > xright {
			xleft, xright = xright, xleft
		}
		if xleft < 0 || xright >= int(fb.Width) {
			continue
		}
		// Draw a horizontal line from left to right
		for x := xleft; x <= xright; x++ {
			fb.SetSafe(uint(x), uint(y), color)
		}
		xlong += v02step
		if y < v1.Y {
			xshort += v01step
		} else {
			xshort += v12step
		}
	}
}

// How does this work? Compare with your
// other barycentric function (in a different repo). In the original
// cpp code, they used an overloaded operator ^ to mean cross product
func Barycentric(v0, v1, v2, p Vec2i) Vec3f {
	// WARN: Just not doing this one
	u := Vec3f{}
	if math.Abs(float64(u.Z)) < 1 {
		return Vec3f{-1, 1, 1}
	}
	return Vec3f{1 - (u.X+u.Y)/u.Z, u.Y / u.Z, u.X / u.Z}
}

// 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 Triangle2(fb *Framebuffer, color uint, v0 Vec2i, v1 Vec2i, v2 Vec2i) {
	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}
	//log.Print(boundsTL, boundsBR)
	// v0f := v0.ToF()
	// v1f := v1.ToF()
	// v2f := v2.ToF()
	// parea := EdgeFunction(v0f, v1f, v2f)
	// invarea := 1 / 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)
	//dyi := int(fb.Width)
	//dy := boundsTL.X + dyi*boundsTL.Y

	for y := uint(boundsTL.Y); y <= uint(boundsBR.Y); y++ {
		w0 := w0_y
		w1 := w1_y
		w2 := w2_y
		//di := dy
		//done := false
		for x := uint(boundsTL.X); x <= uint(boundsBR.X); x++ {
			if (w0 | w1 | w2) >= 0 {
				//fb.Data[di] = color
				fb.Set(x, y, color)
				//done = true
				// w0a := w0 * invarea
				// w1a := w1 * invarea
				// w2a := w2 * invarea
				// fb.Set(x, y, Col2Uint(byte(255*w0a), byte(255*w1a), byte(255*w2a)))
			} /*else if done {
				break
			}*/
			//di += 1
			w0 += w0_xi
			w1 += w1_xi
			w2 += w2_xi
		}
		//dy += dyi
		w0_y += w0_yi
		w1_y += w1_yi
		w2_y += w2_yi
	}
}

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 := 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
	}
}