3dtrial/tinyrender2/render.go

package main

import (
	"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
		}
		// 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
		}
	}
}