3dtrial/tinyrender1/render.go

package main

import (
	"math"
)

// Draw a line using dumb
func LineDumb(fb *Framebuffer, color uint, x0 uint, y0 uint, x1 uint, y1 uint) {
	var t float32
	for t = 0; t < 1; t += 0.01 {
		// Very simple interpolation between x and y
		x := x0 + uint(float32(x1-x0)*t)
		y := y0 + uint(float32(y1-y0)*t)
		fb.Set(x, y, color)
	}
}

func LineDumb2(fb *Framebuffer, color uint, x0 uint, y0 uint, x1 uint, y1 uint) {
	for x := x0; x < x1; x++ {
		// For each pixel across, compute how far across we are and interpolate y
		t := float32(x-x0) / float32(x1-x0)
		y := uint(float32(y0)*(1-t) + float32(y1)*t)
		fb.Set(x, y, color)
	}
}

func LineDumb3(fb *Framebuffer, color uint, x0 int, y0 int, x1 int, y1 int) {
	steep := false
	// This one makes sure that going pixel by pixel will not make holes in the
	// other direction by always moving in the less steep direction.
	if math.Abs(float64(x0-x1)) < math.Abs(float64(y0-y1)) {
		x0, y0 = y0, x0
		x1, y1 = y1, x1
		steep = true
	}
	// Don't let lines be invisible, always go left to right
	if x0 > x1 { // need to be left to right
		x0, x1 = x1, x0
		y0, y1 = y1, y0 // Why are we swapping these? I guess because we're swapping the points...
	}
	// Same as dumb2, going across pixel by pixel. But "x" here might actually be y
	// because of the inverted direction
	for x := x0; x <= x1; x++ {
		t := float32(x-x0) / float32(x1-x0)
		y := uint(float32(y0)*(1-t) + float32(y1)*t)
		if steep {
			fb.Set(y, uint(x), color)
		} else {
			fb.Set(uint(x), y, color)
		}
	}
}

func LineDumb4(fb *Framebuffer, color uint, x0 int, y0 int, x1 int, y1 int) {
	steep := false
	// This one makes sure that going pixel by pixel will not make holes in the
	// other direction by always moving in the less steep direction.
	if math.Abs(float64(x1-x0)) < math.Abs(float64(y1-y0)) {
		x0, y0 = y0, x0
		x1, y1 = y1, x1
		steep = true
	}
	// Don't let lines be invisible, always go left to right
	if x0 > x1 { // need to be left to right
		x0, x1 = x1, x0
		y0, y1 = y1, y0 // Why are we swapping these? I guess because we're swapping the points...
	}
	dx := x1 - x0 // These MUST be POST calcs
	dy := y1 - y0
	// Delta error or something? Basically, as we move in one direction, we get farther
	// and farther off course if we never move in the OTHER direction. This is the amount
	// of that per x direction.
	derror := math.Abs(float64(dy) / float64(dx))
	y := uint(y0)
	var err float64
	// Same as dumb2, going across pixel by pixel. But "x" here might actually be y
	// because of the inverted direction
	for x := x0; x <= x1; x++ {
		if steep {
			fb.Set(y, uint(x), color)
		} else {
			fb.Set(uint(x), y, color)
		}
		err += derror
		if err > 0.5 {
			if y1 > y0 {
				y += 1
			} else {
				y = y - 1
			}
			err -= 1
		}
	}
}