graphics.go

/**
 *Copyright (c) 2018 Stephen Merrony
 *
 *This software is released under the MIT License.
 *https://opensource.org/licenses/MIT
 */

// graphics drawing primitives

package main

import (
	"image"
	"image/color"

	"golang.org/x/image/font"
	"golang.org/x/image/font/basicfont"
	"golang.org/x/image/math/fixed"
)

func drawPhysLabel(rgba *image.RGBA, x, y int, lab string, col color.Color) {
	point := fixed.Point26_6{
		X: fixed.Int26_6(x * 64),
		Y: fixed.Int26_6(y * 64)}
	d := &font.Drawer{
		Dst:  rgba,
		Src:  image.NewUniform(col),
		Face: basicfont.Face7x13,
		Dot:  point,
	}
	d.DrawString(lab)
}

// drawPhysLine draws a straight line using Bresenham's algorithm on an image.RGBA
// using physical coordinates (origin is top-left)
func drawPhysLine(rgba *image.RGBA, x0, y0, x1, y1 int, col color.Color) {
	dx := x1 - x0
	if dx < 0 {
		dx = -dx
	}
	dy := y1 - y0
	if dy < 0 {
		dy = -dy
	}
	var sx, sy int
	if x0 < x1 {
		sx = 1
	} else {
		sx = -1
	}
	if y0 < y1 {
		sy = 1
	} else {
		sy = -1
	}
	err := dx - dy
	for {
		rgba.Set(x0, y0, col)
		if x0 == x1 && y0 == y1 {
			break
		}
		e2 := 2 * err
		if e2 > -dy {
			err -= dy
			x0 += sx
		}
		if e2 < dx {
			err += dx
			y0 += sy
		}
	}
}