drawing lines and stuff in Go

drawLine in Go.go

package main

import "golang.org/x/tour/pic"
import "math"

func lemp(x1, y1, dx, dy, t float64) (tx, ty float64) {
	tx = x1 - t * dx
	ty = y1 - t * dy
	return
}

func drawLine(canvas [][]uint8, x1, y1, x2, y2 float64) {
	dx, dy := x1 - x2, y1 - y2
	length := math.Sqrt(dx * dx + dy * dy)
	dt := 1.0 / length
	var draw_X, draw_Y float64
	for t := 1.0; t >= 0; t -= dt {
		draw_X, draw_Y = lemp(x1, y1, dx, dy, t)
		drawDot(canvas, draw_X, draw_Y)
	} 
}
func drawDot(canvas [][]uint8, x1, y1 float64) {
	canvas[int(y1)][int(x1)] += 50
}

func Pic(dx, dy int) [][]uint8 {
	rows := make([][]uint8, dy)

	// populate array [][]uint8
	for i := range rows {
		rows[i] = make([]uint8, dx)
	}

	rowslen := len(rows)
	colslen := len(rows[0])
	for i:= 10; i < rowslen; i += 5 {
		drawLine(rows,float64(i),float64(colslen - 10),20,0)
		drawLine(rows,float64(rowslen - 10), float64(i),20,0)
	}
	
	return rows
}

func main() {
	pic.Show(Pic)
}