探索如何用Golang实现一个基础的画布功能

import (
    "image"
    "image/color"
)

type canvas struct {
    width, height int
    bg            color.Color
    img           *image.RGBA
}

func newCanvas(width, height int, bg color.Color) *canvas {
    return &canvas{
        width:  width,
        height: height,
        bg:     bg,
        img:    image.NewRGBA(image.Rect(0, 0, width, height)),
    }
}

func (c *canvas) line(x1, y1, x2, y2 int, color color.Color) {
    lineColor := &color
    drawLine(c.img, x1, y1, x2, y2, lineColor)
}

func drawLine(img *image.RGBA, x1, y1, x2, y2 int, color *color.Color) {
    dx := abs(x2 - x1)
    sx := 1
    if x1 > x2 {
        sx = -1
    }
    dy := abs(y2 - y1)
    sy := 1
    if y1 > y2 {
        sy = -1
    }

    err := dx - dy

    for {
        img.Set(x1, y1, *color)
        if x1 == x2 && y1 == y2 {
            break
        }
        e2 := 2 * err
        if e2 > -dy {
            err -= dy
            x1 += sx
        }
        if e2 < dx {
            err += dx
            y1 += sy
        }
    }
}

func (c *canvas) rectangle(x1, y1, x2, y2 int, color color.Color) {
    rectColor := &color
    drawRectangle(c.img, x1, y1, x2, y2, rectColor)
}

func drawRectangle(img *image.RGBA, x1, y1, x2, y2 int, color *color.Color) {
    drawLine(img, x1, y1, x2, y1, color)
    drawLine(img, x2, y1, x2, y2, color)
    drawLine(img, x2, y2, x1, y2, color)
    drawLine(img, x1, y2, x1, y1, color)
}

func (c *canvas) output(filename string) error {
    file, err := os.Create(filename)
    if err != nil {
        return err
    }
    defer file.Close()

    err = png.Encode(file, c.img)
    if err != nil {
        return err
    }

    return nil
}

func main() {
    c := newCanvas(200, 200, color.White)

    // 画一条红线
    c.line(0, 0, 200, 200, color.RGBA{255, 0, 0, 255})

    // 画一个蓝色矩形
    c.rectangle(50, 50, 150, 150, color.RGBA{0, 0, 255, 255})

    // 输出到文件
    c.output("canvas.png")
}