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Core Concepts

Graphics deals with images, which are, in their simplest form, nothing more than two-dimensional arrays of pixels, containing color information for each pixel:


At the core, there are two main interfaces: image.Image and image/draw.Image. One serves as a readable image source, the other is used for drawing:
// image.Image
type Image interface {
ColorModel() color.Model
Bounds() Rectangle
At(x, y int) color.Color
// draw.Image is an image.Image with a Set method to change a single pixel.
type Image interface {
Set(x, y int, c color.Color)



Example: Creating a Circular Mask

This example has been taken from The Go image/draw package | The Go Blog​
type circle struct {
p image.Point
r int
func (c *circle) ColorModel() color.Model {
return color.AlphaModel
func (c *circle) Bounds() image.Rectangle {
return image.Rect(c.p.X-c.r, c.p.Y-c.r, c.p.X+c.r, c.p.Y+c.r)
func (c *circle) At(x, y int) color.Color {
xx, yy, rr := float64(x-c.p.X)+0.5, float64(y-c.p.Y)+0.5, float64(c.r)
if xx*xx+yy*yy < rr*rr {
return color.Alpha{255}
return color.Alpha{0}