A rendering engine library for Go supporting both SDL2 and WebAssembly (HTML Canvas) targets.
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Render: Go Graphics Library

Render is a graphics rendering library for Go.

It supports SDL2 and HTML Canvas back-ends enabling its use for both desktop applications (Linux, Mac and Windows) and WebAssembly modules for running in the web browser.



package main

import (

func main() {
    mw := sdl.New("Hello World", 320, 240)

    if err := mw.Setup(); err != nil {

    // Text that we're gonna draw in the window.
    text := render.Text{
        Text:         "Hello, world!",
        Size:         24,
        Color:        render.SkyBlue,
        Shadow:       render.Blue,
        FontFilename: "DejaVuSans.ttf",

    // Compute the rendered size of the text.
    rect, _ := mw.ComputeTextRect(text)

    for {
        // Blank the window.

        // Poll for events (mouse clicks, keyboard keys, etc.)
        ev, err := mw.Poll()
        if err != nil {

        // Escape key closes the window.
        if ev.Escape {

        // Get the window size.
        w, h := mw.WindowSize()

        // Draw the text centered in the window.
        mw.DrawText(text, render.NewPoint(


See the examples/ directory for examples. More will come eventually, including some WebAssembly examples.

Project Status: Alpha

This module was written as part of my drawing-based maze game, code named Project: Doodle. It is currently in alpha status and its API may change and be cleaned up in the future.

There are a few API cleanup tasks on my to-do list for this project, but they will come later when I have a chance to update the Project: Doodle game accordingly:

  • I want to replace all int32 types with normal int -- int32 was used initially due to SDL2 but for the Go API I want to abstract this away.

Drawing Methods (Engine)

This package provides some basic primitive drawing methods which are implemented for SDL2 (desktops) and HTML Canvas (WebAssembly). See the render.Engine interface. The drawing methods supported are:

  • Clear(Color): blank the window and fill it with this color.
  • DrawPoint(Color, Point): draw a single pixel at a coordinate.
  • DrawLine(Color, A Point, B Point): draw a line between two points.
  • DrawRect(Color, Rect): draw a rectangle outline between two points.
  • DrawBox(Color, Rect): draw a filled rectangle between two points.
  • DrawText(Text, Point): draw text at a location.
  • StoreTexture(name string, image.Image): load a Go image.Image object into the engine as a "texture" that can be re-used and pasted on the canvas.
  • LoadTexture(filename string): load an image from disk into a texture.
  • Copy(Texturer, src Rect, dst Rect): copy a texture onto the canvas.

Drawing Types

This package defines a handful of types useful for drawing operations. See the godoc for full details.

Note: all int32 values are to become normal ints at some point in the future, pending refactor in my Project: Doodle game.

  • Color: an RGBA color holding uint8 values for each channel.
    • NewRGBA(red, green, blue, alpha uint8) to construct a new color.
  • Point: holds an X,Y pair of coordinates (int32, to become int at some point)
  • Rect: holds an X,Y and a W,H value (int32).
  • Text: holds text and configuration for rendering (color, stroke, shadow, size, etc.)

Shape Generator Functions

The render package includes a few convenience functions for drawing complex shapes.

The generator functions return a channel that yields all of the Points that should be drawn to complete the shape. Example:

var (
    A Point = render.NewPoint(10, 10)
    B Point = render.NewPoint(15, 20)

for pt := range render.IterLine(A, B) {
    engine.DrawPoint(render.Red, pt)
  • IterLine(A Point, B Point): draw a line from A to B.
  • IterRect(A Point, B Point): iterate all the points to draw a rectangle.
  • IterEllipse(A Point, B Point): draw an elipse fitting inside the rectangle bounded by points A and B.