A rendering engine library for Go supporting both SDL2 and WebAssembly (HTML Canvas) targets.
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package canvas
import (
// Engine implements a rendering engine targeting an HTML canvas for
// WebAssembly targets.
type Engine struct {
canvas Canvas
startTime time.Time
width int
height int
ticks uint32
// Private fields.
events *events.State
running bool
// Event channel. WASM subscribes to events asynchronously using the
// JavaScript APIs, whereas SDL2 polls the event queue which orders them
// all up for processing. This channel will order and queue the events.
queue chan Event
// New creates the Canvas Engine.
func New(canvasID string) (*Engine, error) {
canvas := GetCanvas(canvasID)
engine := &Engine{
canvas: canvas,
startTime: time.Now(),
events: events.New(),
width: canvas.ClientW(),
height: canvas.ClientH(),
queue: make(chan Event, 1024),
return engine, nil
// WindowSize returns the size of the canvas window.
func (e *Engine) WindowSize() (w, h int) {
return e.canvas.ClientW(), e.canvas.ClientH()
// GetTicks returns the number of milliseconds since the engine started.
func (e *Engine) GetTicks() uint32 {
ms := time.Since(e.startTime) * time.Millisecond
return uint32(ms)
func (e *Engine) Setup() error {
return nil
func (e *Engine) Present() error {
return nil
// Texture can hold on to cached image textures.
type Texture struct {
data string // data:image/png URI
image js.Value // DOM image element
width int
height int
// Size returns the dimensions of the texture.
func (t *Texture) Size() render.Rect {
return render.NewRect(int32(t.width), int32(t.height))
// NewBitmap initializes a texture from a bitmap image. The image is stored
// in HTML5 Session Storage.
func (e *Engine) NewBitmap(filename string) (render.Texturer, error) {
if data, ok := wasm.GetSession(filename); ok {
img := js.Global().Get("document").Call("createElement", "img")
img.Set("src", data)
return &Texture{
data: data,
image: img,
width: 60, // TODO
height: 60,
}, nil
return nil, errors.New("no bitmap data stored for " + filename)
var TODO int
// Copy a texturer bitmap onto the canvas.
func (e *Engine) Copy(t render.Texturer, src, dist render.Rect) {
tex := t.(*Texture)
// image := js.Global().Get("document").Call("createElement", "img")
// image.Set("src", tex.data)
// log.Info("drawing image just this once")
e.canvas.ctx2d.Call("drawImage", tex.image, dist.X, dist.Y)
// TODO++
// if TODO > 200 {
// log.Info("I exited at engine.Copy for canvas engine")
// os.Exit(0)
// }
// Delay for a moment.
func (e *Engine) Delay(delay uint32) {
time.Sleep(time.Duration(delay) * time.Millisecond)
// Teardown tasks.
func (e *Engine) Teardown() {}
func (e *Engine) Loop() error {
return nil