internal/ui: pass the canvas element directly instead of an ID

internal/graphicsdriver/opengl/context_js.go

@@ -110,7 +110,7 @@ func uint8ArrayToSlice(value js.Value, length int) []byte {
 
 type contextImpl struct {
 	gl            *gl
-	canvasID      string
+	canvas        js.Value
 	lastProgramID programID
 	webGLVersion  webGLVersion
 }
@@ -126,7 +126,7 @@ func (c *context) initGL() error {
 
 	// TODO: Define id?
 	if doc := js.Global().Get("document"); doc.Truthy() {
-		canvas := doc.Call("getElementById", c.canvasID)
+		canvas := c.canvas
 		attr := js.Global().Get("Object").New()
 		attr.Set("alpha", true)
 		attr.Set("premultipliedAlpha", true)

internal/graphicsdriver/opengl/graphics_js.go

@@ -14,6 +14,10 @@
 
 package opengl
 
-func (g *Graphics) SetCanvasID(id string) {
-	g.context.canvasID = id
+import (
+	"syscall/js"
+)
+
+func (g *Graphics) SetCanvas(canvas js.Value) {
+	g.context.canvas = canvas
 }

internal/ui/ui_js.go

@@ -15,7 +15,6 @@
 package ui
 
 import (
-	"fmt"
 	"syscall/js"
 	"time"
 
@@ -438,8 +437,6 @@ func init() {
 	document.Get("head").Call("appendChild", meta)
 
 	canvas = document.Call("createElement", "canvas")
-	now := time.Now().UnixNano()
-	canvas.Set("id", fmt.Sprintf("ebitengine-%d.%d", now/1e9, (now%1e9)/1e6))
 	canvas.Set("width", 16)
 	canvas.Set("height", 16)
 
@@ -620,8 +617,8 @@ func (u *userInterfaceImpl) Run(game Game) error {
 		return err
 	}
 	u.graphicsDriver = g
-	if g, ok := u.graphicsDriver.(interface{ SetCanvasID(string) }); ok {
-		g.SetCanvasID(canvas.Get("id").String())
+	if g, ok := u.graphicsDriver.(interface{ SetCanvas(js.Value) }); ok {
+		g.SetCanvas(canvas)
 	}
 	return <-u.loop(game)
 }