ebiten/examples/contextlost/main.go

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// Copyright 2018 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// +build js
// +build example jsgo
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package main
import (
"bytes"
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"fmt"
"image"
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_ "image/jpeg"
"log"
"math"
"syscall/js"
"time"
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"github.com/hajimehoshi/ebiten"
"github.com/hajimehoshi/ebiten/ebitenutil"
"github.com/hajimehoshi/ebiten/examples/resources/images"
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"github.com/hajimehoshi/ebiten/inpututil"
)
const (
screenWidth = 320
screenHeight = 240
)
var (
gophersImage *ebiten.Image
extraImages []*ebiten.Image
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)
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type Game struct {
count int
lost bool
}
func (g *Game) loseAndRestoreContext(context js.Value) {
if g.lost {
return
}
// Edge might not support the extension. See
// https://developer.mozilla.org/en-US/docs/Web/API/WEBGL_lose_context
ext := context.Call("getExtension", "WEBGL_lose_context")
if !ext.Truthy() {
fmt.Println("Fail to force context lost. Edge might not support the extension yet.")
return
}
ext.Call("loseContext")
fmt.Println("Lost the context!")
fmt.Println("The context is automatically restored after 3 seconds.")
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g.lost = true
// If and only if the context is lost by loseContext, you need to call restoreContext. Note that in usual
// case of context lost, you cannot call restoreContext but the context should be restored automatically.
//
// After the context is lost, update will not be called. Instead, fire the goroutine to restore the context.
go func() {
time.Sleep(3 * time.Second)
ext.Call("restoreContext")
fmt.Println("Restored the context!")
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g.lost = false
}()
}
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func (g *Game) Update(screen *ebiten.Image) error {
if inpututil.IsKeyJustPressed(ebiten.KeySpace) {
doc := js.Global().Get("document")
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canvas := doc.Call("getElementsByTagName", "canvas").Index(0)
context := canvas.Call("getContext", "webgl2")
if !context.Truthy() {
context = canvas.Call("getContext", "webgl")
if !context.Truthy() {
context = canvas.Call("getContext", "experimental-webgl")
}
}
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g.loseAndRestoreContext(context)
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return nil
}
if inpututil.IsKeyJustPressed(ebiten.KeyS) {
ebiten.SetClearingScreenSkipped(!ebiten.IsClearingScreenSkipped())
}
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g.count++
return nil
}
func (g *Game) Draw(screen *ebiten.Image) {
if g.lost {
// When the context is lost, skip rendering. Usually this logic should not be required, but when the
// context lost happens by the API explicitly, Draw can be called even after the data in GPU is
// disappered.
return
}
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w, h := gophersImage.Size()
op := &ebiten.DrawImageOptions{}
// For the details, see examples/rotate.
op.GeoM.Translate(-float64(w)/2, -float64(h)/2)
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op.GeoM.Rotate(float64(g.count%360) * 2 * math.Pi / 360)
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op.GeoM.Translate(screenWidth/2, screenHeight/2)
screen.DrawImage(gophersImage, op)
msg := `Press Space to force to lose/restore the GL context!
(Browser only)
Press S to switch clearing the screen
at the beginning of each frame.`
ebitenutil.DebugPrint(screen, msg)
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}
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func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
return screenWidth, screenHeight
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}
func main() {
// Decode image from a byte slice instead of a file so that
// this example works in any working directory.
// If you want to use a file, there are some options:
// 1) Use os.Open and pass the file to the image decoder.
// This is a very regular way, but doesn't work on browsers.
// 2) Use ebitenutil.OpenFile and pass the file to the image decoder.
// This works even on browsers.
// 3) Use ebitenutil.NewImageFromFile to create an ebiten.Image directly from a file.
// This also works on browsers.
img, _, err := image.Decode(bytes.NewReader(images.Gophers_jpg))
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if err != nil {
log.Fatal(err)
}
gophersImage, _ = ebiten.NewImageFromImage(img, ebiten.FilterDefault)
// Extend the shared backend GL texture on purpose.
for i := 0; i < 20; i++ {
eimg, _ := ebiten.NewImageFromImage(img, ebiten.FilterDefault)
extraImages = append(extraImages, eimg)
}
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ebiten.SetWindowSize(screenWidth*2, screenHeight*2)
ebiten.SetWindowTitle("Context Lost (Ebiten Demo)")
if err := ebiten.RunGame(&Game{}); err != nil {
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log.Fatal(err)
}
}