internal/ui: bug fix: panic at ReadPixels before running

Closes #2820

internal/processtest/testdata/issue2820.go

@@ -0,0 +1,47 @@
+// Copyright 2023 The Ebitengine 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.
+
+//go:build ignore
+
+package main
+
+import (
+	"time"
+
+	"github.com/hajimehoshi/ebiten/v2"
+)
+
+func init() {
+	defer func() {
+		if e := recover(); e == nil {
+			panic("(*ebiten.Image).At before the main loop must panic but not (1)")
+		}
+	}()
+
+	done := make(chan struct{})
+	go func() {
+		select {
+		case <-done:
+			panic("(*ebiten.Image).At before the main loop must panic but not (2)")
+		case <-time.After(time.Second):
+			panic("(*ebiten.Image).At times out unexpectedly")
+		}
+	}()
+	img := ebiten.NewImage(1, 1)
+	img.At(0, 0)
+	close(done)
+}
+
+func main() {
+}

internal/ui/image.go

@@ -154,6 +154,10 @@ func (i *Image) WritePixels(pix []byte, region image.Rectangle) {
 }
 
 func (i *Image) ReadPixels(pixels []byte, region image.Rectangle) {
+	if !i.ui.isRunning() {
+		panic("ui: ReadPixels cannot be called before the game starts")
+	}
+
 	// Check the error existence and avoid unnecessary calls.
 	if i.ui.error() != nil {
 		return

internal/ui/input_js.go

@@ -200,7 +200,7 @@ func init() {
 }
 
 func (u *UserInterface) KeyName(key Key) string {
-	if !u.running {
+	if !u.isRunning() {
 		return ""
 	}
 

internal/ui/run_glfw_notsinglethread.go

@@ -26,8 +26,6 @@ import (
 )
 
 func (u *UserInterface) Run(game Game, options *RunOptions) error {
-	u.context = newContext(game)
-
 	u.mainThread = thread.NewOSThread()
 	u.renderThread = thread.NewOSThread()
 	graphicscommand.SetRenderThread(u.renderThread)
@@ -38,6 +36,8 @@ func (u *UserInterface) Run(game Game, options *RunOptions) error {
 	u.setRunning(true)
 	defer u.setRunning(false)
 
+	u.context = newContext(game)
+
 	if err := u.initOnMainThread(options); err != nil {
 		return err
 	}

internal/ui/run_glfw_singlethread.go

@@ -22,8 +22,6 @@ import (
 )
 
 func (u *UserInterface) Run(game Game, options *RunOptions) error {
-	u.context = newContext(game)
-
 	// Initialize the main thread first so the thread is available at u.run (#809).
 	u.mainThread = thread.NewNoopThread()
 	u.renderThread = thread.NewNoopThread()
@@ -32,6 +30,8 @@ func (u *UserInterface) Run(game Game, options *RunOptions) error {
 	u.setRunning(true)
 	defer u.setRunning(false)
 
+	u.context = newContext(game)
+
 	if err := u.initOnMainThread(options); err != nil {
 		return err
 	}

internal/ui/ui.go

@@ -74,6 +74,8 @@ type UserInterface struct {
 
 	isScreenClearedEveryFrame int32
 	graphicsLibrary           int32
+	running                   int32
+	terminated                int32
 
 	whiteImage *Image
 
@@ -176,3 +178,23 @@ func (u *UserInterface) setGraphicsLibrary(library GraphicsLibrary) {
 func (u *UserInterface) GraphicsLibrary() GraphicsLibrary {
 	return GraphicsLibrary(atomic.LoadInt32(&u.graphicsLibrary))
 }
+
+func (u *UserInterface) isRunning() bool {
+	return atomic.LoadInt32(&u.running) != 0 && !u.isTerminated()
+}
+
+func (u *UserInterface) setRunning(running bool) {
+	if running {
+		atomic.StoreInt32(&u.running, 1)
+	} else {
+		atomic.StoreInt32(&u.running, 0)
+	}
+}
+
+func (u *UserInterface) isTerminated() bool {
+	return atomic.LoadInt32(&u.terminated) != 0
+}
+
+func (u *UserInterface) setTerminated() {
+	atomic.StoreInt32(&u.terminated, 1)
+}

internal/ui/ui_glfw.go

@@ -24,7 +24,6 @@ import (
 	"os"
 	"runtime"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	"github.com/hajimehoshi/ebiten/v2/internal/file"
@@ -61,8 +60,6 @@ type userInterfaceImpl struct {
 	maxWindowWidthInDIP  int
 	maxWindowHeightInDIP int
 
-	running              uint32
-	terminated           uint32
 	runnableOnUnfocused  bool
 	fpsMode              FPSModeType
 	iconImages           []image.Image
@@ -286,26 +283,6 @@ func (u *UserInterface) Monitor() *Monitor {
 	return monitor
 }
 
-func (u *UserInterface) isRunning() bool {
-	return atomic.LoadUint32(&u.running) != 0 && !u.isTerminated()
-}
-
-func (u *UserInterface) isTerminated() bool {
-	return atomic.LoadUint32(&u.terminated) != 0
-}
-
-func (u *UserInterface) setRunning(running bool) {
-	if running {
-		atomic.StoreUint32(&u.running, 1)
-	} else {
-		atomic.StoreUint32(&u.running, 0)
-	}
-}
-
-func (u *UserInterface) setTerminated() {
-	atomic.StoreUint32(&u.terminated, 1)
-}
-
 // setWindowMonitor must be called on the main thread.
 func (u *UserInterface) setWindowMonitor(monitor *Monitor) error {
 	if microsoftgdk.IsXbox() {

internal/ui/ui_js.go

@@ -91,7 +91,6 @@ type userInterfaceImpl struct {
 	runnableOnUnfocused bool
 	fpsMode             FPSModeType
 	renderingScheduled  bool
-	running             bool
 	cursorMode          CursorMode
 	cursorPrevMode      CursorMode
 	captureCursorLater  bool
@@ -744,6 +743,9 @@ func (u *UserInterface) forceUpdateOnMinimumFPSMode() {
 }
 
 func (u *UserInterface) Run(game Game, options *RunOptions) error {
+	u.setRunning(true)
+	defer u.setRunning(false)
+
 	if !options.InitUnfocused && window.Truthy() {
 		// Do not focus the canvas when the current document is in an iframe.
 		// Otherwise, the parent page tries to focus the iframe on every loading, which is annoying (#1373).
@@ -752,7 +754,7 @@ func (u *UserInterface) Run(game Game, options *RunOptions) error {
 			canvas.Call("focus")
 		}
 	}
-	u.running = true
+
 	g, lib, err := newGraphicsDriver(&graphicsDriverCreatorImpl{
 		canvas: canvas,
 	}, options.GraphicsLibrary)

internal/ui/ui_mobile.go

@@ -269,8 +269,6 @@ func (u *UserInterface) run(game Game, mainloop bool, options *RunOptions) (err
 		}
 	}()
 
-	u.context = newContext(game)
-
 	var mgl gl.Context
 	if mainloop {
 		// When gomobile-build is used, GL functions must be called via
@@ -281,6 +279,11 @@ func (u *UserInterface) run(game Game, mainloop bool, options *RunOptions) (err
 		graphicscommand.SetRenderThread(u.renderThread)
 	}
 
+	u.setRunning(true)
+	defer u.setRunning(false)
+
+	u.context = newContext(game)
+
 	g, lib, err := newGraphicsDriver(&graphicsDriverCreatorImpl{
 		gomobileContext: mgl,
 	}, options.GraphicsLibrary)

internal/ui/ui_nintendosdk.go

@@ -84,7 +84,15 @@ func (u *UserInterface) init() error {
 }
 
 func (u *UserInterface) Run(game Game, options *RunOptions) error {
+	u.mainThread = thread.NewOSThread()
+	u.renderThread = thread.NewOSThread()
+	graphicscommand.SetRenderThread(u.renderThread)
+
+	u.setRunning(true)
+	defer u.setRunning(false)
+
 	u.context = newContext(game)
+
 	g, lib, err := newGraphicsDriver(&graphicsDriverCreatorImpl{}, options.GraphicsLibrary)
 	if err != nil {
 		return err
@@ -99,10 +107,6 @@ func (u *UserInterface) Run(game Game, options *RunOptions) error {
 
 	initializeProfiler()
 
-	u.mainThread = thread.NewOSThread()
-	u.renderThread = thread.NewOSThread()
-	graphicscommand.SetRenderThread(u.renderThread)
-
 	ctx, cancel := stdcontext.WithCancel(stdcontext.Background())
 	defer cancel()
 

internal/ui/ui_playstation5.go

@@ -64,6 +64,9 @@ func (u *UserInterface) init() error {
 }
 
 func (u *UserInterface) Run(game Game, options *RunOptions) error {
+	u.setRunning(true)
+	defer u.setRunning(false)
+
 	// TODO: Implement this.
 	return nil
 }