graphics: Bug fix: GL context is not available until graphics context is initialized

graphicscontext.go

@@ -16,9 +16,11 @@ package ebiten
 
 import (
 	"math"
+	"sync/atomic"
 
 	"github.com/hajimehoshi/ebiten/internal/graphics"
 	"github.com/hajimehoshi/ebiten/internal/graphics/opengl"
+	"github.com/hajimehoshi/ebiten/internal/ui"
 )
 
 func newGraphicsContext(f func(*Image) error) *graphicsContext {
@@ -33,7 +35,14 @@ type graphicsContext struct {
 	offscreen2  *Image // TODO: better name
 	screen      *Image
 	screenScale float64
-	initialized bool
+	initialized int32
+}
+
+func (c *graphicsContext) GLContext() *opengl.Context {
+	if atomic.LoadInt32(&c.initialized) == 0 {
+		return nil
+	}
+	return ui.GLContext()
 }
 
 func (c *graphicsContext) SetSize(screenWidth, screenHeight int, screenScale float64) error {
@@ -82,11 +91,11 @@ func (c *graphicsContext) needsRestoring(context *opengl.Context) (bool, error)
 }
 
 func (c *graphicsContext) initializeIfNeeded(context *opengl.Context) error {
-	if !c.initialized {
+	if atomic.LoadInt32(&c.initialized) == 0 {
 		if err := graphics.Reset(context); err != nil {
 			return err
 		}
-		c.initialized = true
+		atomic.StoreInt32(&c.initialized, 1)
 	}
 	r, err := c.needsRestoring(context)
 	if err != nil {

image.go

@@ -21,9 +21,20 @@ import (
 	"sync"
 
 	"github.com/hajimehoshi/ebiten/internal/graphics/opengl"
-	"github.com/hajimehoshi/ebiten/internal/ui"
 )
 
+func glContext() *opengl.Context {
+	// This is called from finalizers even when the context or the program is not set.
+	g, ok := theGraphicsContext.Load().(*graphicsContext)
+	if !ok {
+		return nil
+	}
+	if g == nil {
+		return nil
+	}
+	return g.GLContext()
+}
+
 type images struct {
 	images map[*imageImpl]struct{}
 	m      sync.Mutex
@@ -141,7 +152,7 @@ func (i *Image) Size() (width, height int) {
 //
 // This function is concurrent-safe.
 func (i *Image) Clear() error {
-	if err := theImagesForRestoring.flushPixelsIfNeeded(i, ui.GLContext()); err != nil {
+	if err := theImagesForRestoring.flushPixelsIfNeeded(i, glContext()); err != nil {
 		return err
 	}
 	return i.impl.Fill(color.Transparent)
@@ -151,7 +162,7 @@ func (i *Image) Clear() error {
 //
 // This function is concurrent-safe.
 func (i *Image) Fill(clr color.Color) error {
-	if err := theImagesForRestoring.flushPixelsIfNeeded(i, ui.GLContext()); err != nil {
+	if err := theImagesForRestoring.flushPixelsIfNeeded(i, glContext()); err != nil {
 		return err
 	}
 	return i.impl.Fill(clr)
@@ -174,7 +185,7 @@ func (i *Image) Fill(clr color.Color) error {
 //
 // This function is concurrent-safe.
 func (i *Image) DrawImage(image *Image, options *DrawImageOptions) error {
-	if err := theImagesForRestoring.flushPixelsIfNeeded(i, ui.GLContext()); err != nil {
+	if err := theImagesForRestoring.flushPixelsIfNeeded(i, glContext()); err != nil {
 		return err
 	}
 	return i.impl.DrawImage(image, options)
@@ -202,7 +213,7 @@ func (i *Image) ColorModel() color.Model {
 //
 // This function is concurrent-safe.
 func (i *Image) At(x, y int) color.Color {
-	return i.impl.At(x, y, ui.GLContext())
+	return i.impl.At(x, y, glContext())
 }
 
 // Dispose disposes the image data. After disposing, the image becomes invalid.
@@ -212,7 +223,7 @@ func (i *Image) At(x, y int) color.Color {
 //
 // This function is concurrent-safe.
 func (i *Image) Dispose() error {
-	if err := theImagesForRestoring.flushPixelsIfNeeded(i, ui.GLContext()); err != nil {
+	if err := theImagesForRestoring.flushPixelsIfNeeded(i, glContext()); err != nil {
 		return err
 	}
 	if i.impl.isDisposed() {
@@ -229,7 +240,7 @@ func (i *Image) Dispose() error {
 //
 // This function is concurrent-safe.
 func (i *Image) ReplacePixels(p []uint8) error {
-	if err := theImagesForRestoring.flushPixelsIfNeeded(i, ui.GLContext()); err != nil {
+	if err := theImagesForRestoring.flushPixelsIfNeeded(i, glContext()); err != nil {
 		return err
 	}
 	return i.impl.ReplacePixels(p)

run.go

@@ -57,6 +57,8 @@ func IsRunningSlowly() bool {
 	return atomic.LoadInt32(&isRunningSlowly) != 0
 }
 
+var theGraphicsContext atomic.Value
+
 // Run runs the game.
 // f is a function which is called at every frame.
 // The argument (*Image) is the render target that represents the screen.
@@ -73,6 +75,7 @@ func Run(f func(*Image) error, width, height int, scale float64, title string) e
 	ch := make(chan error)
 	go func() {
 		g := newGraphicsContext(f)
+		theGraphicsContext.Store(g)
 		if err := loop.Run(g, width, height, scale, title, FPS); err != nil {
 			ch <- err
 		}
@@ -93,6 +96,7 @@ func RunWithoutMainLoop(f func(*Image) error, width, height int, scale float64,
 	ch := make(chan error)
 	go func() {
 		g := newGraphicsContext(f)
+		theGraphicsContext.Store(g)
 		if err := loop.Run(g, width, height, scale, title, FPS); err != nil {
 			ch <- err
 		}