graphics: Remove imageM (global lock)

graphicscontext.go

@@ -74,8 +74,6 @@ func (c *graphicsContext) SetSize(screenWidth, screenHeight int, screenScale flo
 }
 
 func (c *graphicsContext) needsRestoring(context *opengl.Context) (bool, error) {
-	imageM.Lock()
-	defer imageM.Unlock()
 	// FlushCommands is required because c.offscreen.impl might not have an actual texture.
 	if err := graphics.FlushCommands(context); err != nil {
 		return false, err
@@ -122,9 +120,6 @@ func (c *graphicsContext) drawToDefaultRenderTarget(context *opengl.Context) err
 	if err := drawWithFittingScale(c.screen, c.offscreen2); err != nil {
 		return err
 	}
-	// TODO: imageM is necessary to call graphics functions. Move this to graphics package.
-	imageM.Lock()
-	defer imageM.Unlock()
 	if err := graphics.FlushCommands(context); err != nil {
 		return err
 	}
@@ -164,8 +159,6 @@ func (c *graphicsContext) UpdateAndDraw(context *opengl.Context, updateCount int
 }
 
 func (c *graphicsContext) restore(context *opengl.Context) error {
-	imageM.Lock()
-	defer imageM.Unlock()
 	if err := graphics.Initialize(context); err != nil {
 		return err
 	}

imageimpl.go

@@ -28,10 +28,6 @@ import (
 	"github.com/hajimehoshi/ebiten/internal/ui"
 )
 
-var (
-	imageM sync.Mutex
-)
-
 type imageImpl struct {
 	image    *graphics.Image
 	screen   bool
@@ -99,8 +95,8 @@ func (i *imageImpl) At(x, y int) color.Color {
 	if !loop.IsRunning() {
 		panic("ebiten: At can't be called when the GL context is not initialized (this panic happens as of version 1.4.0-alpha)")
 	}
-	imageM.Lock()
-	defer imageM.Unlock()
+	i.m.Lock()
+	defer i.m.Unlock()
 	if i.isDisposed() {
 		return color.Transparent
 	}