android: Bug fix: Black flicking (#226)

graphicscontext.go

@@ -75,7 +75,6 @@ func (c *graphicsContext) Update() error {
 	if IsRunningSlowly() {
 		return nil
 	}
-	// TODO: In WebGL, we don't need to clear the image here.
 	if err := c.defaultRenderTarget.Clear(); err != nil {
 		return err
 	}

internal/graphics/command.go

@@ -62,6 +62,8 @@ func (q *commandQueue) Flush(context *opengl.Context) error {
 			return err
 		}
 	}
+	// Call glFlush to prevent black flicking (especially on Android (#226)).
+	context.Flush()
 	q.commands = []command{}
 	return nil
 }
@@ -103,7 +105,6 @@ func (c *drawImageCommand) Exec(context *opengl.Context) error {
 	if n == 0 {
 		return nil
 	}
-
 	p := programContext{
 		state:            &theOpenGLState,
 		program:          theOpenGLState.programTexture,

internal/graphics/opengl/context_desktop.go

@@ -454,3 +454,10 @@ func (c *Context) DrawElements(mode Mode, len int, offsetInBytes int) {
 		return nil
 	})
 }
+
+func (c *Context) Flush() {
+	c.RunOnContextThread(func() error {
+		gl.Flush()
+		return nil
+	})
+}

internal/graphics/opengl/context_js.go

@@ -370,3 +370,8 @@ func (c *Context) DrawElements(mode Mode, len int, offsetInBytes int) {
 	gl := c.gl
 	gl.DrawElements(int(mode), len, gl.UNSIGNED_SHORT, offsetInBytes)
 }
+
+func (c *Context) Flush() {
+	gl := c.gl
+	gl.Flush()
+}

internal/graphics/opengl/context_mobile.go

@@ -373,3 +373,8 @@ func (c *Context) DrawElements(mode Mode, len int, offsetInBytes int) {
 	gl := c.gl
 	gl.DrawElements(mgl.Enum(mode), len, mgl.UNSIGNED_SHORT, offsetInBytes)
 }
+
+func (c *Context) Flush() {
+	gl := c.gl
+	gl.Flush()
+}

internal/ui/ui_mobile.go

@@ -44,8 +44,12 @@ loop:
 			return err
 		case <-worker.WorkAvailable():
 			worker.DoWork()
-		case <-chRenderEnd:
-			break loop
+		default:
+			select {
+			case <-chRenderEnd:
+				break loop
+			default:
+			}
 		}
 	}
 	return nil