buffered: Do not delay commands if possible

Delaying commands causes memory allocations, which can be heavy
especially on browsers.

This avoids to use 'defer' for performance.

internal/buffered/command.go

@@ -19,40 +19,26 @@ import (
 )
 
 var (
-	delayedCommandsFlushable bool
+	needsToDelayCommands = true
 
 	// delayedCommands represents a queue for image operations that are ordered before the game starts
 	// (BeginFrame). Before the game starts, the package shareable doesn't determine the minimum/maximum texture
 	// sizes (#879).
-	//
-	// TODO: Flush the commands only when necessary (#921).
 	delayedCommands  []func()
 	delayedCommandsM sync.Mutex
 )
 
-func makeDelayedCommandFlushable() {
+func flushDelayedCommands() {
-	delayedCommandsM.Lock()
-	delayedCommandsFlushable = true
-	delayedCommandsM.Unlock()
-}
-
-func enqueueDelayedCommand(f func()) {
-	delayedCommandsM.Lock()
-	delayedCommands = append(delayedCommands, f)
-	delayedCommandsM.Unlock()
-}
-
-func flushDelayedCommands() bool {
 	delayedCommandsM.Lock()
 	defer delayedCommandsM.Unlock()
 
-	if !delayedCommandsFlushable {
+	if !needsToDelayCommands {
-		return false
+		return
 	}
 
 	for _, c := range delayedCommands {
 		c()
 	}
 	delayedCommands = delayedCommands[:0]
-	return true
+	needsToDelayCommands = false
 }

internal/buffered/image.go

@@ -30,77 +30,130 @@ func BeginFrame() error {
 	if err := shareable.BeginFrame(); err != nil {
 		return err
 	}
-	makeDelayedCommandFlushable()
+	flushDelayedCommands()
-
 	return nil
 }
 
 func EndFrame() error {
-	if !flushDelayedCommands() {
-		panic("buffered: the command queue must be available at EndFrame")
-	}
 	return shareable.EndFrame()
 }
 
 func NewImage(width, height int, volatile bool) *Image {
 	i := &Image{}
-	enqueueDelayedCommand(func() {
+	delayedCommandsM.Lock()
+	if needsToDelayCommands {
+		delayedCommands = append(delayedCommands, func() {
 			i.img = shareable.NewImage(width, height, volatile)
 		})
+		delayedCommandsM.Unlock()
+		return i
+	}
+	delayedCommandsM.Unlock()
+
+	i.img = shareable.NewImage(width, height, volatile)
 	return i
 }
 
 func NewScreenFramebufferImage(width, height int) *Image {
 	i := &Image{}
-	enqueueDelayedCommand(func() {
+	delayedCommandsM.Lock()
+	if needsToDelayCommands {
+		delayedCommands = append(delayedCommands, func() {
 			i.img = shareable.NewScreenFramebufferImage(width, height)
 		})
+		delayedCommandsM.Unlock()
+		return i
+	}
+	delayedCommandsM.Unlock()
+
+	i.img = shareable.NewScreenFramebufferImage(width, height)
 	return i
 }
 
 func (i *Image) MarkDisposed() {
-	enqueueDelayedCommand(func() {
+	delayedCommandsM.Lock()
+	if needsToDelayCommands {
+		delayedCommands = append(delayedCommands, func() {
 			i.img.MarkDisposed()
 		})
+	}
+	delayedCommandsM.Unlock()
 }
 
 func (i *Image) At(x, y int) (r, g, b, a byte) {
-	if !flushDelayedCommands() {
+	delayedCommandsM.Lock()
+	defer delayedCommandsM.Unlock()
+	if needsToDelayCommands {
 		panic("buffered: the command queue is not available yet at At")
 	}
 	return i.img.At(x, y)
 }
 
 func (i *Image) Dump(name string) error {
-	if !flushDelayedCommands() {
+	delayedCommandsM.Lock()
+	defer delayedCommandsM.Unlock()
+	if needsToDelayCommands {
 		panic("buffered: the command queue is not available yet at Dump")
 	}
 	return i.img.Dump(name)
 }
 
 func (i *Image) Fill(clr color.RGBA) {
-	enqueueDelayedCommand(func() {
+	delayedCommandsM.Lock()
+	if needsToDelayCommands {
+		delayedCommands = append(delayedCommands, func() {
 			i.img.Fill(clr)
 		})
+		delayedCommandsM.Unlock()
+		return
+	}
+	delayedCommandsM.Unlock()
+
+	i.img.Fill(clr)
 }
 
 func (i *Image) ClearFramebuffer() {
-	enqueueDelayedCommand(func() {
+	delayedCommandsM.Lock()
+	if needsToDelayCommands {
+		delayedCommands = append(delayedCommands, func() {
 			i.img.ClearFramebuffer()
 		})
+		delayedCommandsM.Unlock()
+		return
+	}
+	delayedCommandsM.Unlock()
+
+	i.img.ClearFramebuffer()
 }
 
 func (i *Image) ReplacePixels(pix []byte) {
-	enqueueDelayedCommand(func() {
+	delayedCommandsM.Lock()
+	if needsToDelayCommands {
+		delayedCommands = append(delayedCommands, func() {
 			i.img.ReplacePixels(pix)
 		})
+		delayedCommandsM.Unlock()
+		return
+	}
+	delayedCommandsM.Unlock()
+
+	i.img.ReplacePixels(pix)
 }
 
 func (i *Image) DrawTriangles(src *Image, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address) {
 	if i == src {
 		panic("buffered: Image.DrawTriangles: src must be different from the receiver")
 	}
-	enqueueDelayedCommand(func() {
+
+	delayedCommandsM.Lock()
+	if needsToDelayCommands {
+		delayedCommands = append(delayedCommands, func() {
 			i.img.DrawTriangles(src.img, vertices, indices, colorm, mode, filter, address)
 		})
+		delayedCommandsM.Unlock()
+		return
+	}
+	delayedCommandsM.Unlock()
+
+	i.img.DrawTriangles(src.img, vertices, indices, colorm, mode, filter, address)
 }