internal/debug: bug fix: add SwitchLogger to dump logs for each frame correctly

Closes #2731

internal/debug/debug.go

@@ -0,0 +1,20 @@
+// 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.
+
+package debug
+
+type Logger interface {
+	Logf(format string, args ...any)
+	Flush()
+}

internal/debug/debug_ebitenginedebug.go

@@ -18,10 +18,58 @@ package debug
 
 import (
 	"fmt"
+	"sync"
 )
 
 const IsDebug = true
 
+var theLogger = &logger{}
+
+var flushM sync.Mutex
+
+// Logf calls the current global logger's Logf.
+// Logf buffers the arguments and doesn't dump the log immediately.
+// You can dump logs by calling SwitchLogger and Flush.
+//
+// Logf is not concurrent safe.
 func Logf(format string, args ...any) {
-	fmt.Printf(format, args...)
+	theLogger.Logf(format, args...)
+}
+
+// SwitchLogger sets a new logger as the current logger and returns the original global logger.
+// The new global logger and the returned logger have separate statuses, so you can use them for different goroutines.
+//
+// SwitchLogger and a returned Logger are not concurrent safe.
+func SwitchLogger() Logger {
+	current := theLogger
+	theLogger = &logger{}
+	return current
+}
+
+type logger struct {
+	items []logItem
+}
+
+type logItem struct {
+	format string
+	args   []any
+}
+
+func (l *logger) Logf(format string, args ...any) {
+	l.items = append(l.items, logItem{
+		format: format,
+		args:   args,
+	})
+}
+
+func (l *logger) Flush() {
+	// Flushing is protected by a mutex not to mix another logger's logs.
+	flushM.Lock()
+	defer flushM.Unlock()
+
+	for i, item := range l.items {
+		fmt.Printf(item.format, item.args...)
+		l.items[i] = logItem{}
+	}
+	l.items = l.items[:0]
 }

internal/debug/debug_notebitenginedebug.go

@@ -20,3 +20,15 @@ const IsDebug = false
 
 func Logf(format string, args ...any) {
 }
+
+func SwitchLogger() Logger {
+	return dummyLogger{}
+}
+
+type dummyLogger struct{}
+
+func (dummyLogger) Logf(format string, args ...any) {
+}
+
+func (dummyLogger) Flush() {
+}

internal/graphicscommand/command.go

@@ -197,9 +197,13 @@ func (q *commandQueue) Flush(graphicsDriver graphicsdriver.Graphics, endFrame bo
 		}
 	}
 
+	logger := debug.SwitchLogger()
+
 	var flushErr error
 	runOnRenderThread(func() {
-		if err := q.flush(graphicsDriver, endFrame); err != nil {
+		defer logger.Flush()
+
+		if err := q.flush(graphicsDriver, endFrame, logger); err != nil {
 			if sync {
 				return
 			}
@@ -220,7 +224,7 @@ func (q *commandQueue) Flush(graphicsDriver graphicsdriver.Graphics, endFrame bo
 }
 
 // flush must be called the main thread.
-func (q *commandQueue) flush(graphicsDriver graphicsdriver.Graphics, endFrame bool) (err error) {
+func (q *commandQueue) flush(graphicsDriver graphicsdriver.Graphics, endFrame bool, logger debug.Logger) (err error) {
 	// If endFrame is true, Begin/End should be called to ensure the framebuffer is swapped.
 	if len(q.commands) == 0 && !endFrame {
 		return nil
@@ -228,7 +232,7 @@ func (q *commandQueue) flush(graphicsDriver graphicsdriver.Graphics, endFrame bo
 
 	es := q.indices
 	vs := q.vertices
-	debug.Logf("Graphics commands:\n")
+	logger.Logf("Graphics commands:\n")
 
 	if err := graphicsDriver.Begin(); err != nil {
 		return err
@@ -287,7 +291,7 @@ func (q *commandQueue) flush(graphicsDriver graphicsdriver.Graphics, endFrame bo
 			if err := c.Exec(graphicsDriver, indexOffset); err != nil {
 				return err
 			}
-			debug.Logf("  %s\n", c)
+			logger.Logf("  %s\n", c)
 			// TODO: indexOffset should be reset if the command type is different
 			// from the previous one. This fix is needed when another drawing command is
 			// introduced than drawTrianglesCommand.