alpha perfomance fix

internal/generator/v210a.go

@@ -9,6 +9,7 @@ type V210AGenerator struct {
 	width     int
 	height    int
 	fillSize  int
+	fillBase  []byte
 	alphaBase []byte
 }
 
@@ -17,6 +18,7 @@ var _ FrameGenerator = (*V210AGenerator)(nil)
 func NewV210AGenerator(
 	fill FrameGenerator,
 	width, height uint,
+	fillDynamic bool,
 ) (*V210AGenerator, error) {
 	if fill == nil {
 		return nil, fmt.Errorf("v210a: fill generator is nil")
@@ -38,6 +40,12 @@ func NewV210AGenerator(
 	if err := fillAlphaPlane(g.alphaBase, g.width, g.height, alphaOpaque); err != nil {
 		return nil, fmt.Errorf("v210a: initialize alpha plane: %w", err)
 	}
+	if !fillDynamic {
+		g.fillBase = make([]byte, g.fillSize)
+		if err := fill.GenerateFrame(g.fillBase, 0); err != nil {
+			return nil, fmt.Errorf("v210a: initialize static fill: %w", err)
+		}
+	}
 	return g, nil
 }
 
@@ -47,8 +55,10 @@ func (g *V210AGenerator) GenerateFrame(dst []byte, frameIndex int) error {
 		return fmt.Errorf("v210a: destination is too small: got %d bytes, need %d", len(dst), need)
 	}
 
-	if err := g.fill.GenerateFrame(dst[:g.fillSize], frameIndex); err != nil {
-		return fmt.Errorf("v210a: generate fill frame %d: %w", frameIndex, err)
+	if g.fillBase != nil {
+		copy(dst[:g.fillSize], g.fillBase)
+	} else if err := g.fill.GenerateFrame(dst[:g.fillSize], frameIndex); err != nil {
+		return fmt.Errorf("v210a: generate dynamic fill frame %d: %w", frameIndex, err)
 	}
 	alpha := dst[g.fillSize:need]
 	copy(alpha, g.alphaBase)

internal/generator/v210a_test.go

@@ -32,7 +32,7 @@ func (g *fakeFrameGenerator) Close() error {
 func TestV210AGeneratorLayoutAndAlpha(t *testing.T) {
 	const width, height = 304, 200
 	fill := &fakeFrameGenerator{}
-	g, err := NewV210AGenerator(fill, width, height)
+	g, err := NewV210AGenerator(fill, width, height, true)
 	if err != nil {
 		t.Fatalf("NewV210AGenerator: %v", err)
 	}
@@ -58,7 +58,7 @@ func TestV210AGeneratorLayoutAndAlpha(t *testing.T) {
 
 func TestV210AGeneratorRestoresAlphaBase(t *testing.T) {
 	const width, height = 304, 200
-	g, err := NewV210AGenerator(&fakeFrameGenerator{}, width, height)
+	g, err := NewV210AGenerator(&fakeFrameGenerator{}, width, height, true)
 	if err != nil {
 		t.Fatalf("NewV210AGenerator: %v", err)
 	}
@@ -82,13 +82,68 @@ func TestV210AGeneratorRestoresAlphaBase(t *testing.T) {
 	}
 }
 
+func TestV210AGeneratorCachesStaticFill(t *testing.T) {
+	const width, height = 100, 20
+	fill := &fakeFrameGenerator{}
+	g, err := NewV210AGenerator(fill, width, height, false)
+	if err != nil {
+		t.Fatalf("NewV210AGenerator: %v", err)
+	}
+	if fill.calls != 1 {
+		t.Fatalf("fill calls after construction = %d, want 1", fill.calls)
+	}
+
+	dst := make([]byte, V210AFrameSize(width, height))
+	for _, frameIndex := range []int{7, 19} {
+		if err := g.GenerateFrame(dst, frameIndex); err != nil {
+			t.Fatalf("GenerateFrame(%d): %v", frameIndex, err)
+		}
+	}
+	if fill.calls != 1 {
+		t.Errorf("fill calls after two frames = %d, want 1", fill.calls)
+	}
+	for i, b := range dst[:V210FrameSize(width, height)] {
+		if b != 0 {
+			t.Fatalf("cached fill byte %d = %#x, want frame-zero value 0", i, b)
+		}
+	}
+}
+
+func TestV210AGeneratorRegeneratesDynamicFill(t *testing.T) {
+	const width, height = 100, 20
+	fill := &fakeFrameGenerator{}
+	g, err := NewV210AGenerator(fill, width, height, true)
+	if err != nil {
+		t.Fatalf("NewV210AGenerator: %v", err)
+	}
+	if fill.calls != 0 {
+		t.Fatalf("fill calls after construction = %d, want 0", fill.calls)
+	}
+
+	dst := make([]byte, V210AFrameSize(width, height))
+	for _, frameIndex := range []int{7, 19} {
+		if err := g.GenerateFrame(dst, frameIndex); err != nil {
+			t.Fatalf("GenerateFrame(%d): %v", frameIndex, err)
+		}
+	}
+	if fill.calls != 2 {
+		t.Errorf("fill calls after two frames = %d, want 2", fill.calls)
+	}
+	if got := dst[0]; got != 19 {
+		t.Errorf("dynamic fill byte = %#x, want frame-index value 0x13", got)
+	}
+}
+
 func TestV210AGeneratorErrors(t *testing.T) {
-	if _, err := NewV210AGenerator(nil, 1920, 1080); err == nil || !strings.Contains(err.Error(), "nil") {
+	if _, err := NewV210AGenerator(nil, 1920, 1080, false); err == nil || !strings.Contains(err.Error(), "nil") {
 		t.Fatalf("nil fill error = %v", err)
 	}
 
 	fillErr := errors.New("fill failed")
-	g, err := NewV210AGenerator(&fakeFrameGenerator{generateErr: fillErr}, 100, 20)
+	if _, err := NewV210AGenerator(&fakeFrameGenerator{generateErr: fillErr}, 100, 20, false); !errors.Is(err, fillErr) {
+		t.Fatalf("static fill initialization error = %v, want wrapped %v", err, fillErr)
+	}
+	g, err := NewV210AGenerator(&fakeFrameGenerator{generateErr: fillErr}, 100, 20, true)
 	if err != nil {
 		t.Fatalf("NewV210AGenerator: %v", err)
 	}
@@ -103,7 +158,7 @@ func TestV210AGeneratorErrors(t *testing.T) {
 func TestV210AGeneratorClosesFill(t *testing.T) {
 	closeErr := errors.New("close failed")
 	fill := &fakeFrameGenerator{closeErr: closeErr}
-	g, err := NewV210AGenerator(fill, 100, 20)
+	g, err := NewV210AGenerator(fill, 100, 20, false)
 	if err != nil {
 		t.Fatalf("NewV210AGenerator: %v", err)
 	}