alpha patterns

internal/generator/v210_test.go

@@ -2,6 +2,7 @@ package generator
 
 import (
 	"encoding/binary"
+	"fmt"
 	"testing"
 )
 
@@ -30,6 +31,46 @@ func TestV210Sizes(t *testing.T) {
 	}
 }
 
+func TestAlphaSizes(t *testing.T) {
+	tests := []struct {
+		width     int
+		height    int
+		lineSize  int
+		frameSize int
+		v210aSize int
+	}{
+		{
+			width: 1920, height: 1080,
+			lineSize: 2560, frameSize: 2_764_800, v210aSize: 8_294_400,
+		},
+		{
+			width: 1280, height: 720,
+			lineSize: 1708, frameSize: 1_229_760, v210aSize: 3_718_080,
+		},
+		{
+			width: 100, height: 2,
+			lineSize: 136, frameSize: 272, v210aSize: 1040,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(fmt.Sprintf("%dx%d", tc.width, tc.height), func(t *testing.T) {
+			if got := AlphaLineSize(tc.width); got != tc.lineSize {
+				t.Errorf("AlphaLineSize(%d) = %d, want %d", tc.width, got, tc.lineSize)
+			}
+			if got := AlphaFrameSize(tc.width, tc.height); got != tc.frameSize {
+				t.Errorf("AlphaFrameSize(%d, %d) = %d, want %d", tc.width, tc.height, got, tc.frameSize)
+			}
+			if got := V210AFrameSize(tc.width, tc.height); got != tc.v210aSize {
+				t.Errorf("V210AFrameSize(%d, %d) = %d, want %d", tc.width, tc.height, got, tc.v210aSize)
+			}
+			if got := V210AFrameSize(tc.width, tc.height) - AlphaFrameSize(tc.width, tc.height); got != V210FrameSize(tc.width, tc.height) {
+				t.Errorf("alpha plane starts at byte %d, want %d", got, V210FrameSize(tc.width, tc.height))
+			}
+		})
+	}
+}
+
 func sampleV210(buf []byte, width, x, y int) (yc, cb, cr uint32) {
 	offset := y*V210LineSize(width) + x/6*16
 	w0 := binary.LittleEndian.Uint32(buf[offset:])