alpha patterns

internal/generator/v210.go

@@ -18,3 +18,20 @@ func V210LineSize(width int) int {
 func V210FrameSize(width, height int) int {
 	return V210LineSize(width) * height
 }
+
+// AlphaLineSize returns the byte stride of one packed 10-bit alpha row. Each
+// little-endian 32-bit word contains three alpha samples and two unused bits.
+func AlphaLineSize(width int) int {
+	return ((width + 2) / 3) * 4
+}
+
+// AlphaFrameSize returns the size of the alpha plane in a v210a frame.
+func AlphaFrameSize(width, height int) int {
+	return AlphaLineSize(width) * height
+}
+
+// V210AFrameSize returns the total size of a v210a payload: the complete v210
+// fill plane followed by the complete packed 10-bit alpha plane.
+func V210AFrameSize(width, height int) int {
+	return V210FrameSize(width, height) + AlphaFrameSize(width, height)
+}