Fix yet more pixel order confusions.

3 files changed, 17 insertions, 15 deletions

diff --git a/src/lib/image.cc b/src/lib/image.cc
index 827ece5fd..cb03e1a73 100644
--- a/src/lib/image.cc
+++ b/src/lib/image.cc
@@ -429,7 +429,7 @@ Image::make_black ()
 void
 Image::make_transparent ()
 {
-	if (_pixel_format != AV_PIX_FMT_RGBA) {
+	if (_pixel_format != AV_PIX_FMT_BGRA) {
 		throw PixelFormatError ("make_transparent()", _pixel_format);
 	}
 
@@ -439,8 +439,8 @@ Image::make_transparent ()
 void
 Image::alpha_blend (shared_ptr<const Image> other, Position<int> position)
 {
-	/* We're blending RGBA images; first byte is red, second byte is green, third byte blue, fourth byte alpha */
-	DCPOMATIC_ASSERT (other->pixel_format() == AV_PIX_FMT_RGBA);
+	/* We're blending BGRA images; first byte is blue, second byte is green, third byte red, fourth byte alpha */
+	DCPOMATIC_ASSERT (other->pixel_format() == AV_PIX_FMT_BGRA);
 	int const other_bpp = 4;
 
 	int start_tx = position.x;
@@ -469,9 +469,9 @@ Image::alpha_blend (shared_ptr<const Image> other, Position<int> position)
 			uint8_t* op = other->data()[0] + oy * other->stride()[0];
 			for (int tx = start_tx, ox = start_ox; tx < size().width && ox < other->size().width; ++tx, ++ox) {
 				float const alpha = float (op[3]) / 255;
-				tp[0] = op[0] * alpha + tp[0] * (1 - alpha);
+				tp[0] = op[2] * alpha + tp[0] * (1 - alpha);
 				tp[1] = op[1] * alpha + tp[1] * (1 - alpha);
-				tp[2] = op[2] * alpha + tp[2] * (1 - alpha);
+				tp[2] = op[0] * alpha + tp[2] * (1 - alpha);
 
 				tp += this_bpp;
 				op += other_bpp;
@@ -487,9 +487,9 @@ Image::alpha_blend (shared_ptr<const Image> other, Position<int> position)
 			uint8_t* op = other->data()[0] + oy * other->stride()[0];
 			for (int tx = start_tx, ox = start_ox; tx < size().width && ox < other->size().width; ++tx, ++ox) {
 				float const alpha = float (op[3]) / 255;
-				tp[0] = op[2] * alpha + tp[0] * (1 - alpha);
+				tp[0] = op[0] * alpha + tp[0] * (1 - alpha);
 				tp[1] = op[1] * alpha + tp[1] * (1 - alpha);
-				tp[2] = op[0] * alpha + tp[2] * (1 - alpha);
+				tp[2] = op[2] * alpha + tp[2] * (1 - alpha);
 				tp[3] = op[3] * alpha + tp[3] * (1 - alpha);
 
 				tp += this_bpp;
@@ -506,9 +506,9 @@ Image::alpha_blend (shared_ptr<const Image> other, Position<int> position)
 			uint8_t* op = other->data()[0] + oy * other->stride()[0];
 			for (int tx = start_tx, ox = start_ox; tx < size().width && ox < other->size().width; ++tx, ++ox) {
 				float const alpha = float (op[3]) / 255;
-				tp[0] = op[0] * alpha + tp[0] * (1 - alpha);
+				tp[0] = op[2] * alpha + tp[0] * (1 - alpha);
 				tp[1] = op[1] * alpha + tp[1] * (1 - alpha);
-				tp[2] = op[2] * alpha + tp[2] * (1 - alpha);
+				tp[2] = op[0] * alpha + tp[2] * (1 - alpha);
 				tp[3] = op[3] * alpha + tp[3] * (1 - alpha);
 
 				tp += this_bpp;
@@ -526,9 +526,9 @@ Image::alpha_blend (shared_ptr<const Image> other, Position<int> position)
 			for (int tx = start_tx, ox = start_ox; tx < size().width && ox < other->size().width; ++tx, ++ox) {
 				float const alpha = float (op[3]) / 255;
 				/* Blend high bytes */
-				tp[1] = op[0] * alpha + tp[1] * (1 - alpha);
+				tp[1] = op[2] * alpha + tp[1] * (1 - alpha);
 				tp[3] = op[1] * alpha + tp[3] * (1 - alpha);
-				tp[5] = op[2] * alpha + tp[5] * (1 - alpha);
+				tp[5] = op[0] * alpha + tp[5] * (1 - alpha);
 
 				tp += this_bpp;
 				op += other_bpp;
diff --git a/src/lib/render_subtitles.cc b/src/lib/render_subtitles.cc
index 9c4617ac3..56343cd50 100644
--- a/src/lib/render_subtitles.cc
+++ b/src/lib/render_subtitles.cc
@@ -123,7 +123,8 @@ render_line (list<SubtitleString> subtitles, list<shared_ptr<Font> > fonts, dcp:
 	/* ...and add a bit more for luck */
 	height += target.height / 11;
 
-	shared_ptr<Image> image (new Image (AV_PIX_FMT_RGBA, dcp::Size (target.width, height), false));
+	/* FFmpeg BGRA means first byte blue, second byte green, third byte red, fourth byte alpha */
+	shared_ptr<Image> image (new Image (AV_PIX_FMT_BGRA, dcp::Size (target.width, height), false));
 	image->make_black ();
 
 #ifdef DCPOMATIC_HAVE_FORMAT_STRIDE_FOR_WIDTH
@@ -132,6 +133,7 @@ render_line (list<SubtitleString> subtitles, list<shared_ptr<Font> > fonts, dcp:
 		Cairo::FORMAT_ARGB32,
 		image->size().width,
 		image->size().height,
+		/* Cairo ARGB32 means first byte blue, second byte green, third byte red, fourth byte alpha */
 		Cairo::ImageSurface::format_stride_for_width (Cairo::FORMAT_ARGB32, image->size().width)
 		);
 #else
diff --git a/test/image_test.cc b/test/image_test.cc
index 67daaa509..b0bbe2594 100644
--- a/test/image_test.cc
+++ b/test/image_test.cc
@@ -142,13 +142,13 @@ alpha_blend_test_one (AVPixelFormat format, string suffix)
 	shared_ptr<Image> raw = proxy->image();
 	shared_ptr<Image> background = raw->convert_pixel_format (dcp::YUV_TO_RGB_REC709, format, true, false);
 
-	shared_ptr<Image> overlay (new Image (AV_PIX_FMT_RGBA, raw->size(), true));
+	shared_ptr<Image> overlay (new Image (AV_PIX_FMT_BGRA, raw->size(), true));
 	overlay->make_transparent ();
 
 	for (int y = 0; y < 128; ++y) {
 		uint8_t* p = overlay->data()[0] + y * overlay->stride()[0];
 		for (int x = 0; x < 128; ++x) {
-			p[x * 4] = 255;
+			p[x * 4 + 2] = 255;
 			p[x * 4 + 3] = 255;
 		}
 	}
@@ -164,7 +164,7 @@ alpha_blend_test_one (AVPixelFormat format, string suffix)
 	for (int y = 256; y < 384; ++y) {
 		uint8_t* p = overlay->data()[0] + y * overlay->stride()[0];
 		for (int x = 0; x < 128; ++x) {
-			p[x * 4 + 2] = 255;
+			p[x * 4] = 255;
 			p[x * 4 + 3] = 255;
 		}
 	}