From 1d7a98b5c7537b4874645c56cd83ece9f78625f5 Mon Sep 17 00:00:00 2001 From: Carl Hetherington Date: Wed, 10 Jan 2018 00:25:47 +0000 Subject: [PATCH] Fix some incorrect alpha blending; may help with #1155. --- src/lib/image.cc | 28 +++++++++++++++++++++++----- 1 file changed, 23 insertions(+), 5 deletions(-) diff --git a/src/lib/image.cc b/src/lib/image.cc index b85451fb3..827ece5fd 100644 --- a/src/lib/image.cc +++ b/src/lib/image.cc @@ -439,7 +439,7 @@ Image::make_transparent () void Image::alpha_blend (shared_ptr other, Position position) { - /* We're blending RGBA images; first byte is blue, second byte is green, third byte blue, fourth byte alpha */ + /* 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); int const other_bpp = 4; @@ -464,6 +464,24 @@ Image::alpha_blend (shared_ptr other, Position position) { /* Going onto RGB24. First byte is red, second green, third blue */ int const this_bpp = 3; + for (int ty = start_ty, oy = start_oy; ty < size().height && oy < other->size().height; ++ty, ++oy) { + uint8_t* tp = data()[0] + ty * stride()[0] + start_tx * this_bpp; + 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[1] = op[1] * alpha + tp[1] * (1 - alpha); + tp[2] = op[2] * alpha + tp[2] * (1 - alpha); + + tp += this_bpp; + op += other_bpp; + } + } + break; + } + case AV_PIX_FMT_BGRA: + { + int const this_bpp = 4; for (int ty = start_ty, oy = start_oy; ty < size().height && oy < other->size().height; ++ty, ++oy) { uint8_t* tp = data()[0] + ty * stride()[0] + start_tx * this_bpp; uint8_t* op = other->data()[0] + oy * other->stride()[0]; @@ -472,6 +490,7 @@ Image::alpha_blend (shared_ptr other, Position position) tp[0] = op[2] * alpha + tp[0] * (1 - alpha); tp[1] = op[1] * alpha + tp[1] * (1 - alpha); tp[2] = op[0] * alpha + tp[2] * (1 - alpha); + tp[3] = op[3] * alpha + tp[3] * (1 - alpha); tp += this_bpp; op += other_bpp; @@ -479,7 +498,6 @@ Image::alpha_blend (shared_ptr other, Position position) } break; } - case AV_PIX_FMT_BGRA: case AV_PIX_FMT_RGBA: { int const this_bpp = 4; @@ -507,10 +525,10 @@ Image::alpha_blend (shared_ptr other, Position 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; - /* Blend high bytes; the RGBA in op appears to be BGRA */ - tp[1] = op[2] * alpha + tp[1] * (1 - alpha); + /* Blend high bytes */ + tp[1] = op[0] * alpha + tp[1] * (1 - alpha); tp[3] = op[1] * alpha + tp[3] * (1 - alpha); - tp[5] = op[0] * alpha + tp[5] * (1 - alpha); + tp[5] = op[2] * alpha + tp[5] * (1 - alpha); tp += this_bpp; op += other_bpp; -- 2.30.2