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LibGfx: add support for interlaced GIFs

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Peter Nelson 2020-08-29 16:05:24 +01:00 • committed by Andreas Kling
parent 1341025da7
commit 786872e4c9
1 changed files with 21 additions and 1 deletions
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22
Libraries/LibGfx/GIFLoader.cpp
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@ -42,12 +42,17 @@ struct RGB {
u8 b;
};
// Row strides and offsets for each interlace pass.
static const int INTERLACE_ROW_STRIDES[] = { 8, 8, 4, 2 };
static const int INTERLACE_ROW_OFFSETS[] = { 0, 4, 2, 1 };
struct ImageDescriptor {
u16 x { 0 };
u16 y { 0 };
u16 width { 0 };
u16 height { 0 };
bool use_global_color_map { true };
bool interlaced { false };
RGB color_map[256];
u8 lzw_min_code_size { 0 };
Vector<u8> lzw_encoded_bytes;
@ -309,6 +314,8 @@ static bool decode_frames_up_to_index(GIFLoadingContext& context, size_t frame_i
}
int pixel_index = 0;
int row = 0;
int interlace_pass = 0;
while (true) {
Optional<u16> code = decoder.next_code();
if (!code.has_value()) {
@ -329,7 +336,7 @@ static bool decode_frames_up_to_index(GIFLoadingContext& context, size_t frame_i
auto rgb = color_map[color];
int x = pixel_index % image.width + image.x;
int y = pixel_index / image.width + image.y;
int y = row + image.y;
Color c = Color(rgb.r, rgb.g, rgb.b);
@ -342,6 +349,18 @@ static bool decode_frames_up_to_index(GIFLoadingContext& context, size_t frame_i
}
++pixel_index;
if (pixel_index % image.width == 0) {
if (image.interlaced) {
if (row + INTERLACE_ROW_STRIDES[interlace_pass] >= image.height) {
++interlace_pass;
row = INTERLACE_ROW_OFFSETS[interlace_pass];
} else {
row += INTERLACE_ROW_STRIDES[interlace_pass];
}
} else {
++row;
}
}
}
}
@ -506,6 +525,7 @@ static bool load_gif_frame_descriptors(GIFLoadingContext& context)
return false;
image.use_global_color_map = !(packed_fields & 0x80);
image.interlaced = (packed_fields & 0x40) != 0;
if (!image.use_global_color_map) {
size_t local_color_table_size = pow(2, (packed_fields & 7) + 1);