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LibPDF: For low-bpp images, start scanlines on byte boundaries

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Required per spec, and we get slanted images without it. Fixes e.g.
page 1 of 0000749.pdf.
This commit is contained in:
Nico Weber 2023-12-06 18:53:19 -05:00 • committed by Sam Atkins
parent 06b9633da5
commit 832a065687
1 changed files with 13 additions and 3 deletions
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16
Userland/Libraries/LibPDF/Renderer.cpp
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@ -831,12 +831,14 @@ enum UpsampleMode {
StoreValuesUnchanged,
UpsampleTo8Bit,
};
static Vector<u8> upsample_to_8_bit(ReadonlyBytes content, int bits_per_component, UpsampleMode mode)
static Vector<u8> upsample_to_8_bit(ReadonlyBytes content, int samples_per_line, int bits_per_component, UpsampleMode mode)
{
VERIFY(bits_per_component == 1 || bits_per_component == 2 || bits_per_component == 4);
Vector<u8> upsampled_storage;
upsampled_storage.ensure_capacity(content.size() * 8 / bits_per_component);
u8 const mask = (1 << bits_per_component) - 1;
int x = 0;
for (auto byte : content) {
for (int i = 0; i < 8; i += bits_per_component) {
auto value = (byte >> (8 - bits_per_component - i)) & mask;
@ -844,6 +846,13 @@ static Vector<u8> upsample_to_8_bit(ReadonlyBytes content, int bits_per_componen
upsampled_storage.append(value * (255 / mask));
else
upsampled_storage.append(value);
++x;
// "Byte boundaries are ignored, except that each row of sample data must begin on a byte boundary."
if (x == samples_per_line) {
x = 0;
break;
}
}
}
return upsampled_storage;
@ -900,10 +909,12 @@ PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> Renderer::load_image(NonnullRefPtr<Stream
}
auto content = image->bytes();
int const n_components = color_space->number_of_components();
Vector<u8> upsampled_storage;
if (bits_per_component < 8) {
UpsampleMode mode = color_space->family() == ColorSpaceFamily::Indexed ? UpsampleMode::StoreValuesUnchanged : UpsampleMode::UpsampleTo8Bit;
upsampled_storage = upsample_to_8_bit(content, bits_per_component, mode);
upsampled_storage = upsample_to_8_bit(content, width * n_components, bits_per_component, mode);
content = upsampled_storage;
bits_per_component = 8;
}
@ -934,7 +945,6 @@ PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> Renderer::load_image(NonnullRefPtr<Stream
auto bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, { width, height }));
int x = 0;
int y = 0;
int const n_components = color_space->number_of_components();
auto const bytes_per_component = bits_per_component / 8;
Vector<Value> component_values;
component_values.resize(n_components);