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LibWeb+LibGfx: Support alpha in CanvasRenderingContext2D

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This is implemented by these related changes:

  * The Skia alpha type 'Opaque' is selected for surfaces that were
    created with the intention of not having an alpha channel.
    Previously we were simply creating one with alpha.

  * Clearing now happens through Skia's `clear()` which always uses the
    source color's value for the result, instead of setting all values
    to 0.

  * CanvasRenderingContext2D selects a different clearing color based on
    the `alpha` context attribute's value.
This commit is contained in:
Jelle Raaijmakers 2025-04-28 16:12:30 +02:00
commit 35efd4d14b
Notes: github-actions[bot] 2025-04-29 11:52:28 +00:00
7 changed files with 68 additions and 12 deletions
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8
Libraries/LibGfx/PaintingSurface.cpp
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@ -30,7 +30,7 @@ struct PaintingSurface::Impl {
NonnullRefPtr<PaintingSurface> PaintingSurface::create_with_size(RefPtr<SkiaBackendContext> context, IntSize size, BitmapFormat color_type, AlphaType alpha_type)
{
auto sk_color_type = to_skia_color_type(color_type);
auto sk_alpha_type = alpha_type == AlphaType::Premultiplied ? kPremul_SkAlphaType : kUnpremul_SkAlphaType;
auto sk_alpha_type = to_skia_alpha_type(color_type, alpha_type);
auto image_info = SkImageInfo::Make(size.width(), size.height(), sk_color_type, sk_alpha_type, SkColorSpace::MakeSRGB());
if (!context) {
@ -50,7 +50,7 @@ NonnullRefPtr<PaintingSurface> PaintingSurface::create_with_size(RefPtr<SkiaBack
NonnullRefPtr<PaintingSurface> PaintingSurface::wrap_bitmap(Bitmap& bitmap)
{
auto color_type = to_skia_color_type(bitmap.format());
auto alpha_type = bitmap.alpha_type() == AlphaType::Premultiplied ? kPremul_SkAlphaType : kUnpremul_SkAlphaType;
auto alpha_type = to_skia_alpha_type(bitmap.format(), bitmap.alpha_type());
auto size = bitmap.size();
auto image_info = SkImageInfo::Make(bitmap.width(), bitmap.height(), color_type, alpha_type, SkColorSpace::MakeSRGB());
auto surface = SkSurfaces::WrapPixels(image_info, bitmap.begin(), bitmap.pitch());
@ -102,7 +102,7 @@ PaintingSurface::~PaintingSurface()
void PaintingSurface::read_into_bitmap(Bitmap& bitmap)
{
auto color_type = to_skia_color_type(bitmap.format());
auto alpha_type = bitmap.alpha_type() == AlphaType::Premultiplied ? kPremul_SkAlphaType : kUnpremul_SkAlphaType;
auto alpha_type = to_skia_alpha_type(bitmap.format(), bitmap.alpha_type());
auto image_info = SkImageInfo::Make(bitmap.width(), bitmap.height(), color_type, alpha_type, SkColorSpace::MakeSRGB());
SkPixmap const pixmap(image_info, bitmap.begin(), bitmap.pitch());
m_impl->surface->readPixels(pixmap, 0, 0);
@ -111,7 +111,7 @@ void PaintingSurface::read_into_bitmap(Bitmap& bitmap)
void PaintingSurface::write_from_bitmap(Bitmap const& bitmap)
{
auto color_type = to_skia_color_type(bitmap.format());
auto alpha_type = bitmap.alpha_type() == AlphaType::Premultiplied ? kPremul_SkAlphaType : kUnpremul_SkAlphaType;
auto alpha_type = to_skia_alpha_type(bitmap.format(), bitmap.alpha_type());
auto image_info = SkImageInfo::Make(bitmap.width(), bitmap.height(), color_type, alpha_type, SkColorSpace::MakeSRGB());
SkPixmap const pixmap(image_info, bitmap.begin(), bitmap.pitch());
m_impl->surface->writePixels(pixmap, 0, 0);