LibWeb: Implement border radius corner clipping in GPU painter

It is implemented in the way identical to how it works in CPU painter:
1. SampleUnderCorners command saves pixels within corners into a
   texture.
2. BlitCornerClipping command uses the texture prepared earlier to
   restore pixels within corners.

Userland/Libraries/LibAccelGfx/GL.cpp

@@ -30,6 +30,8 @@ static GLenum to_gl_enum(BlendFactor factor)
         return GL_SRC_ALPHA;
     case BlendFactor::One:
         return GL_ONE;
+    case BlendFactor::Zero:
+        return GL_ZERO;
     case BlendFactor::OneMinusSrcAlpha:
         return GL_ONE_MINUS_SRC_ALPHA;
     }

Userland/Libraries/LibAccelGfx/GL.h

@@ -61,6 +61,7 @@ struct Framebuffer {
 void set_viewport(Gfx::IntRect);
 
 enum class BlendFactor {
+    Zero,
     One,
     OneMinusSrcAlpha,
     SrcAlpha,

Userland/Libraries/LibAccelGfx/Painter.cpp

@@ -168,6 +168,23 @@ void main() {
 }
 )";
 
+static void set_blending_mode(Painter::BlendingMode blending_mode)
+{
+    switch (blending_mode) {
+    case Painter::BlendingMode::AlphaAdd:
+        GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::One);
+        break;
+    case Painter::BlendingMode::AlphaOverride:
+        GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::Zero);
+        break;
+    case Painter::BlendingMode::AlphaPreserve:
+        GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::Zero, GL::BlendFactor::One);
+        break;
+    default:
+        VERIFY_NOT_REACHED();
+    }
+}
+
 HashMap<u32, GL::Texture> s_immutable_bitmap_texture_cache;
 
 NonnullOwnPtr<Painter> Painter::create(Context& context, NonnullRefPtr<Canvas> canvas)
@@ -249,12 +266,12 @@ void Painter::fill_rect(Gfx::FloatRect rect, Gfx::Color color)
     GL::delete_vertex_array(vao);
 }
 
-void Painter::fill_rect_with_rounded_corners(Gfx::IntRect const& rect, Color const& color, CornerRadius const& top_left_radius, CornerRadius const& top_right_radius, CornerRadius const& bottom_left_radius, CornerRadius const& bottom_right_radius)
+void Painter::fill_rect_with_rounded_corners(Gfx::IntRect const& rect, Color const& color, CornerRadius const& top_left_radius, CornerRadius const& top_right_radius, CornerRadius const& bottom_left_radius, CornerRadius const& bottom_right_radius, BlendingMode blending_mode)
 {
-    fill_rect_with_rounded_corners(rect.to_type<float>(), color, top_left_radius, top_right_radius, bottom_left_radius, bottom_right_radius);
+    fill_rect_with_rounded_corners(rect.to_type<float>(), color, top_left_radius, top_right_radius, bottom_left_radius, bottom_right_radius, blending_mode);
 }
 
-void Painter::fill_rect_with_rounded_corners(Gfx::FloatRect const& rect, Color const& color, CornerRadius const& top_left_radius, CornerRadius const& top_right_radius, CornerRadius const& bottom_left_radius, CornerRadius const& bottom_right_radius)
+void Painter::fill_rect_with_rounded_corners(Gfx::FloatRect const& rect, Color const& color, CornerRadius const& top_left_radius, CornerRadius const& top_right_radius, CornerRadius const& bottom_left_radius, CornerRadius const& bottom_right_radius, BlendingMode blending_mode)
 {
     bind_target_canvas();
 
@@ -291,7 +308,8 @@ void Painter::fill_rect_with_rounded_corners(Gfx::FloatRect const& rect, Color c
     auto bottom_right_corner_radius_uniform = m_rounded_rectangle_program.get_uniform_location("uBottomRightRadius");
     GL::set_uniform(bottom_right_corner_radius_uniform, bottom_right_radius.horizontal_radius, bottom_right_radius.vertical_radius);
 
-    GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::One);
+    set_blending_mode(blending_mode);
+
     GL::draw_arrays(GL::DrawPrimitive::TriangleFan, 4);
 
     GL::delete_buffer(vbo);
@@ -627,7 +645,13 @@ void Painter::blit_canvas(Gfx::FloatRect const& dst_rect, Canvas const& canvas,
     blit_scaled_texture(dst_rect, texture, { { 0, 0 }, canvas.size() }, Painter::ScalingMode::NearestNeighbor, opacity, move(affine_transform));
 }
 
-void Painter::blit_scaled_texture(Gfx::FloatRect const& dst_rect, GL::Texture const& texture, Gfx::FloatRect const& src_rect, ScalingMode scaling_mode, float opacity, Optional<Gfx::AffineTransform> affine_transform)
+void Painter::blit_canvas(Gfx::FloatRect const& dst_rect, Canvas const& canvas, Gfx::FloatRect const& src_rect, float opacity, Optional<Gfx::AffineTransform> affine_transform, BlendingMode blending_mode)
+{
+    auto texture = GL::Texture(canvas.framebuffer().texture);
+    blit_scaled_texture(dst_rect, texture, src_rect, Painter::ScalingMode::NearestNeighbor, opacity, move(affine_transform), blending_mode);
+}
+
+void Painter::blit_scaled_texture(Gfx::FloatRect const& dst_rect, GL::Texture const& texture, Gfx::FloatRect const& src_rect, ScalingMode scaling_mode, float opacity, Optional<Gfx::AffineTransform> affine_transform, BlendingMode blending_mode)
 {
     bind_target_canvas();
 
@@ -689,7 +713,7 @@ void Painter::blit_scaled_texture(Gfx::FloatRect const& dst_rect, GL::Texture co
     auto scaling_mode_gl = to_gl_scaling_mode(scaling_mode);
     GL::set_texture_scale_mode(scaling_mode_gl);
 
-    GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::One);
+    set_blending_mode(blending_mode);
 
     GL::draw_arrays(GL::DrawPrimitive::TriangleFan, 4);
 

Userland/Libraries/LibAccelGfx/Painter.h

@@ -34,6 +34,8 @@ public:
     Painter(Context&, NonnullRefPtr<Canvas>);
     ~Painter();
 
+    Canvas const& canvas() { return *m_target_canvas; }
+
     void clear(Gfx::Color);
 
     void save();
@@ -53,6 +55,12 @@ public:
         Bilinear,
     };
 
+    enum class BlendingMode {
+        AlphaAdd,
+        AlphaOverride,
+        AlphaPreserve,
+    };
+
     void draw_line(Gfx::IntPoint a, Gfx::IntPoint b, float thickness, Gfx::Color color);
     void draw_line(Gfx::FloatPoint a, Gfx::FloatPoint b, float thickness, Gfx::Color color);
 
@@ -76,11 +84,12 @@ public:
         float horizontal_radius;
         float vertical_radius;
     };
-    void fill_rect_with_rounded_corners(Gfx::IntRect const& rect, Color const& color, CornerRadius const& top_left_radius, CornerRadius const& top_right_radius, CornerRadius const& bottom_left_radius, CornerRadius const& bottom_right_radius);
-    void fill_rect_with_rounded_corners(Gfx::FloatRect const& rect, Color const& color, CornerRadius const& top_left_radius, CornerRadius const& top_right_radius, CornerRadius const& bottom_left_radius, CornerRadius const& bottom_right_radius);
+    void fill_rect_with_rounded_corners(Gfx::IntRect const& rect, Color const& color, CornerRadius const& top_left_radius, CornerRadius const& top_right_radius, CornerRadius const& bottom_left_radius, CornerRadius const& bottom_right_radius, BlendingMode = BlendingMode::AlphaAdd);
+    void fill_rect_with_rounded_corners(Gfx::FloatRect const& rect, Color const& color, CornerRadius const& top_left_radius, CornerRadius const& top_right_radius, CornerRadius const& bottom_left_radius, CornerRadius const& bottom_right_radius, BlendingMode = BlendingMode::AlphaAdd);
 
     void blit_canvas(Gfx::IntRect const& dst_rect, Canvas const&, float opacity = 1.0f, Optional<Gfx::AffineTransform> affine_transform = {});
     void blit_canvas(Gfx::FloatRect const& dst_rect, Canvas const&, float opacity = 1.0f, Optional<Gfx::AffineTransform> affine_transform = {});
+    void blit_canvas(Gfx::FloatRect const& dst_rect, Canvas const&, Gfx::FloatRect const& src_rect, float opacity = 1.0f, Optional<Gfx::AffineTransform> affine_transform = {}, BlendingMode = BlendingMode::AlphaAdd);
 
     enum class BlurDirection {
         Horizontal,
@@ -101,7 +110,7 @@ private:
     [[nodiscard]] State& state() { return m_state_stack.last(); }
     [[nodiscard]] State const& state() const { return m_state_stack.last(); }
 
-    void blit_scaled_texture(Gfx::FloatRect const& dst_rect, GL::Texture const&, Gfx::FloatRect const& src_rect, ScalingMode, float opacity = 1.0f, Optional<Gfx::AffineTransform> affine_transform = {});
+    void blit_scaled_texture(Gfx::FloatRect const& dst_rect, GL::Texture const&, Gfx::FloatRect const& src_rect, ScalingMode, float opacity = 1.0f, Optional<Gfx::AffineTransform> affine_transform = {}, BlendingMode = BlendingMode::AlphaAdd);
     void blit_blurred_texture(Gfx::FloatRect const& dst_rect, GL::Texture const&, Gfx::FloatRect const& src_rect, int radius, BlurDirection direction, ScalingMode = ScalingMode::NearestNeighbor);
     void bind_target_canvas();
 

Userland/Libraries/LibWeb/Painting/PaintingCommandExecutorGPU.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <LibAccelGfx/GlyphAtlas.h>
+#include <LibWeb/Painting/BorderRadiusCornerClipper.h>
 #include <LibWeb/Painting/PaintingCommandExecutorGPU.h>
 
 namespace Web::Painting {
@@ -290,15 +291,77 @@ CommandResult PaintingCommandExecutorGPU::draw_triangle_wave(Gfx::IntPoint const
     return CommandResult::Continue;
 }
 
-CommandResult PaintingCommandExecutorGPU::sample_under_corners(u32, CornerRadii const&, Gfx::IntRect const&, CornerClip)
+CommandResult PaintingCommandExecutorGPU::sample_under_corners(u32 id, CornerRadii const& corner_radii, Gfx::IntRect const& border_rect, CornerClip)
 {
-    // FIXME
+    m_corner_clippers.resize(id + 1);
+    m_corner_clippers[id] = make<BorderRadiusCornerClipper>();
+    auto& corner_clipper = *m_corner_clippers[id];
+
+    auto const& top_left = corner_radii.top_left;
+    auto const& top_right = corner_radii.top_right;
+    auto const& bottom_right = corner_radii.bottom_right;
+    auto const& bottom_left = corner_radii.bottom_left;
+
+    auto sampling_config = calculate_border_radius_sampling_config(corner_radii, border_rect);
+    auto const& page_locations = sampling_config.page_locations;
+    auto const& bitmap_locations = sampling_config.bitmap_locations;
+
+    auto top_left_corner_size = Gfx::IntSize { top_left.horizontal_radius, top_left.vertical_radius };
+    auto top_right_corner_size = Gfx::IntSize { top_right.horizontal_radius, top_right.vertical_radius };
+    auto bottom_right_corner_size = Gfx::IntSize { bottom_right.horizontal_radius, bottom_right.vertical_radius };
+    auto bottom_left_corner_size = Gfx::IntSize { bottom_left.horizontal_radius, bottom_left.vertical_radius };
+
+    corner_clipper.page_top_left_rect = { page_locations.top_left, top_left_corner_size };
+    corner_clipper.page_top_right_rect = { page_locations.top_right, top_right_corner_size };
+    corner_clipper.page_bottom_right_rect = { page_locations.bottom_right, bottom_right_corner_size };
+    corner_clipper.page_bottom_left_rect = { page_locations.bottom_left, bottom_left_corner_size };
+
+    corner_clipper.sample_canvas_top_left_rect = { bitmap_locations.top_left, top_left_corner_size };
+    corner_clipper.sample_canvas_top_right_rect = { bitmap_locations.top_right, top_right_corner_size };
+    corner_clipper.sample_canvas_bottom_right_rect = { bitmap_locations.bottom_right, bottom_right_corner_size };
+    corner_clipper.sample_canvas_bottom_left_rect = { bitmap_locations.bottom_left, bottom_left_corner_size };
+
+    corner_clipper.corners_sample_canvas = AccelGfx::Canvas::create(sampling_config.corners_bitmap_size);
+    auto corner_painter = AccelGfx::Painter::create(m_context, *corner_clipper.corners_sample_canvas);
+    corner_painter->clear(Color::White);
+
+    corner_painter->fill_rect_with_rounded_corners(
+        Gfx::IntRect { { 0, 0 }, sampling_config.corners_bitmap_size },
+        Color::Transparent,
+        { static_cast<float>(top_left.horizontal_radius), static_cast<float>(top_left.vertical_radius) },
+        { static_cast<float>(top_right.horizontal_radius), static_cast<float>(top_right.vertical_radius) },
+        { static_cast<float>(bottom_right.horizontal_radius), static_cast<float>(bottom_right.vertical_radius) },
+        { static_cast<float>(bottom_left.horizontal_radius), static_cast<float>(bottom_left.vertical_radius) },
+        AccelGfx::Painter::BlendingMode::AlphaOverride);
+
+    auto const& target_canvas = painter().canvas();
+    if (!corner_clipper.sample_canvas_top_left_rect.is_empty())
+        corner_painter->blit_canvas(corner_clipper.sample_canvas_top_left_rect, target_canvas, painter().transform().map(corner_clipper.page_top_left_rect), 1.0f, {}, AccelGfx::Painter::BlendingMode::AlphaPreserve);
+    if (!corner_clipper.sample_canvas_top_right_rect.is_empty())
+        corner_painter->blit_canvas(corner_clipper.sample_canvas_top_right_rect, target_canvas, painter().transform().map(corner_clipper.page_top_right_rect), 1.0f, {}, AccelGfx::Painter::BlendingMode::AlphaPreserve);
+    if (!corner_clipper.sample_canvas_bottom_right_rect.is_empty())
+        corner_painter->blit_canvas(corner_clipper.sample_canvas_bottom_right_rect, target_canvas, painter().transform().map(corner_clipper.page_bottom_right_rect), 1.0f, {}, AccelGfx::Painter::BlendingMode::AlphaPreserve);
+    if (!corner_clipper.sample_canvas_bottom_left_rect.is_empty())
+        corner_painter->blit_canvas(corner_clipper.sample_canvas_bottom_left_rect, target_canvas, painter().transform().map(corner_clipper.page_bottom_left_rect), 1.0f, {}, AccelGfx::Painter::BlendingMode::AlphaPreserve);
+
     return CommandResult::Continue;
 }
 
-CommandResult PaintingCommandExecutorGPU::blit_corner_clipping(u32)
+CommandResult PaintingCommandExecutorGPU::blit_corner_clipping(u32 id)
 {
-    // FIXME
+    auto const& corner_clipper = *m_corner_clippers[id];
+    auto const& corner_sample_canvas = *corner_clipper.corners_sample_canvas;
+    if (!corner_clipper.sample_canvas_top_left_rect.is_empty())
+        painter().blit_canvas(corner_clipper.page_top_left_rect, corner_sample_canvas, corner_clipper.sample_canvas_top_left_rect);
+    if (!corner_clipper.sample_canvas_top_right_rect.is_empty())
+        painter().blit_canvas(corner_clipper.page_top_right_rect, corner_sample_canvas, corner_clipper.sample_canvas_top_right_rect);
+    if (!corner_clipper.sample_canvas_bottom_right_rect.is_empty())
+        painter().blit_canvas(corner_clipper.page_bottom_right_rect, corner_sample_canvas, corner_clipper.sample_canvas_bottom_right_rect);
+    if (!corner_clipper.sample_canvas_bottom_left_rect.is_empty())
+        painter().blit_canvas(corner_clipper.page_bottom_left_rect, corner_sample_canvas, corner_clipper.sample_canvas_bottom_left_rect);
+
+    m_corner_clippers[id].clear();
+
     return CommandResult::Continue;
 }
 

Userland/Libraries/LibWeb/Painting/PaintingCommandExecutorGPU.h

@@ -71,10 +71,25 @@ private:
         int stacking_context_depth { 0 };
     };
 
+    struct BorderRadiusCornerClipper {
+        RefPtr<AccelGfx::Canvas> corners_sample_canvas;
+
+        Gfx::FloatRect page_top_left_rect;
+        Gfx::FloatRect page_top_right_rect;
+        Gfx::FloatRect page_bottom_right_rect;
+        Gfx::FloatRect page_bottom_left_rect;
+
+        Gfx::FloatRect sample_canvas_top_left_rect;
+        Gfx::FloatRect sample_canvas_top_right_rect;
+        Gfx::FloatRect sample_canvas_bottom_right_rect;
+        Gfx::FloatRect sample_canvas_bottom_left_rect;
+    };
+
     [[nodiscard]] AccelGfx::Painter const& painter() const { return *m_stacking_contexts.last().painter; }
     [[nodiscard]] AccelGfx::Painter& painter() { return *m_stacking_contexts.last().painter; }
 
     Vector<StackingContext> m_stacking_contexts;
+    Vector<OwnPtr<BorderRadiusCornerClipper>> m_corner_clippers;
 };
 
 }