LibWeb: Add save and restore commands in recording painter

This change is a preparation before introducing Skia painter in an
upcoming change. It's needed because Skia does not have an API to
implement ClearClipRect command. It only allows to return previous
clip rect by popping from its internal state stack.

A bit more context: initially we had save and restore commands, but
their frequent use led to many reallocations of vector during painting
commands recording. To resolve this, we switched to SegmentedVector to
store commands list, which allows fast appends. Now, having many save
and restore commands no longer causes noticeable performance issue.

Userland/Libraries/LibWeb/Painting/AffineCommandExecutorCPU.cpp

@@ -64,16 +64,22 @@ CommandResult AffineCommandExecutorCPU::draw_scaled_immutable_bitmap(DrawScaledI
     return CommandResult::Continue;
 }
 
-CommandResult AffineCommandExecutorCPU::set_clip_rect(SetClipRect const&)
+CommandResult AffineCommandExecutorCPU::save(Save const&)
 {
-    // FIXME: Implement. The plan here is to implement https://en.wikipedia.org/wiki/Sutherland%E2%80%93Hodgman_algorithm
-    // within the rasterizer (which should work as the clip quadrilateral will always be convex).
+    m_painter.save();
     return CommandResult::Continue;
 }
 
-CommandResult AffineCommandExecutorCPU::clear_clip_rect(ClearClipRect const&)
+CommandResult AffineCommandExecutorCPU::restore(Restore const&)
 {
-    // FIXME: Implement.
+    m_painter.restore();
+    return CommandResult::Continue;
+}
+
+CommandResult AffineCommandExecutorCPU::add_clip_rect(AddClipRect const&)
+{
+    // FIXME: Implement. The plan here is to implement https://en.wikipedia.org/wiki/Sutherland%E2%80%93Hodgman_algorithm
+    // within the rasterizer (which should work as the clip quadrilateral will always be convex).
     return CommandResult::Continue;
 }
 

Userland/Libraries/LibWeb/Painting/AffineCommandExecutorCPU.h

@@ -19,8 +19,9 @@ public:
     CommandResult fill_rect(FillRect const&) override;
     CommandResult draw_scaled_bitmap(DrawScaledBitmap const&) override;
     CommandResult draw_scaled_immutable_bitmap(DrawScaledImmutableBitmap const&) override;
-    CommandResult set_clip_rect(SetClipRect const&) override;
-    CommandResult clear_clip_rect(ClearClipRect const&) override;
+    CommandResult save(Save const&) override;
+    CommandResult restore(Restore const&) override;
+    CommandResult add_clip_rect(AddClipRect const&) override;
     CommandResult push_stacking_context(PushStackingContext const&) override;
     CommandResult pop_stacking_context(PopStackingContext const&) override;
     CommandResult paint_linear_gradient(PaintLinearGradient const&) override;

Userland/Libraries/LibWeb/Painting/Command.h

@@ -92,12 +92,13 @@ struct DrawScaledImmutableBitmap {
     void translate_by(Gfx::IntPoint const& offset) { dst_rect.translate_by(offset); }
 };
 
-struct SetClipRect {
+struct Save { };
+struct Restore { };
+
+struct AddClipRect {
     Gfx::IntRect rect;
 };
 
-struct ClearClipRect { };
-
 struct StackingContextTransform {
     Gfx::FloatPoint origin;
     Gfx::FloatMatrix4x4 matrix;
@@ -372,8 +373,9 @@ using Command = Variant<
     FillRect,
     DrawScaledBitmap,
     DrawScaledImmutableBitmap,
-    SetClipRect,
-    ClearClipRect,
+    Save,
+    Restore,
+    AddClipRect,
     PushStackingContext,
     PopStackingContext,
     PaintLinearGradient,

Userland/Libraries/LibWeb/Painting/CommandExecutorCPU.cpp

@@ -107,17 +107,21 @@ CommandResult CommandExecutorCPU::draw_scaled_immutable_bitmap(DrawScaledImmutab
     return CommandResult::Continue;
 }
 
-CommandResult CommandExecutorCPU::set_clip_rect(SetClipRect const& command)
+CommandResult CommandExecutorCPU::save(Save const&)
 {
-    auto& painter = this->painter();
-    painter.clear_clip_rect();
-    painter.add_clip_rect(command.rect);
+    painter().save();
+    return CommandResult::Continue;
+}
+
+CommandResult CommandExecutorCPU::restore(Restore const&)
+{
+    painter().restore();
     return CommandResult::Continue;
 }
 
-CommandResult CommandExecutorCPU::clear_clip_rect(ClearClipRect const&)
+CommandResult CommandExecutorCPU::add_clip_rect(AddClipRect const& command)
 {
-    painter().clear_clip_rect();
+    painter().add_clip_rect(command.rect);
     return CommandResult::Continue;
 }
 

Userland/Libraries/LibWeb/Painting/CommandExecutorCPU.h

@@ -20,8 +20,9 @@ public:
     CommandResult fill_rect(FillRect const&) override;
     CommandResult draw_scaled_bitmap(DrawScaledBitmap const&) override;
     CommandResult draw_scaled_immutable_bitmap(DrawScaledImmutableBitmap const&) override;
-    CommandResult set_clip_rect(SetClipRect const&) override;
-    CommandResult clear_clip_rect(ClearClipRect const&) override;
+    CommandResult save(Save const&) override;
+    CommandResult restore(Restore const&) override;
+    CommandResult add_clip_rect(AddClipRect const&) override;
     CommandResult push_stacking_context(PushStackingContext const&) override;
     CommandResult pop_stacking_context(PopStackingContext const&) override;
     CommandResult paint_linear_gradient(PaintLinearGradient const&) override;

Userland/Libraries/LibWeb/Painting/CommandExecutorGPU.cpp

@@ -89,15 +89,21 @@ CommandResult CommandExecutorGPU::draw_scaled_immutable_bitmap(DrawScaledImmutab
     return CommandResult::Continue;
 }
 
-CommandResult CommandExecutorGPU::set_clip_rect(SetClipRect const& command)
+CommandResult CommandExecutorGPU::save(Save const&)
 {
-    painter().set_clip_rect(command.rect);
+    painter().save();
+    return CommandResult::Continue;
+}
+
+CommandResult CommandExecutorGPU::restore(Restore const&)
+{
+    painter().restore();
     return CommandResult::Continue;
 }
 
-CommandResult CommandExecutorGPU::clear_clip_rect(ClearClipRect const&)
+CommandResult CommandExecutorGPU::add_clip_rect(AddClipRect const& command)
 {
-    painter().clear_clip_rect();
+    painter().set_clip_rect(command.rect);
     return CommandResult::Continue;
 }
 

Userland/Libraries/LibWeb/Painting/CommandExecutorGPU.h

@@ -19,8 +19,9 @@ public:
     CommandResult fill_rect(FillRect const&) override;
     CommandResult draw_scaled_bitmap(DrawScaledBitmap const&) override;
     CommandResult draw_scaled_immutable_bitmap(DrawScaledImmutableBitmap const&) override;
-    CommandResult set_clip_rect(SetClipRect const&) override;
-    CommandResult clear_clip_rect(ClearClipRect const&) override;
+    CommandResult save(Save const&) override;
+    CommandResult restore(Restore const&) override;
+    CommandResult add_clip_rect(AddClipRect const&) override;
     CommandResult push_stacking_context(PushStackingContext const&) override;
     CommandResult pop_stacking_context(PopStackingContext const&) override;
     CommandResult paint_linear_gradient(PaintLinearGradient const&) override;

Userland/Libraries/LibWeb/Painting/CommandList.cpp

@@ -63,8 +63,8 @@ void CommandList::mark_unnecessary_commands()
                 m_commands[command_index].skip = true;
             }
         } else {
-            // SetClipRect and ClearClipRect commands do not produce visible output
-            auto update_clip_command = command.has<SetClipRect>() || command.has<ClearClipRect>();
+            // Save, Restore and AddClipRect commands do not produce visible output
+            auto update_clip_command = command.has<Save>() || command.has<Restore>() || command.has<AddClipRect>();
             if (sample_blit_ranges.size() > 0 && !update_clip_command) {
                 // If painting command is found for sample_under_corners command on top of the stack, then all
                 // sample_under_corners commands below should also not be skipped.
@@ -154,8 +154,9 @@ void CommandList::execute(CommandExecutor& executor)
         else HANDLE_COMMAND(FillRect, fill_rect)
         else HANDLE_COMMAND(DrawScaledBitmap, draw_scaled_bitmap)
         else HANDLE_COMMAND(DrawScaledImmutableBitmap, draw_scaled_immutable_bitmap)
-        else HANDLE_COMMAND(SetClipRect, set_clip_rect)
-        else HANDLE_COMMAND(ClearClipRect, clear_clip_rect)
+        else HANDLE_COMMAND(AddClipRect, add_clip_rect)
+        else HANDLE_COMMAND(Save, save)
+        else HANDLE_COMMAND(Restore, restore)
         else HANDLE_COMMAND(PushStackingContext, push_stacking_context)
         else HANDLE_COMMAND(PopStackingContext, pop_stacking_context)
         else HANDLE_COMMAND(PaintLinearGradient, paint_linear_gradient)

Userland/Libraries/LibWeb/Painting/CommandList.h

@@ -52,8 +52,9 @@ public:
     virtual CommandResult fill_rect(FillRect const&) = 0;
     virtual CommandResult draw_scaled_bitmap(DrawScaledBitmap const&) = 0;
     virtual CommandResult draw_scaled_immutable_bitmap(DrawScaledImmutableBitmap const&) = 0;
-    virtual CommandResult set_clip_rect(SetClipRect const&) = 0;
-    virtual CommandResult clear_clip_rect(ClearClipRect const&) = 0;
+    virtual CommandResult save(Save const&) = 0;
+    virtual CommandResult restore(Restore const&) = 0;
+    virtual CommandResult add_clip_rect(AddClipRect const&) = 0;
     virtual CommandResult push_stacking_context(PushStackingContext const&) = 0;
     virtual CommandResult pop_stacking_context(PopStackingContext const&) = 0;
     virtual CommandResult paint_linear_gradient(PaintLinearGradient const&) = 0;

Userland/Libraries/LibWeb/Painting/RecordingPainter.cpp

@@ -253,15 +253,7 @@ void RecordingPainter::draw_text_run(Gfx::IntPoint baseline_start, Gfx::GlyphRun
 
 void RecordingPainter::add_clip_rect(Gfx::IntRect const& rect)
 {
-    auto prev_clip_rect = state().clip_rect;
-    if (!state().clip_rect.has_value()) {
-        state().clip_rect = state().translation.map(rect);
-    } else {
-        state().clip_rect->intersect(state().translation.map(rect));
-    }
-
-    if (prev_clip_rect != state().clip_rect)
-        append(SetClipRect { .rect = *state().clip_rect });
+    append(AddClipRect { .rect = state().translation.map(rect) });
 }
 
 void RecordingPainter::translate(int dx, int dy)
@@ -276,22 +268,16 @@ void RecordingPainter::translate(Gfx::IntPoint delta)
 
 void RecordingPainter::save()
 {
+    append(Save {});
     m_state_stack.append(m_state_stack.last());
 }
 
 void RecordingPainter::restore()
 {
-    auto prev_clip_rect = state().clip_rect;
+    append(Restore {});
 
     VERIFY(m_state_stack.size() > 1);
     m_state_stack.take_last();
-
-    if (state().clip_rect != prev_clip_rect) {
-        if (state().clip_rect.has_value())
-            append(SetClipRect { .rect = *state().clip_rect });
-        else
-            append(ClearClipRect {});
-    }
 }
 
 void RecordingPainter::push_stacking_context(PushStackingContextParams params)