LibWeb: Implement CanvasRenderingContext2D.measureText

This requires an implementation of the "text preparation algorithm" as
specified here:

html.spec.whatwg.org/multipage/canvas.html#text-preparation-algorithm

However, we're missing a lot of things such as the
CanvasTextDrawingStyles interface, so most of the algorithm was not
implemented. Additionally, we also are not able to use a LineBox like
the algorithm suggests, because our layouting infra is not up to the
task yet. The prepare_text function does nothing other than figuring out
the width of the given text and return glyphs with offsets at the
moment.

1 files changed, 16 insertions, 0 deletions

diff --git a/Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.h b/Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.h
index 99d05f6baf..2e0d502657 100644
--- a/Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.h
+++ b/Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.h
@@ -14,6 +14,8 @@
 #include <LibGfx/Path.h>
 #include <LibWeb/Bindings/Wrappable.h>
 #include <LibWeb/DOM/ExceptionOr.h>
+#include <LibWeb/Layout/InlineNode.h>
+#include <LibWeb/Layout/LineBox.h>
 
 namespace Web::HTML {
 
@@ -78,10 +80,24 @@ public:
 
     HTMLCanvasElement* canvas() { return m_element; }
 
+    RefPtr<TextMetrics> measure_text(String const& text);
+
 private:
     explicit CanvasRenderingContext2D(HTMLCanvasElement&);
 
+    struct PreparedTextGlyph {
+        unsigned int c;
+        Gfx::IntPoint position;
+    };
+
+    struct PreparedText {
+        Vector<PreparedTextGlyph> glyphs;
+        Gfx::TextAlignment physical_alignment;
+        Gfx::IntRect bounding_box;
+    };
+
     void did_draw(const Gfx::FloatRect&);
+    PreparedText prepare_text(String const& text, float max_width = INFINITY);
 
     OwnPtr<Gfx::Painter> painter();