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LibWeb: Implement CanvasRenderingContext2D.measureText

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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.
This commit is contained in:
sin-ack 2021-12-30 22:15:38 +00:00 • committed by Linus Groh
parent 732e41714a
commit 9121cc7cae
10 changed files with 253 additions and 0 deletions
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16
Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.h
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@ -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();