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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.
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Userland/Libraries/LibWeb/HTML/TextMetrics.h
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Userland/Libraries/LibWeb/HTML/TextMetrics.h
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/*
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* Copyright (c) 2021, sin-ack <sin-ack@protonmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <LibJS/Heap/Handle.h>
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#include <LibWeb/Bindings/Wrappable.h>
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namespace Web::HTML {
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class TextMetrics
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: public RefCounted<TextMetrics>
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, public Bindings::Wrappable {
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public:
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using WrapperType = Bindings::TextMetricsWrapper;
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static RefPtr<TextMetrics> create();
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double width() const { return m_width; }
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double actual_bounding_box_left() const { return m_actual_bounding_box_left; }
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double actual_bounding_box_right() const { return m_actual_bounding_box_right; }
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double font_bounding_box_ascent() const { return m_font_bounding_box_ascent; }
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double font_bounding_box_descent() const { return m_font_bounding_box_descent; }
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double actual_bounding_box_ascent() const { return m_actual_bounding_box_ascent; }
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double actual_bounding_box_descent() const { return m_actual_bounding_box_descent; }
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double em_height_ascent() const { return m_em_height_ascent; }
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double em_height_descent() const { return m_em_height_descent; }
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double hanging_baseline() const { return m_hanging_baseline; }
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double alphabetic_baseline() const { return m_alphabetic_baseline; }
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double ideographic_baseline() const { return m_ideographic_baseline; }
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void set_width(double width) { m_width = width; }
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void set_actual_bounding_box_left(double left) { m_actual_bounding_box_left = left; }
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void set_actual_bounding_box_right(double right) { m_actual_bounding_box_right = right; }
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void set_font_bounding_box_ascent(double ascent) { m_font_bounding_box_ascent = ascent; }
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void set_font_bounding_box_descent(double descent) { m_font_bounding_box_descent = descent; }
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void set_actual_bounding_box_ascent(double ascent) { m_actual_bounding_box_ascent = ascent; }
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void set_actual_bounding_box_descent(double descent) { m_actual_bounding_box_descent = descent; }
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void set_em_height_ascent(double ascent) { m_em_height_ascent = ascent; }
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void set_em_height_descent(double descent) { m_em_height_descent = descent; }
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void set_hanging_baseline(double baseline) { m_hanging_baseline = baseline; }
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void set_alphabetic_baseline(double baseline) { m_alphabetic_baseline = baseline; }
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void set_ideographic_baseline(double baseline) { m_ideographic_baseline = baseline; }
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private:
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explicit TextMetrics() { }
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double m_width { 0 };
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double m_actual_bounding_box_left { 0 };
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double m_actual_bounding_box_right { 0 };
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double m_font_bounding_box_ascent { 0 };
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double m_font_bounding_box_descent { 0 };
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double m_actual_bounding_box_ascent { 0 };
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double m_actual_bounding_box_descent { 0 };
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double m_em_height_ascent { 0 };
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double m_em_height_descent { 0 };
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double m_hanging_baseline { 0 };
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double m_alphabetic_baseline { 0 };
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double m_ideographic_baseline { 0 };
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};
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}
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