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LibWeb: Add Canvas Context2D basic text align and text baseline support

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Add the CanvasTextDrawingStyles mixin with the textAlign and
textBaseline attributes. Update fill_text in CanvasRenderingContext2D
to move the text rect by the text align and text baseline attributes.
Wrote a simple HTML example to showcase the new features.
This commit is contained in:
Bastiaan van der Plaat 2023-08-03 12:18:17 +02:00 committed by Andreas Kling
parent e689422564
commit 220e34b69d
Notes: sideshowbarker 2024-07-17 08:55:54 +09:00 
Author: https://github.com/bplaat
Commit: https://github.com/SerenityOS/serenity/commit/220e34b69d
Pull-request: https://github.com/SerenityOS/serenity/pull/20342
9 changed files with 159 additions and 9 deletions
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66
Base/res/html/misc/canvas-text.html Normal file
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@ -0,0 +1,66 @@
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Canvas Text Examples</title>
</head>
<body>
<h1>Canvas Text Examples</h1>
<em>Canvas text-align</em><br>
<canvas id="canvas0" style="border: 1px solid black;"></canvas><br><br>
<script>
(function () {
const canvas = document.getElementById('canvas0');
const ctx = canvas.getContext('2d');
ctx.strokeStyle = 'red';
ctx.beginPath();
ctx.moveTo(canvas.width / 2, 0);
ctx.lineTo(canvas.width / 2, canvas.height);
ctx.stroke();
ctx.font = '16px sans-serif';
ctx.textBaseline = 'top';
const alignments = ['left', 'center', 'right', 'start', 'end'];
let y = 8;
for (const alignment of alignments) {
ctx.textAlign = alignment;
ctx.fillText(`Text align: ${alignment}`, canvas.width / 2, y);
y += 16 + 8;
}
})();
</script>
<em>Canvas text-baseline</em><br>
<canvas id="canvas1" width="1000" style="border: 1px solid black;"></canvas><br><br>
<script>
(function () {
const canvas = document.getElementById('canvas1');
const ctx = canvas.getContext('2d');
ctx.strokeStyle = 'red';
ctx.beginPath();
ctx.moveTo(0, canvas.height / 2);
ctx.lineTo(canvas.width, canvas.height / 2);
ctx.stroke();
ctx.font = '12px sans-serif';
ctx.textAlign = 'left';
const baselines = ['top', 'hanging', 'middle', 'alphabetic', 'ideographic', 'bottom'];
let x = 8;
for (const baseline of baselines) {
ctx.textBaseline = baseline;
ctx.fillText(`Baseline: ${baseline}`, x, canvas.height / 2);
x += canvas.width / baselines.length;
}
})();
</script>
</body>
</html>

2
Userland/Libraries/LibWeb/Forward.h
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@ -36,6 +36,8 @@ class OptionConstructor;
enum class AudioContextLatencyCategory;
enum class CanPlayTypeResult;
enum class CanvasFillRule;
enum class CanvasTextAlign;
enum class CanvasTextBaseline;
enum class DOMParserSupportedType;
enum class EndingType;
enum class ImageSmoothingQuality;

7
Userland/Libraries/LibWeb/HTML/Canvas/CanvasPathDrawingStyles.idl
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@ -1,13 +1,6 @@
// https://html.spec.whatwg.org/multipage/canvas.html#canvaslinecap
enum CanvasLineCap { "butt", "round", "square" };
enum CanvasLineJoin { "round", "bevel", "miter" };
enum CanvasTextAlign { "start", "end", "left", "right", "center" };
enum CanvasTextBaseline { "top", "hanging", "middle", "alphabetic", "ideographic", "bottom" };
enum CanvasDirection { "ltr", "rtl", "inherit" };
enum CanvasFontKerning { "auto", "normal", "none" };
enum CanvasFontStretch { "ultra-condensed", "extra-condensed", "condensed", "semi-condensed", "normal", "semi-expanded", "expanded", "extra-expanded", "ultra-expanded" };
enum CanvasFontVariantCaps { "normal", "small-caps", "all-small-caps", "petite-caps", "all-petite-caps", "unicase", "titling-caps" };
enum CanvasTextRendering { "auto", "optimizeSpeed", "optimizeLegibility", "geometricPrecision" };
// https://html.spec.whatwg.org/multipage/canvas.html#canvaspathdrawingstyles
interface mixin CanvasPathDrawingStyles {

2
Userland/Libraries/LibWeb/HTML/Canvas/CanvasState.h
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@ -80,6 +80,8 @@ public:
Bindings::ImageSmoothingQuality image_smoothing_quality { Bindings::ImageSmoothingQuality::Low };
float global_alpha = { 1 };
Optional<CanvasClip> clip;
Bindings::CanvasTextAlign text_align { Bindings::CanvasTextAlign::Start };
Bindings::CanvasTextBaseline text_baseline { Bindings::CanvasTextBaseline::Alphabetic };
};
DrawingState& drawing_state() { return m_drawing_state; }
DrawingState const& drawing_state() const { return m_drawing_state; }

33
Userland/Libraries/LibWeb/HTML/Canvas/CanvasTextDrawingStyles.h Normal file
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@ -0,0 +1,33 @@
/*
* Copyright (c) 2023, Bastiaan van der Plaat <bastiaan.v.d.plaat@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <LibWeb/HTML/Canvas/CanvasState.h>
namespace Web::HTML {
// https://html.spec.whatwg.org/multipage/canvas.html#canvastextdrawingstyles
template<typename IncludingClass>
class CanvasTextDrawingStyles {
public:
~CanvasTextDrawingStyles() = default;
void set_text_align(Bindings::CanvasTextAlign text_align) { my_drawing_state().text_align = text_align; }
Bindings::CanvasTextAlign text_align() const { return my_drawing_state().text_align; }
void set_text_baseline(Bindings::CanvasTextBaseline text_baseline) { my_drawing_state().text_baseline = text_baseline; }
Bindings::CanvasTextBaseline text_baseline() const { return my_drawing_state().text_baseline; }
protected:
CanvasTextDrawingStyles() = default;
private:
CanvasState::DrawingState& my_drawing_state() { return reinterpret_cast<IncludingClass&>(*this).drawing_state(); }
CanvasState::DrawingState const& my_drawing_state() const { return reinterpret_cast<IncludingClass const&>(*this).drawing_state(); }
};
}

22
Userland/Libraries/LibWeb/HTML/Canvas/CanvasTextDrawingStyles.idl Normal file
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@ -0,0 +1,22 @@
// https://html.spec.whatwg.org/multipage/canvas.html#canvastextalign
// enum CanvasTextAlign { "start", "end", "left", "right", "center" };
// enum CanvasTextBaseline { "top", "hanging", "middle", "alphabetic", "ideographic", "bottom" };
enum CanvasDirection { "ltr", "rtl", "inherit" };
enum CanvasFontKerning { "auto", "normal", "none" };
enum CanvasFontStretch { "ultra-condensed", "extra-condensed", "condensed", "semi-condensed", "normal", "semi-expanded", "expanded", "extra-expanded", "ultra-expanded" };
enum CanvasFontVariantCaps { "normal", "small-caps", "all-small-caps", "petite-caps", "all-petite-caps", "unicase", "titling-caps" };
enum CanvasTextRendering { "auto", "optimizeSpeed", "optimizeLegibility", "geometricPrecision" };
// https://html.spec.whatwg.org/multipage/canvas.html#canvastextdrawingstyles
interface mixin CanvasTextDrawingStyles {
// FIXME: attribute DOMString font; // (default 10px sans-serif)
attribute CanvasTextAlign textAlign; // (default: "start")
attribute CanvasTextBaseline textBaseline; // (default: "alphabetic")
// FIXME: attribute CanvasDirection direction; // (default: "inherit")
// FIXME: attribute DOMString letterSpacing; // (default: "0px")
// FIXME: attribute CanvasFontKerning fontKerning; // (default: "auto")
// FIXME: attribute CanvasFontStretch fontStretch; // (default: "normal")
// FIXME: attribute CanvasFontVariantCaps fontVariantCaps; // (default: "normal")
// FIXME: attribute CanvasTextRendering textRendering; // (default: "auto")
// FIXME: attribute DOMString wordSpacing; // (default: "0px")
};

25
Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.cpp
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@ -205,7 +205,32 @@ void CanvasRenderingContext2D::fill_text(DeprecatedString const& text, float x,
draw_clipped([&](auto& painter) {
auto& drawing_state = this->drawing_state();
auto& base_painter = painter.underlying_painter();
auto text_rect = Gfx::FloatRect(x, y, max_width.has_value() ? static_cast<float>(max_width.value()) : base_painter.font().width(text), base_painter.font().pixel_size());
// Apply text align to text_rect
// FIXME: CanvasTextAlign::Start and CanvasTextAlign::End currently do not nothing for right-to-left languages:
// https://html.spec.whatwg.org/multipage/canvas.html#dom-context-2d-textalign-start
// Default alignment of draw_text is left so do nothing by CanvasTextAlign::Start and CanvasTextAlign::Left
if (drawing_state.text_align == Bindings::CanvasTextAlign::Center) {
text_rect.translate_by(-text_rect.width() / 2, 0);
}
if (drawing_state.text_align == Bindings::CanvasTextAlign::End || drawing_state.text_align == Bindings::CanvasTextAlign::Right) {
text_rect.translate_by(-text_rect.width(), 0);
}
// Apply text baseline to text_rect
// FIXME: Implement CanvasTextBasline::Hanging, Bindings::CanvasTextAlign::Alphabetic and Bindings::CanvasTextAlign::Ideographic for real
// right now they are just handled as textBaseline = top or bottom.
// https://html.spec.whatwg.org/multipage/canvas.html#dom-context-2d-textbaseline-hanging
// Default baseline of draw_text is top so do nothing by CanvasTextBaseline::Top and CanvasTextBasline::Hanging
if (drawing_state.text_baseline == Bindings::CanvasTextBaseline::Middle) {
text_rect.translate_by(0, -base_painter.font().pixel_size() / 2);
}
if (drawing_state.text_baseline == Bindings::CanvasTextBaseline::Alphabetic || drawing_state.text_baseline == Bindings::CanvasTextBaseline::Ideographic || drawing_state.text_baseline == Bindings::CanvasTextBaseline::Bottom) {
text_rect.translate_by(0, -base_painter.font().pixel_size());
}
auto transformed_rect = drawing_state.transform.map(text_rect);
auto color = drawing_state.fill_style.to_color_but_fixme_should_accept_any_paint_style();
base_painter.draw_text(transformed_rect, text, Gfx::TextAlignment::TopLeft, color.with_opacity(drawing_state.global_alpha));

4
Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.h
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@ -28,6 +28,7 @@
#include <LibWeb/HTML/Canvas/CanvasRect.h>
#include <LibWeb/HTML/Canvas/CanvasState.h>
#include <LibWeb/HTML/Canvas/CanvasText.h>
#include <LibWeb/HTML/Canvas/CanvasTextDrawingStyles.h>
#include <LibWeb/HTML/Canvas/CanvasTransform.h>
#include <LibWeb/HTML/CanvasGradient.h>
#include <LibWeb/Layout/InlineNode.h>
@ -53,7 +54,8 @@ class CanvasRenderingContext2D
, public CanvasImageData
, public CanvasImageSmoothing
, public CanvasCompositing
, public CanvasPathDrawingStyles<CanvasRenderingContext2D> {
, public CanvasPathDrawingStyles<CanvasRenderingContext2D>
, public CanvasTextDrawingStyles<CanvasRenderingContext2D> {
WEB_PLATFORM_OBJECT(CanvasRenderingContext2D, Bindings::PlatformObject);

7
Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.idl
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@ -7,6 +7,7 @@
#import <HTML/Canvas/CanvasImageSmoothing.idl>
#import <HTML/Canvas/CanvasPath.idl>
#import <HTML/Canvas/CanvasPathDrawingStyles.idl>
#import <HTML/Canvas/CanvasTextDrawingStyles.idl>
#import <HTML/Canvas/CanvasRect.idl>
#import <HTML/Canvas/CanvasState.idl>
#import <HTML/Canvas/CanvasText.idl>
@ -14,6 +15,10 @@
enum ImageSmoothingQuality { "low", "medium", "high" };
// FIXME: This should be in CanvasTextDrawingStyles.idl but then it is not exported
enum CanvasTextAlign { "start", "end", "left", "right", "center" };
enum CanvasTextBaseline { "top", "hanging", "middle", "alphabetic", "ideographic", "bottom" };
// https://html.spec.whatwg.org/multipage/canvas.html#canvasrenderingcontext2d
[Exposed=Window]
interface CanvasRenderingContext2D {
@ -34,5 +39,5 @@ CanvasRenderingContext2D includes CanvasText;
CanvasRenderingContext2D includes CanvasDrawImage;
CanvasRenderingContext2D includes CanvasImageData;
CanvasRenderingContext2D includes CanvasPathDrawingStyles;
// FIXME: CanvasRenderingContext2D includes CanvasTextDrawingStyles;
CanvasRenderingContext2D includes CanvasTextDrawingStyles;
CanvasRenderingContext2D includes CanvasPath;