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

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.
2024-07-23 11:04:40 +00:00 · 2023-08-03 12:18:17 +02:00 · 2023-08-03 12:18:17 +02:00 · 220e34b69d
parent e689422564
commit 220e34b69d
9 changed files with 159 additions and 9 deletions
--- a/Base/res/html/misc/canvas-text.html
+++ b/Base/res/html/misc/canvas-text.html
@ -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>
--- a/Userland/Libraries/LibWeb/Forward.h
+++ b/Userland/Libraries/LibWeb/Forward.h
@ -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;
--- a/Userland/Libraries/LibWeb/HTML/Canvas/CanvasPathDrawingStyles.idl
+++ b/Userland/Libraries/LibWeb/HTML/Canvas/CanvasPathDrawingStyles.idl
@ -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 {
--- a/Userland/Libraries/LibWeb/HTML/Canvas/CanvasState.h
+++ b/Userland/Libraries/LibWeb/HTML/Canvas/CanvasState.h
@ -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; }
--- a/Userland/Libraries/LibWeb/HTML/Canvas/CanvasTextDrawingStyles.h
+++ b/Userland/Libraries/LibWeb/HTML/Canvas/CanvasTextDrawingStyles.h
@ -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(); }
+};
+
+}
--- a/Userland/Libraries/LibWeb/HTML/Canvas/CanvasTextDrawingStyles.idl
+++ b/Userland/Libraries/LibWeb/HTML/Canvas/CanvasTextDrawingStyles.idl
@ -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")
+};
--- a/Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.cpp
+++ b/Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.cpp
@ -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));
--- a/Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.h
+++ b/Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.h
@ -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);

--- a/Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.idl
+++ b/Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.idl
@ -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;