From b99c0c6a7f243f9c78f9fc2ab75d1895a79495bd Mon Sep 17 00:00:00 2001
From: Tim Ledbetter <tim.ledbetter@ladybird.org>
Date: Tue, 21 Oct 2025 10:09:46 +0100
Subject: [PATCH] LibWeb: Account for paint style and global alpha when drawing
 shadows

---
 .../LibWeb/HTML/CanvasRenderingContext2D.cpp  |  18 ++++++++-
 .../element/shadows/2d.shadow.alpha.1.txt     |   6 +++
 .../element/shadows/2d.shadow.alpha.2.txt     |   6 +++
 .../element/shadows/2d.shadow.alpha.3.txt     |   6 +++
 .../element/shadows/2d.shadow.alpha.4.txt     |   6 +++
 .../element/shadows/2d.shadow.alpha.5.txt     |   6 +++
 .../element/shadows/2d.shadow.alpha.1.html    |  33 +++++++++++++++++
 .../element/shadows/2d.shadow.alpha.2.html    |  33 +++++++++++++++++
 .../element/shadows/2d.shadow.alpha.2.png     | Bin 0 -> 206 bytes
 .../element/shadows/2d.shadow.alpha.3.html    |  35 ++++++++++++++++++
 .../element/shadows/2d.shadow.alpha.3.png     | Bin 0 -> 206 bytes
 .../element/shadows/2d.shadow.alpha.4.html    |  35 ++++++++++++++++++
 .../element/shadows/2d.shadow.alpha.4.png     | Bin 0 -> 206 bytes
 .../element/shadows/2d.shadow.alpha.5.html    |  34 +++++++++++++++++
 .../element/shadows/2d.shadow.alpha.5.png     | Bin 0 -> 206 bytes
 15 files changed, 216 insertions(+), 2 deletions(-)
 create mode 100644 Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.1.txt
 create mode 100644 Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.txt
 create mode 100644 Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.txt
 create mode 100644 Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.txt
 create mode 100644 Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.txt
 create mode 100644 Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.1.html
 create mode 100644 Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.html
 create mode 100644 Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.png
 create mode 100644 Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.html
 create mode 100644 Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.png
 create mode 100644 Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.html
 create mode 100644 Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.png
 create mode 100644 Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.html
 create mode 100644 Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.png

diff --git a/Libraries/LibWeb/HTML/CanvasRenderingContext2D.cpp b/Libraries/LibWeb/HTML/CanvasRenderingContext2D.cpp
index e851eaeed87..24cc27d27b2 100644
--- a/Libraries/LibWeb/HTML/CanvasRenderingContext2D.cpp
+++ b/Libraries/LibWeb/HTML/CanvasRenderingContext2D.cpp
@@ -1062,12 +1062,19 @@ void CanvasRenderingContext2D::paint_shadow_for_fill_internal(Gfx::Path const& p
     if (state.current_compositing_and_blending_operator == Gfx::CompositingAndBlendingOperator::Copy)
         return;
 
+    auto alpha = state.global_alpha * (state.shadow_color.alpha() / 255.0f);
+    auto fill_style_color = state.fill_style.as_color();
+    if (fill_style_color.has_value() && fill_style_color->alpha() > 0)
+        alpha = (fill_style_color->alpha() / 255.0f) * state.global_alpha;
+    if (alpha == 0.0f)
+        return;
+
     painter->save();
 
     Gfx::AffineTransform transform;
     transform.translate(state.shadow_offset_x, state.shadow_offset_y);
     painter->set_transform(transform);
-    painter->fill_path(path, state.shadow_color.with_opacity(state.global_alpha), winding_rule, state.shadow_blur, state.current_compositing_and_blending_operator);
+    painter->fill_path(path, state.shadow_color.with_opacity(alpha), winding_rule, state.shadow_blur, state.current_compositing_and_blending_operator);
 
     painter->restore();
 
@@ -1085,12 +1092,19 @@ void CanvasRenderingContext2D::paint_shadow_for_stroke_internal(Gfx::Path const&
     if (state.current_compositing_and_blending_operator == Gfx::CompositingAndBlendingOperator::Copy)
         return;
 
+    auto alpha = state.global_alpha * (state.shadow_color.alpha() / 255.0f);
+    auto fill_style_color = state.fill_style.as_color();
+    if (fill_style_color.has_value() && fill_style_color->alpha() > 0)
+        alpha = (fill_style_color->alpha() / 255.0f) * state.global_alpha;
+    if (alpha == 0.0f)
+        return;
+
     painter->save();
 
     Gfx::AffineTransform transform;
     transform.translate(state.shadow_offset_x, state.shadow_offset_y);
     painter->set_transform(transform);
-    painter->stroke_path(path, state.shadow_color.with_opacity(state.global_alpha), state.line_width, state.shadow_blur, state.current_compositing_and_blending_operator);
+    painter->stroke_path(path, state.shadow_color.with_opacity(alpha), state.line_width, state.shadow_blur, state.current_compositing_and_blending_operator);
 
     painter->restore();
 
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.1.txt b/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.1.txt
new file mode 100644
index 00000000000..04bdedfed89
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.1.txt
@@ -0,0 +1,6 @@
+Harness status: OK
+
+Found 1 tests
+
+1 Pass
+Pass	Shadow color alpha components are used
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.txt b/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.txt
new file mode 100644
index 00000000000..04bdedfed89
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.txt
@@ -0,0 +1,6 @@
+Harness status: OK
+
+Found 1 tests
+
+1 Pass
+Pass	Shadow color alpha components are used
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.txt b/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.txt
new file mode 100644
index 00000000000..70b5cfd29e8
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.txt
@@ -0,0 +1,6 @@
+Harness status: OK
+
+Found 1 tests
+
+1 Pass
+Pass	Shadows are affected by globalAlpha
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.txt b/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.txt
new file mode 100644
index 00000000000..d9404b2aa7e
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.txt
@@ -0,0 +1,6 @@
+Harness status: OK
+
+Found 1 tests
+
+1 Pass
+Pass	Shadows with alpha components are correctly affected by globalAlpha
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.txt b/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.txt
new file mode 100644
index 00000000000..2128d541275
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.txt
@@ -0,0 +1,6 @@
+Harness status: OK
+
+Found 1 tests
+
+1 Pass
+Pass	Shadows of shapes with alpha components are drawn correctly
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.1.html b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.1.html
new file mode 100644
index 00000000000..1cb62d5418b
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.1.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<!-- DO NOT EDIT! This test has been generated by /html/canvas/tools/gentest.py. -->
+<meta charset="UTF-8">
+<title>Canvas test: 2d.shadow.alpha.1</title>
+<script src="../../../../resources/testharness.js"></script>
+<script src="../../../../resources/testharnessreport.js"></script>
+<script src="../../../../html/canvas/resources/canvas-tests.js"></script>
+<link rel="stylesheet" href="../../../../html/canvas/resources/canvas-tests.css">
+<body class="show_output">
+
+<h1>2d.shadow.alpha.1</h1>
+<p class="desc">Shadow color alpha components are used</p>
+
+
+<p class="output">Actual output:</p>
+<canvas id="c" class="output" width="100" height="50"><p class="fallback">FAIL (fallback content)</p></canvas>
+<p class="output expectedtext">Expected output:<p><img src="../../../../images/green-100x50.png" class="output expected" id="expected" alt="">
+<ul id="d"></ul>
+<script>
+var t = async_test("Shadow color alpha components are used");
+_addTest(function(canvas, ctx) {
+
+  ctx.fillStyle = '#0f0';
+  ctx.fillRect(0, 0, 100, 50);
+  ctx.shadowColor = 'rgba(255, 0, 0, 0.01)';
+  ctx.shadowOffsetY = 50;
+  ctx.fillRect(0, -50, 100, 50);
+
+  _assertPixelApprox(canvas, 50,25, 0,255,0,255, 4);
+
+});
+</script>
+
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.html b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.html
new file mode 100644
index 00000000000..ee873c19742
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<!-- DO NOT EDIT! This test has been generated by /html/canvas/tools/gentest.py. -->
+<meta charset="UTF-8">
+<title>Canvas test: 2d.shadow.alpha.2</title>
+<script src="../../../../resources/testharness.js"></script>
+<script src="../../../../resources/testharnessreport.js"></script>
+<script src="../../../../html/canvas/resources/canvas-tests.js"></script>
+<link rel="stylesheet" href="../../../../html/canvas/resources/canvas-tests.css">
+<body class="show_output">
+
+<h1>2d.shadow.alpha.2</h1>
+<p class="desc">Shadow color alpha components are used</p>
+
+
+<p class="output">Actual output:</p>
+<canvas id="c" class="output" width="100" height="50"><p class="fallback">FAIL (fallback content)</p></canvas>
+<p class="output expectedtext">Expected output:<p><img src="2d.shadow.alpha.2.png" class="output expected" id="expected" alt="">
+<ul id="d"></ul>
+<script>
+var t = async_test("Shadow color alpha components are used");
+_addTest(function(canvas, ctx) {
+
+  ctx.fillStyle = '#f00';
+  ctx.fillRect(0, 0, 100, 50);
+  ctx.shadowColor = 'rgba(0, 0, 255, 0.5)';
+  ctx.shadowOffsetY = 50;
+  ctx.fillRect(0, -50, 100, 50);
+
+  _assertPixelApprox(canvas, 50,25, 127,0,127,255, 2);
+
+});
+</script>
+
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.png b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.2.png
new file mode 100644
index 0000000000000000000000000000000000000000..8764e89b371d41428f0ba45d9c0391e41b0dd8a2
GIT binary patch
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zAsLNtFF0~CC@>swFx`1^?SnX_JE{`1tKS@)`_<}!dKxQjA$wB<W6Iq>Rx^RlVeoYI
Kb6Mw<&;$U*t~bH}

literal 0
HcmV?d00001

diff --git a/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.html b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.html
new file mode 100644
index 00000000000..95e97b28691
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<!-- DO NOT EDIT! This test has been generated by /html/canvas/tools/gentest.py. -->
+<meta charset="UTF-8">
+<title>Canvas test: 2d.shadow.alpha.3</title>
+<script src="../../../../resources/testharness.js"></script>
+<script src="../../../../resources/testharnessreport.js"></script>
+<script src="../../../../html/canvas/resources/canvas-tests.js"></script>
+<link rel="stylesheet" href="../../../../html/canvas/resources/canvas-tests.css">
+<body class="show_output">
+
+<h1>2d.shadow.alpha.3</h1>
+<p class="desc">Shadows are affected by globalAlpha</p>
+
+
+<p class="output">Actual output:</p>
+<canvas id="c" class="output" width="100" height="50"><p class="fallback">FAIL (fallback content)</p></canvas>
+<p class="output expectedtext">Expected output:<p><img src="2d.shadow.alpha.3.png" class="output expected" id="expected" alt="">
+<ul id="d"></ul>
+<script>
+var t = async_test("Shadows are affected by globalAlpha");
+_addTest(function(canvas, ctx) {
+
+  ctx.fillStyle = '#f00';
+  ctx.fillRect(0, 0, 100, 50);
+  ctx.fillStyle = '#f00'; // (work around broken Firefox globalAlpha caching)
+  ctx.shadowColor = '#00f';
+  ctx.shadowOffsetY = 50;
+  ctx.globalAlpha = 0.5;
+  ctx.fillRect(0, -50, 100, 50);
+
+  _assertPixelApprox(canvas, 50,25, 127,0,127,255, 2);
+
+});
+</script>
+
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.png b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.3.png
new file mode 100644
index 0000000000000000000000000000000000000000..8764e89b371d41428f0ba45d9c0391e41b0dd8a2
GIT binary patch
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zAsLNtFF0~CC@>swFx`1^?SnX_JE{`1tKS@)`_<}!dKxQjA$wB<W6Iq>Rx^RlVeoYI
Kb6Mw<&;$U*t~bH}

literal 0
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diff --git a/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.html b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.html
new file mode 100644
index 00000000000..37547293907
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<!-- DO NOT EDIT! This test has been generated by /html/canvas/tools/gentest.py. -->
+<meta charset="UTF-8">
+<title>Canvas test: 2d.shadow.alpha.4</title>
+<script src="../../../../resources/testharness.js"></script>
+<script src="../../../../resources/testharnessreport.js"></script>
+<script src="../../../../html/canvas/resources/canvas-tests.js"></script>
+<link rel="stylesheet" href="../../../../html/canvas/resources/canvas-tests.css">
+<body class="show_output">
+
+<h1>2d.shadow.alpha.4</h1>
+<p class="desc">Shadows with alpha components are correctly affected by globalAlpha</p>
+
+
+<p class="output">Actual output:</p>
+<canvas id="c" class="output" width="100" height="50"><p class="fallback">FAIL (fallback content)</p></canvas>
+<p class="output expectedtext">Expected output:<p><img src="2d.shadow.alpha.4.png" class="output expected" id="expected" alt="">
+<ul id="d"></ul>
+<script>
+var t = async_test("Shadows with alpha components are correctly affected by globalAlpha");
+_addTest(function(canvas, ctx) {
+
+  ctx.fillStyle = '#f00';
+  ctx.fillRect(0, 0, 100, 50);
+  ctx.fillStyle = '#f00'; // (work around broken Firefox globalAlpha caching)
+  ctx.shadowColor = 'rgba(0, 0, 255, 0.707)';
+  ctx.shadowOffsetY = 50;
+  ctx.globalAlpha = 0.707;
+  ctx.fillRect(0, -50, 100, 50);
+
+  _assertPixelApprox(canvas, 50,25, 127,0,127,255, 2);
+
+});
+</script>
+
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.png b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.4.png
new file mode 100644
index 0000000000000000000000000000000000000000..8764e89b371d41428f0ba45d9c0391e41b0dd8a2
GIT binary patch
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zAsLNtFF0~CC@>swFx`1^?SnX_JE{`1tKS@)`_<}!dKxQjA$wB<W6Iq>Rx^RlVeoYI
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literal 0
HcmV?d00001

diff --git a/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.html b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.html
new file mode 100644
index 00000000000..10144359aab
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<!-- DO NOT EDIT! This test has been generated by /html/canvas/tools/gentest.py. -->
+<meta charset="UTF-8">
+<title>Canvas test: 2d.shadow.alpha.5</title>
+<script src="../../../../resources/testharness.js"></script>
+<script src="../../../../resources/testharnessreport.js"></script>
+<script src="../../../../html/canvas/resources/canvas-tests.js"></script>
+<link rel="stylesheet" href="../../../../html/canvas/resources/canvas-tests.css">
+<body class="show_output">
+
+<h1>2d.shadow.alpha.5</h1>
+<p class="desc">Shadows of shapes with alpha components are drawn correctly</p>
+
+
+<p class="output">Actual output:</p>
+<canvas id="c" class="output" width="100" height="50"><p class="fallback">FAIL (fallback content)</p></canvas>
+<p class="output expectedtext">Expected output:<p><img src="2d.shadow.alpha.5.png" class="output expected" id="expected" alt="">
+<ul id="d"></ul>
+<script>
+var t = async_test("Shadows of shapes with alpha components are drawn correctly");
+_addTest(function(canvas, ctx) {
+
+  ctx.fillStyle = '#f00';
+  ctx.fillRect(0, 0, 100, 50);
+  ctx.fillStyle = 'rgba(64, 0, 0, 0.5)';
+  ctx.shadowColor = '#00f';
+  ctx.shadowOffsetY = 50;
+  ctx.fillRect(0, -50, 100, 50);
+
+  _assertPixelApprox(canvas, 50,25, 127,0,127,255, 2);
+
+});
+</script>
+
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.png b/Tests/LibWeb/Text/input/wpt-import/html/canvas/element/shadows/2d.shadow.alpha.5.png
new file mode 100644
index 0000000000000000000000000000000000000000..8764e89b371d41428f0ba45d9c0391e41b0dd8a2
GIT binary patch
literal 206
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literal 0
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