From fb3351402941efe6ff56f2bbdaa601ce8717471e Mon Sep 17 00:00:00 2001
From: Luke Wilde <lukew@serenityos.org>
Date: Wed, 9 Aug 2023 19:59:54 +0100
Subject: [PATCH] LibWeb: Support skew{X,Y} in stacking context transforms

https://drafts.csswg.org/css-transforms/#SkewDefined
---
 .../LibWeb/Painting/StackingContext.cpp       | 26 +++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/Userland/Libraries/LibWeb/Painting/StackingContext.cpp b/Userland/Libraries/LibWeb/Painting/StackingContext.cpp
index fadb8e655d..5246428eb2 100644
--- a/Userland/Libraries/LibWeb/Painting/StackingContext.cpp
+++ b/Userland/Libraries/LibWeb/Painting/StackingContext.cpp
@@ -341,6 +341,32 @@ Gfx::FloatMatrix4x4 StackingContext::get_transformation_matrix(CSS::Transformati
         if (count == 1)
             return Gfx::rotation_matrix({ 0.0f, 0.0f, 1.0f }, value(0));
         break;
+    case CSS::TransformFunction::Skew:
+        if (count == 1)
+            return Gfx::FloatMatrix4x4(1, tanf(value(0)), 0, 0,
+                0, 1, 0, 0,
+                0, 0, 1, 0,
+                0, 0, 0, 1);
+        if (count == 2)
+            return Gfx::FloatMatrix4x4(1, tanf(value(0)), 0, 0,
+                tanf(value(1)), 1, 0, 0,
+                0, 0, 1, 0,
+                0, 0, 0, 1);
+        break;
+    case CSS::TransformFunction::SkewX:
+        if (count == 1)
+            return Gfx::FloatMatrix4x4(1, tanf(value(0)), 0, 0,
+                0, 1, 0, 0,
+                0, 0, 1, 0,
+                0, 0, 0, 1);
+        break;
+    case CSS::TransformFunction::SkewY:
+        if (count == 1)
+            return Gfx::FloatMatrix4x4(1, 0, 0, 0,
+                tanf(value(0)), 1, 0, 0,
+                0, 0, 1, 0,
+                0, 0, 0, 1);
+        break;
     default:
         dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Unhandled transformation function {}", MUST(CSS::TransformationStyleValue::create(transformation.function, {}))->to_string());
     }