LibGfx: Implement PaintStyle for SVG linear gradients

Userland/Libraries/LibGfx/PaintStyle.h

@@ -243,4 +243,49 @@ private:
     float m_end_radius { 0.0f };
 };
 
+// The following paint styles implement the gradients required for SVGs
+
+class SVGGradientPaintStyle : public GradientPaintStyle {
+public:
+    void set_gradient_transform(Gfx::AffineTransform transform)
+    {
+        m_gradient_transform = transform;
+    }
+
+    Optional<Gfx::AffineTransform> const& gradient_transform() const { return m_gradient_transform; }
+
+private:
+    Optional<Gfx::AffineTransform> m_gradient_transform {};
+};
+
+class SVGLinearGradientPaintStyle final : public SVGGradientPaintStyle {
+public:
+    static ErrorOr<NonnullRefPtr<SVGLinearGradientPaintStyle>> create(FloatPoint p0, FloatPoint p1)
+    {
+        return adopt_nonnull_ref_or_enomem(new (nothrow) SVGLinearGradientPaintStyle(p0, p1));
+    }
+
+    void set_start_point(FloatPoint start_point)
+    {
+        m_p0 = start_point;
+    }
+
+    void set_end_point(FloatPoint end_point)
+    {
+        m_p1 = end_point;
+    }
+
+private:
+    virtual void paint(IntRect physical_bounding_box, PaintFunction paint) const override;
+
+    SVGLinearGradientPaintStyle(FloatPoint p0, FloatPoint p1)
+        : m_p0(p0)
+        , m_p1(p1)
+    {
+    }
+
+    FloatPoint m_p0;
+    FloatPoint m_p1;
+};
+
 }