Bevel shape outline corners beyond threshold

Inspired by stroke-miterlimit SVG attribute.

src/SFML/Graphics/Shape.cpp

@@ -291,8 +291,10 @@ void Shape::updateOutline()
     }
 
     const std::size_t count = m_vertices.getVertexCount() - 2;
-    m_outlineVertices.resize((count + 1) * 2);
+    m_outlineVertices.resize((count + 1) * 2); // We need at least that many vertices.
+                                               // We will add two more vertices each time we need a bevel.
 
+    std::size_t outlineIndex = 0;
     for (std::size_t i = 0; i < count; ++i)
     {
         const std::size_t index = i + 1;
@@ -313,18 +315,29 @@ void Shape::updateOutline()
         if (n2.dot(m_vertices[0].position - p1) > 0)
             n2 = -n2;
 
-        // Combine them to get the extrusion direction
-        const float    factor = 1.f + (n1.x * n2.x + n1.y * n2.y);
-        const Vector2f normal = (n1 + n2) / factor;
-
         // Update the outline points
-        m_outlineVertices[i * 2 + 0].position = p1;
-        m_outlineVertices[i * 2 + 1].position = p1 + normal * m_outlineThickness;
+        const float     factor     = 1.f + n1.dot(n2);
+        constexpr float miterLimit = 4.f;
+        if (miterLimit * miterLimit * factor < 2.f) // Note this is true if factor is 0
+        {
+            // The limit on the ratio of the miter length to the outline width is exceeded so add a bevel
+            m_outlineVertices.resize(m_outlineVertices.getVertexCount() + 2);
+            m_outlineVertices[outlineIndex++].position = p1;
+            m_outlineVertices[outlineIndex++].position = p1 + n1 * m_outlineThickness;
+            m_outlineVertices[outlineIndex++].position = p1;
+            m_outlineVertices[outlineIndex++].position = p1 + n2 * m_outlineThickness;
+        }
+        else
+        {
+            const Vector2f extrusion                   = (n1 + n2) / factor;
+            m_outlineVertices[outlineIndex++].position = p1;
+            m_outlineVertices[outlineIndex++].position = p1 + extrusion * m_outlineThickness;
+        }
     }
 
     // Duplicate the first point at the end, to close the outline
-    m_outlineVertices[count * 2 + 0].position = m_outlineVertices[0].position;
-    m_outlineVertices[count * 2 + 1].position = m_outlineVertices[1].position;
+    m_outlineVertices[outlineIndex++].position = m_outlineVertices[0].position;
+    m_outlineVertices[outlineIndex++].position = m_outlineVertices[1].position;
 
     // Update outline colors
     updateOutlineColors();