implement the complete stroke shader with custom blending mode

engine/shape.h

@@ -59,6 +59,7 @@ public:
         create_impl(w, h, div, idx, vertices);
         return create_buffers(idx, vertices, sizeof(idx), sizeof(vertices));
     }
+    void update_vertices(const glm::vec4* data);
 /*
     bool create(att::Divisions divisions, att::Width w, att::Height h)
     {