opacity pressure and jitter, initial direction

src/node_stroke_preview.h

@@ -9,7 +9,8 @@ class NodeStrokePreview : public NodeBorder
     struct StrokeFrame
     {
         glm::vec4 col;
-        float pressure;
+        float flow;
+        float opacity;
         std::array<vertex_t, 4> shapes;
         glm::vec4 m_mixer_rect;
     };