fix dynamic spacing with pressure

src/brush.cpp

@@ -260,6 +260,7 @@ void Stroke::add_point(glm::vec3 pos, float pressure)
     kp.dist = 0;
     m_keypoints.push_back(kp);
 
+    m_interp_main.spacing = m_step;
     m_interp_main.add(kp);
     m_interp_dir.add(kp);
 }