integrate and link lib curl for android, add VAO support for brush draw, sync canvas with screen redraw instead of input events

engine/canvas.h

@@ -57,6 +57,11 @@ public:
     void stroke_update(glm::vec2 point, float pressure)
     {
         m_current_stroke->add_point(point, pressure);
+    }
+    void stroke_draw()
+    {
+        if (!(m_current_stroke && m_current_stroke->has_sample()))
+            return;
 
         m_fb.bindFramebuffer();