mixer working except when changing plane, previous sample does't work in this case

engine/canvas.cpp

@@ -346,12 +346,28 @@ void ui::Canvas::stroke_draw()
                 static glm::vec2 UV2[4];
                 int intersected = 0;
                 int inside = 0;
+                if (m_mixer_idle)
+                {
+                    m_mixer_sample = s;
+                    m_mixer_idle = false;
+                }
                 for (int j = 0; j < 4; j++)
                 {
                     glm::vec3 ray_origin, ray_dir;
                     point_unproject(s.pos + off[j] * glm::orientate2(-s.angle), { 0, 0, zw(m_box) }, m_mv, m_proj, ray_origin, ray_dir);
-                    UV2[j] = (s.pos + off[j]) / glm::vec2(m_mixer.getWidth(), m_mixer.getHeight());
-                    UV2[j].y = 1 - UV2[j].y;
+                    
+                    {
+                        glm::vec2 dx(m_mixer_sample.size * 0.5f, 0), dy(0, m_mixer_sample.size * 0.5f);
+                        glm::vec2 off[4] = {
+                            -dx - dy, // A - bottom-left
+                            -dx + dy, // B - top-left
+                            +dx + dy, // C - top-right
+                            +dx - dy, // D - bottom-right
+                        };
+                        UV2[j] = (m_mixer_sample.pos + off[j]) / glm::vec2(m_mixer.getWidth(), m_mixer.getHeight());
+                        UV2[j].y = 1 - UV2[j].y;
+                    }
+                    
                     glm::vec3 hit;
                     if (ray_intersect(ray_origin, ray_dir, m_plane_origin[i], m_plane_normal[i], m_plane_tangent[i], hit))
                     {
@@ -373,6 +389,8 @@ void ui::Canvas::stroke_draw()
                     }
                 }
                 
+                m_mixer_sample = s;
+
                 if (intersected < 4 || inside == 0)
                     continue;
 
@@ -521,6 +539,7 @@ void ui::Canvas::stroke_commit()
     if (!m_dirty || m_layers.empty())
         return;
 
+    m_mixer_idle = true;
     m_dirty = false;
     m_dirty_stroke = true; // new stroke ready for timelapse capture
     App::I.redraw = true;