App::I static singleton to pointer

src/node_viewport.cpp

@@ -18,7 +18,7 @@ void NodeViewport::draw()
     glClear(GL_COLOR_BUFFER_BIT);
     auto box = m_clip * root()->m_zoom;
     glm::ivec4 c = (glm::ivec4)glm::vec4(box.x, (int)(vp[3] - box.y - box.w), box.z, box.w);
-    glViewport(c.x + App::I.off_x, c.y + App::I.off_y, c.z, c.w);
+    glViewport(c.x + App::I->off_x, c.y + App::I->off_y, c.z, c.w);
     TextureManager::get(m_tex_id).bind();
     m_sampler->bind(0);
     glEnable(GL_BLEND);