refactor: create GLMesh class

src/gui/viewport/ViewportGLWidget.h

@@ -4,15 +4,16 @@
 #include <iostream>
 #include <QOpenGLFunctions_3_2_Core>
 #include "gui/viewport/GLCamera.h"
+#include "gui/viewport/GLMesh.h"
 
 class ViewportGLWidget : public QOpenGLWidget, protected QOpenGLFunctions_3_2_Core
 {
 public:
     ViewportGLWidget(QWidget *parent) : QOpenGLWidget(parent) { }
     QSize sizeHint() const override { return QSize(-1, -1); }
-    GLuint vao;
     GLuint shaderProgram;
     GLCamera curCamera;
+    std::unique_ptr<GLMesh> triangleMesh_ ;
 
 protected:
     void initializeGL() override;