Fix crash when quitting mid-render

gui/include/gui/shape.hpp

@@ -112,6 +112,15 @@ class Shape : public QObject, QOpenGLFunctions
      */
     void setHover(bool h);
 
+    /*
+     *  Destroys all OpenGL objects associated with this shape
+     *
+     *  This must be called when the context is current, and must
+     *  be called before the context is destroyed (otherwise, the Shape
+     *  destructor may try to use a now-destroyed context)
+     */
+    void freeGL();
+
 signals:
     void gotMesh();
     void redraw();

gui/include/gui/view.hpp

@@ -46,6 +46,15 @@ class View : public QOpenGLWidget, QOpenGLFunctions
      */
     void cancelShapes();
 
+    /*
+     *  In the destructor, free the OpenGL data associated with
+     *  all children Shapes (because there could be shapes that
+     *  aren't explicitly stored in the object, which will be freed
+     *  by the QObject destructor, which runs after the OpenGL context
+     *  is gone).
+     */
+    ~View();
+
 public slots:
     void setShapes(QList<Shape*> shapes);
     void openSettings();

gui/src/shape.cpp

@@ -303,6 +303,18 @@ void Shape::onFutureFinished()
     }
 }
 
+void Shape::freeGL()
+{
+    if (gl_ready)
+    {
+        vao.destroy();
+        vert_vbo.destroy();
+        tri_vbo.destroy();
+
+        gl_ready = false;
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // This function is called in a separate thread:
 Kernel::Mesh* Shape::renderMesh(QPair<Settings, int> s)

gui/src/view.cpp

@@ -45,6 +45,16 @@ View::View(QWidget* parent)
     connect(&pick_timer, &QTimer::timeout, this, &View::redrawPicker);
 }
 
+View::~View()
+{
+    makeCurrent();
+    for (auto s : findChildren<Shape*>())
+    {
+        s->freeGL();
+    }
+    doneCurrent();
+}
+
 void View::setShapes(QList<Shape*> new_shapes)
 {
     // Pack tree IDs into a pair of sets for fast checking