free resources on app destruction

src/canvas.cpp

@@ -1079,6 +1079,22 @@ void Canvas::resize(int width, int height)
     m_smask.create(width, height, "mask");
     m_unsaved = true;
 }
+
+void Canvas::destroy()
+{
+    for (int i = 0; i < 6; i++)
+    {
+        m_tmp[i].destroy();
+        m_tmp_dual[i].destroy();
+        m_tex[i].destroy();
+        m_tex2[i].destroy();
+    }
+    for (auto& l : m_layers)
+        l.destroy();
+    m_smask.destroy();
+    m_mixer.destroy();
+}
+
 bool Canvas::create(int width, int height)
 {
     m_width = width;
@@ -1097,7 +1113,7 @@ bool Canvas::create(int width, int height)
         m_tex[i].create(width, height, GL_RGBA32F);
         m_sampler_brush.create(GL_LINEAR, GL_CLAMP_TO_BORDER);
 #endif
-        m_tex2[i].create(width, height, GL_RGBA8); // TODO: destroy before recreating
+        m_tex2[i].create(width, height, GL_RGBA8);
     }
     m_sampler.create(GL_NEAREST);
     m_sampler.create(GL_LINEAR);