progs/perf: also request a stencil buffer
diff --git a/progs/perf/glmain.c b/progs/perf/glmain.c
index a167be0..22b404e 100644
--- a/progs/perf/glmain.c
+++ b/progs/perf/glmain.c
@@ -253,7 +253,7 @@
 {
    glutInit(&argc, argv);
    glutInitWindowSize(WinWidth, WinHeight);
-   glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
+   glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH | GLUT_STENCIL);
    Win = glutCreateWindow(argv[0]);
    glewInit();
    glutReshapeFunc(Reshape);