vo_opengl: error out gracefully when trying to use FBOs without FBO API

This can for example happen with vo_opengl_cb, if it is used with a GL
implementation that does not supports FBOs. (mpv itself should never
attempt to use FBOs if they're not available.)

Without this check it would trigger an assert() in our dummy
glBindFramebuffer wrapper.

Suspected cause of #3308, although it's still unlikely.

1 files changed, 5 insertions, 0 deletions

diff --git a/video/out/opengl/video.c b/video/out/opengl/video.c
index 7ae91eed0d..468bee90b5 100644
--- a/video/out/opengl/video.c
+++ b/video/out/opengl/video.c
@@ -2667,6 +2667,11 @@ void gl_video_render_frame(struct gl_video *p, struct vo_frame *frame, int fbo)
     GL *gl = p->gl;
     struct video_image *vimg = &p->image;
 
+    if (fbo && !(gl->mpgl_caps & MPGL_CAP_FB)) {
+        MP_FATAL(p, "Rendering to FBO requested, but no FBO extension found!\n");
+        return;
+    }
+
     p->broken_frame = false;
 
     gl->BindFramebuffer(GL_FRAMEBUFFER, fbo);