SDL API changes GL context to a newly created GL context, which differs
from other GL providers that don't switch context. Change SDL backend to
restore the original GL context. This allows Qemu's virtio-gpu to support
new virglrenderer async-fencing feature for Virgl contexts, otherwise
virglrenderer's vrend creates a fence-sync context on the Qemu's
main-loop thread that erroneously stays in-use by the main-loop after
creation, not allowing vrend's fence-sync thread switch to this new
context that belongs to it.

Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Yiwei Zhang <zzyiwei@gmail.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 ui/sdl2-gl.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/ui/sdl2-gl.c b/ui/sdl2-gl.c
index 5eca0248233e..fbac3edbc09d 100644
--- a/ui/sdl2-gl.c
+++ b/ui/sdl2-gl.c
@@ -139,10 +139,12 @@ QEMUGLContext sdl2_gl_create_context(DisplayGLCtx *dgc,
                                      QEMUGLParams *params)
 {
     struct sdl2_console *scon = container_of(dgc, struct sdl2_console, dgc);
-    SDL_GLContext ctx;
+    SDL_GLContext ctx, current_ctx;
 
     assert(scon->opengl);
 
+    current_ctx = SDL_GL_GetCurrentContext();
+
     SDL_GL_MakeCurrent(scon->real_window, scon->winctx);
 
     SDL_GL_SetAttribute(SDL_GL_SHARE_WITH_CURRENT_CONTEXT, 1);
@@ -167,6 +169,9 @@ QEMUGLContext sdl2_gl_create_context(DisplayGLCtx *dgc,
                             SDL_GL_CONTEXT_PROFILE_ES);
         ctx = SDL_GL_CreateContext(scon->real_window);
     }
+
+    SDL_GL_MakeCurrent(scon->real_window, current_ctx);
+
     return (QEMUGLContext)ctx;
 }
 
-- 
2.52.0