[vlc-devel] [PATCH 2/2] egl: tune eglTerminate behaviour with display_reference availability

[Alexandre Janniaux]

EGL_KHR_display_reference specifies the behaviour of eglTerminate
with regards to reference counting. In addition, it specifies that
the default is that reference counting is disabled X11 or wayland,
but enabled on Android.

As we can prevent EGL GL provider from terminating its state, it
makes sure the state is correctly refcounted in any case.
---
 modules/video_output/opengl/egl.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/modules/video_output/opengl/egl.c b/modules/video_output/opengl/egl.c
index 6d6ab05738f..dd8e0cf9887 100644
--- a/modules/video_output/opengl/egl.c
+++ b/modules/video_output/opengl/egl.c
@@ -58,6 +58,7 @@ typedef struct vlc_gl_sys_t
     PFNEGLDESTROYIMAGEKHRPROC   eglDestroyImageKHR;
 
     bool prevent_terminate;
+    bool has_display_reference;
 } vlc_gl_sys_t;
 
 static int MakeCurrent (vlc_gl_t *gl)
@@ -188,8 +189,10 @@ static void Close(vlc_gl_t *gl)
         if (sys->surface != EGL_NO_SURFACE)
             eglDestroySurface(sys->display, sys->surface);
 
-        /* Kill the egl state only if we own it. */
-        if (!sys->prevent_terminate)
+        /* If has_display_reference == true, sys->display is refcounted by
+         * eglInitialize and eglTerminate, so call it anyway.
+         * Otherwise, kill the egl state only if we own it. */
+        if (sys->has_display_reference || !sys->prevent_terminate)
             eglTerminate(sys->display);
         eglReleaseThread();
     }
@@ -224,6 +227,7 @@ static int Open(vlc_gl_t *gl, const struct gl_api *api,
     sys->surface = EGL_NO_SURFACE;
     sys->eglCreateImageKHR = NULL;
     sys->eglDestroyImageKHR = NULL;
+    sys->has_display_reference = false;
 
     vout_window_t *wnd = gl->surface;
     EGLSurface (*createSurface)(EGLDisplay, EGLConfig, void *, const EGLint *)
@@ -234,6 +238,21 @@ static int Open(vlc_gl_t *gl, const struct gl_api *api,
      * the associated EGL display. */
     sys->prevent_terminate = var_GetBool(wnd, "egl-prevent-terminate");
 
+    /* See https://www.khronos.org/registry/EGL/extensions/KHR/EGL_KHR_display_reference.txt */
+    /* If EGL_KHR_display_reference is not present, eglTerminate will
+     * terminate the EGLDisplay which is shared between all clients.
+     * This extension turns the behaviour of eglTerminate into reference
+     * counting mode and prevents this issues.
+     * TODO: currently, we're using the default behaviour of this extension. */
+#ifdef USE_PLATFORM_ANDROID
+    sys->has_display_reference = true; /* enforced by Android */
+#else
+    /* If we don't conditionnaly add the EGL_TRACK_REFERENCE_KHR, EGL_TRUE
+     * parameter to display query parameters, the default is false for other
+     * platforms. */
+    sys->has_display_reference = false;
+#endif
+
 #ifdef USE_PLATFORM_X11
     sys->x11 = NULL;
 
-- 
2.23.0