[mutter] cogl: Use EGL_IMG_context_priority if available

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 7df86fb24646f8a19a47e54b86424048ec08e715
Author: Adam Jackson <ajax redhat com>
Date:   Wed Feb 20 17:14:14 2019 -0500

    cogl: Use EGL_IMG_context_priority if available
    
    We're the context closest to the display, so we should take priority
    over other clients.
    
    v2: Warn if we asked for a high-priority context and didn't get one.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/454

 .../winsys/cogl-winsys-egl-feature-functions.h     |  6 +++++
 cogl/cogl/winsys/cogl-winsys-egl-private.h         |  3 ++-
 cogl/cogl/winsys/cogl-winsys-egl.c                 | 29 +++++++++++++++++++++-
 3 files changed, 36 insertions(+), 2 deletions(-)
---
diff --git a/cogl/cogl/winsys/cogl-winsys-egl-feature-functions.h 
b/cogl/cogl/winsys/cogl-winsys-egl-feature-functions.h
index 17a99f269..bbe4912bc 100644
--- a/cogl/cogl/winsys/cogl-winsys-egl-feature-functions.h
+++ b/cogl/cogl/winsys/cogl-winsys-egl-feature-functions.h
@@ -147,3 +147,9 @@ COGL_WINSYS_FEATURE_BEGIN (surfaceless_context,
                            "surfaceless_context\0",
                            COGL_EGL_WINSYS_FEATURE_SURFACELESS_CONTEXT)
 COGL_WINSYS_FEATURE_END ()
+
+COGL_WINSYS_FEATURE_BEGIN (context_priority,
+                           "IMG\0",
+                           "context_priority\0",
+                           COGL_EGL_WINSYS_FEATURE_CONTEXT_PRIORITY)
+COGL_WINSYS_FEATURE_END ()
diff --git a/cogl/cogl/winsys/cogl-winsys-egl-private.h b/cogl/cogl/winsys/cogl-winsys-egl-private.h
index b98bffcf8..89fe585b9 100644
--- a/cogl/cogl/winsys/cogl-winsys-egl-private.h
+++ b/cogl/cogl/winsys/cogl-winsys-egl-private.h
@@ -105,7 +105,8 @@ typedef enum _CoglEGLWinsysFeature
   COGL_EGL_WINSYS_FEATURE_CREATE_CONTEXT                =1L<<3,
   COGL_EGL_WINSYS_FEATURE_BUFFER_AGE                    =1L<<4,
   COGL_EGL_WINSYS_FEATURE_FENCE_SYNC                    =1L<<5,
-  COGL_EGL_WINSYS_FEATURE_SURFACELESS_CONTEXT           =1L<<6
+  COGL_EGL_WINSYS_FEATURE_SURFACELESS_CONTEXT           =1L<<6,
+  COGL_EGL_WINSYS_FEATURE_CONTEXT_PRIORITY              =1L<<7,
 } CoglEGLWinsysFeature;
 
 typedef struct _CoglRendererEGL
diff --git a/cogl/cogl/winsys/cogl-winsys-egl.c b/cogl/cogl/winsys/cogl-winsys-egl.c
index e3eb311da..7b5e70bf7 100644
--- a/cogl/cogl/winsys/cogl-winsys-egl.c
+++ b/cogl/cogl/winsys/cogl-winsys-egl.c
@@ -71,6 +71,12 @@
 #define EGL_CONTEXT_OPENGL_COMPATIBILITY_PROFILE_BIT_KHR 0x00000002
 #endif
 
+#ifndef EGL_IMG_context_priority
+#define EGL_CONTEXT_PRIORITY_LEVEL_IMG          0x3100
+#define EGL_CONTEXT_PRIORITY_HIGH_IMG           0x3101
+#define EGL_CONTEXT_PRIORITY_MEDIUM_IMG         0x3102
+#define EGL_CONTEXT_PRIORITY_LOW_IMG            0x3103
+#endif
 
 #define MAX_EGL_CONFIG_ATTRIBS 30
 
@@ -347,7 +353,7 @@ try_create_context (CoglDisplay *display,
   CoglRendererEGL *egl_renderer = renderer->winsys;
   EGLDisplay edpy;
   EGLConfig config;
-  EGLint attribs[9];
+  EGLint attribs[11];
   EGLint cfg_attribs[MAX_EGL_CONFIG_ATTRIBS];
   GError *config_error = NULL;
   const char *error_message;
@@ -404,6 +410,13 @@ try_create_context (CoglDisplay *display,
       attribs[i++] = 2;
     }
 
+  if (egl_renderer->private_features &
+      COGL_EGL_WINSYS_FEATURE_CONTEXT_PRIORITY)
+    {
+      attribs[i++] = EGL_CONTEXT_PRIORITY_LEVEL_IMG;
+      attribs[i++] = EGL_CONTEXT_PRIORITY_HIGH_IMG;
+    }
+
   attribs[i++] = EGL_NONE;
 
   egl_display->egl_context = eglCreateContext (edpy,
@@ -417,6 +430,20 @@ try_create_context (CoglDisplay *display,
       goto fail;
     }
 
+  if (egl_renderer->private_features &
+      COGL_EGL_WINSYS_FEATURE_CONTEXT_PRIORITY)
+    {
+      EGLint value = EGL_CONTEXT_PRIORITY_MEDIUM_IMG;
+
+      eglQueryContext (egl_renderer->edpy,
+                       egl_display->egl_context,
+                       EGL_CONTEXT_PRIORITY_LEVEL_IMG,
+                       &value);
+
+      if (value != EGL_CONTEXT_PRIORITY_HIGH_IMG)
+        g_warning ("Failed to obtain high priority context");
+    }
+
   if (egl_renderer->platform_vtable->context_created &&
       !egl_renderer->platform_vtable->context_created (display, error))
     return FALSE;