[gtk+] gdk/gl: Allow autodetection for GL/GLES

[Matthias Clasen <matthiasc src gnome org>]

commit b878ec7f2ff51d4a38bb70f2461bcf1344608dcb
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Oct 19 13:43:17 2016 +0100

    gdk/gl: Allow autodetection for GL/GLES
    
    If the GdkGLContext was not explicitly instructed to use or not GLES, we
    can detect whether the underlying API is going to be desktop GL or GLES.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=773180

 gdk/gdkglcontext.c |   26 +++++++++++++++++++++-----
 gdk/gdkglcontext.h |    2 +-
 2 files changed, 22 insertions(+), 6 deletions(-)
---
diff --git a/gdk/gdkglcontext.c b/gdk/gdkglcontext.c
index 216a19a..248ce11 100644
--- a/gdk/gdkglcontext.c
+++ b/gdk/gdkglcontext.c
@@ -105,7 +105,8 @@ typedef struct {
   guint debug_enabled : 1;
   guint forward_compatible : 1;
   guint is_legacy : 1;
-  guint use_es : 1;
+
+  int use_es;
 
   GdkGLContextPaintData *paint_data;
 } GdkGLContextPrivate;
@@ -362,6 +363,9 @@ gdk_gl_context_class_init (GdkGLContextClass *klass)
 static void
 gdk_gl_context_init (GdkGLContext *self)
 {
+  GdkGLContextPrivate *priv = gdk_gl_context_get_instance_private (self);
+
+  priv->use_es = -1;
 }
 
 /*< private >
@@ -683,13 +687,18 @@ gdk_gl_context_set_is_legacy (GdkGLContext *context,
 /**
  * gdk_gl_context_set_use_es:
  * @context: a #GdkGLContext:
- * @use_es: whether the context should use OpenGL ES instead of OpenGL
+ * @use_es: whether the context should use OpenGL ES instead of OpenGL,
+ *   or -1 to allow auto-detection
  *
  * Requests that GDK create a OpenGL ES context instead of an OpenGL one,
  * if the platform and windowing system allows it.
  *
  * The @context must not have been realized.
  *
+ * By default, GDK will attempt to automatically detect whether the
+ * underlying GL implementation is OpenGL or OpenGL ES once the @context
+ * is realized.
+ *
  * You should check the return value of gdk_gl_context_get_use_es() after
  * calling gdk_gl_context_realize() to decide whether to use the OpenGL or
  * OpenGL ES API, extensions, or shaders.
@@ -698,14 +707,15 @@ gdk_gl_context_set_is_legacy (GdkGLContext *context,
  */
 void
 gdk_gl_context_set_use_es (GdkGLContext *context,
-                           gboolean      use_es)
+                           int           use_es)
 {
   GdkGLContextPrivate *priv = gdk_gl_context_get_instance_private (context);
 
   g_return_if_fail (GDK_IS_GL_CONTEXT (context));
   g_return_if_fail (!priv->realized);
 
-  priv->use_es = !!use_es;
+  if (priv->use_es != use_es)
+    priv->use_es = use_es;
 }
 
 /**
@@ -725,7 +735,10 @@ gdk_gl_context_get_use_es (GdkGLContext *context)
 
   g_return_val_if_fail (GDK_IS_GL_CONTEXT (context), FALSE);
 
-  return priv->use_es;
+  if (!priv->realized)
+    return FALSE;
+
+  return priv->use_es > 0;
 }
 
 /**
@@ -771,6 +784,9 @@ gdk_gl_context_check_extensions (GdkGLContext *context)
 
   priv->gl_version = epoxy_gl_version ();
 
+  if (priv->use_es < 0)
+    priv->use_es = !epoxy_is_desktop_gl ();
+
   if (priv->use_es)
     {
       has_npot = priv->gl_version >= 20;
diff --git a/gdk/gdkglcontext.h b/gdk/gdkglcontext.h
index 44633a7..eb380c2 100644
--- a/gdk/gdkglcontext.h
+++ b/gdk/gdkglcontext.h
@@ -75,7 +75,7 @@ GDK_AVAILABLE_IN_3_16
 gboolean                gdk_gl_context_get_forward_compatible   (GdkGLContext  *context);
 GDK_AVAILABLE_IN_3_22
 void                    gdk_gl_context_set_use_es               (GdkGLContext  *context,
-                                                                 gboolean       use_es);
+                                                                 int            use_es);
 GDK_AVAILABLE_IN_3_22
 gboolean                gdk_gl_context_get_use_es               (GdkGLContext  *context);