Validate that the GL version is >= 1.2

There is a new internal Cogl function called _cogl_check_driver_valid
which looks at the value of the GL_VERSION string to determine whether
the driver is supported. Clutter now calls this after the stage is
realized. If it fails then the stage is marked as unrealized and a
warning is shown.

_cogl_features_init now also checks the version number before getting
the function pointers for glBlendFuncSeparate and
glBlendEquationSeparate. It is not safe to just check for the presence
of the functions because some drivers may define the function without
fully implementing the spec.

The GLES version of _cogl_check_driver_valid just always returns TRUE
because there are no version requirements yet.

Eventually the function could also check for mandatory extensions if
there were any.

http://bugzilla.openedhand.com/show_bug.cgi?id=1875

cogl/cogl.c

@@ -942,3 +942,8 @@ _cogl_get_clip_state (void)
   return _cogl_draw_buffer_get_clip_state (draw_buffer);
 }
 
+GQuark
+_cogl_driver_error_quark (void)
+{
+  return g_quark_from_static_string ("cogl-driver-error-quark");
+}

cogl/cogl.h.in

@@ -969,8 +969,17 @@ void            cogl_flush_gl_state         (int      flags);
 #endif
 
 /* private */
+#define COGL_DRIVER_ERROR (_cogl_driver_error_quark ())
+
+typedef enum { /*< prefix=COGL_DRIVER_ERROR >*/
+  COGL_DRIVER_ERROR_UNKNOWN_VERSION,
+  COGL_DRIVER_ERROR_INVALID_VERSION
+} CoglDriverError;
+
 void            _cogl_set_indirect_context  (gboolean indirect);
 void            _cogl_set_viewport (int x, int y, int width, int height);
+gboolean        _cogl_check_driver_valid (GError **error);
+GQuark          _cogl_driver_error_quark (void);
 
 void
 _cogl_onscreen_clutter_backend_set_size (int width, int height);

cogl/driver/gl/cogl.c

@@ -32,6 +32,11 @@
 #include "cogl-internal.h"
 #include "cogl-context.h"
 
+#define COGL_CHECK_GL_VERSION(driver_major, driver_minor, \
+                              target_major, target_minor) \
+  ((driver_major) > (target_major) || \
+   ((driver_major) == (target_major) && (driver_minor) >= (target_minor)))
+
 typedef struct _CoglGLSymbolTableEntry
 {
   const char *name;
@@ -109,6 +114,70 @@ really_enable_npot (void)
 }
 #endif
 
+static gboolean
+_cogl_get_gl_version (int *major_out, int *minor_out)
+{
+  const char *version_string, *major_end, *minor_end;
+  int major = 0, minor = 0;
+
+  /* Get the OpenGL version number */
+  if ((version_string = (const char *) glGetString (GL_VERSION)) == NULL)
+    return FALSE;
+
+  /* Extract the major number */
+  for (major_end = version_string; *major_end >= '0'
+	 && *major_end <= '9'; major_end++)
+    major = (major * 10) + *major_end - '0';
+  /* If there were no digits or the major number isn't followed by a
+     dot then it is invalid */
+  if (major_end == version_string || *major_end != '.')
+    return FALSE;
+
+  /* Extract the minor number */
+  for (minor_end = major_end + 1; *minor_end >= '0'
+	 && *minor_end <= '9'; minor_end++)
+    minor = (minor * 10) + *minor_end - '0';
+  /* If there were no digits or there is an unexpected character then
+     it is invalid */
+  if (minor_end == major_end + 1
+      || (*minor_end && *minor_end != ' ' && *minor_end != '.'))
+    return FALSE;
+
+  *major_out = major;
+  *minor_out = minor;
+
+  return TRUE;
+}
+
+gboolean
+_cogl_check_driver_valid (GError **error)
+{
+  int major, minor;
+
+  if (!_cogl_get_gl_version (&major, &minor))
+    {
+      g_set_error (error,
+                   COGL_DRIVER_ERROR,
+                   COGL_DRIVER_ERROR_UNKNOWN_VERSION,
+                   "The OpenGL version could not be determined");
+      return FALSE;
+    }
+
+  /* OpenGL 1.2 is required */
+  if (!COGL_CHECK_GL_VERSION (major, minor, 1, 2))
+    {
+      g_set_error (error,
+                   COGL_DRIVER_ERROR,
+                   COGL_DRIVER_ERROR_INVALID_VERSION,
+                   "The OpenGL version of your driver (%i.%i) "
+                   "is not compatible with Cogl",
+                   major, minor);
+      return FALSE;
+    }
+
+  return TRUE;
+}
+
 void
 _cogl_features_init (void)
 {
@@ -119,9 +188,12 @@ _cogl_features_init (void)
   gboolean          fbo_ARB = FALSE;
   gboolean          fbo_EXT = FALSE;
   const char       *suffix;
+  int               gl_major = 0, gl_minor = 0;
 
   _COGL_GET_CONTEXT (ctx, NO_RETVAL);
 
+  _cogl_get_gl_version (&gl_major, &gl_minor);
+
   flags = COGL_FEATURE_TEXTURE_READ_PIXELS;
 
   gl_extensions = (const gchar*) glGetString (GL_EXTENSIONS);
@@ -427,11 +499,13 @@ _cogl_features_init (void)
          cogl_get_proc_address ("glBlendColor");
 
   /* Available in 1.4 */
+  if (COGL_CHECK_GL_VERSION (gl_major, gl_minor, 1, 4))
     ctx->drv.pf_glBlendFuncSeparate =
       (COGL_PFNGLBLENDFUNCSEPARATEPROC)
       cogl_get_proc_address ("glBlendFuncSeparate");
 
   /* Available in 2.0 */
+  if (COGL_CHECK_GL_VERSION (gl_major, gl_minor, 2, 0))
     ctx->drv.pf_glBlendEquationSeparate =
       (COGL_PFNGLBLENDEQUATIONSEPARATEPROC)
       cogl_get_proc_address ("glBlendEquationSeparate");
@@ -440,4 +514,3 @@ _cogl_features_init (void)
   ctx->feature_flags = flags;
   ctx->features_cached = TRUE;
 }
-

cogl/driver/gles/cogl.c

@@ -82,6 +82,12 @@ _cogl_resolve_gl_symbols (CoglGLSymbolTableEntry *symbol_table,
   return status;
 }
 
+gboolean
+_cogl_check_driver_valid (GError **error)
+{
+  /* The GLES backend doesn't have any particular version requirements */
+  return TRUE;
+}
 
 void
 _cogl_features_init (void)