Add a GL 3 driver

This adds a new CoglDriver for GL 3 called COGL_DRIVER_GL3. When
requested, the GLX, EGL and SDL2 winsyss will set the necessary
attributes to request a forward-compatible core profile 3.1 context.
That means it will have no deprecated features.

To simplify the explosion of checks for specific combinations of
context->driver, many of these conditionals have now been replaced
with private feature flags that are checked instead. The GL and GLES
drivers now initialise these private feature flags depending on which
driver is used.

The fixed function backends now explicitly check whether the fixed
function private feature is available which means the GL3 driver will
fall back to always using the GLSL progend. Since Rob's latest patches
the GLSL progend no longer uses any fixed function API anyway so it
should just work.

The driver is currently lower priority than COGL_DRIVER_GL so it will
not be used unless it is specificly requested. We may want to change
this priority at some point because apparently Mesa can make some
memory savings if a core profile context is used.

In GL 3, getting the combined extensions string with glGetString is
deprecated so this patch changes it to use glGetStringi to build up an
array of extensions instead. _cogl_context_get_gl_extensions now
returns this array instead of trying to return a const string. The
caller is expected to free the array.

Some issues with this patch:

• GL 3 does not support GL_ALPHA format textures. We should probably
  make this a feature flag or something. Cogl uses this to render text
  which currently just throws a GL error and breaks so it's pretty
  important to do something about this before considering the GL3
  driver to be stable.

• GL 3 doesn't support client side vertex buffers. This probably
  doesn't matter because CoglBuffer won't normally use malloc'd
  buffers if VBOs are available, but it might but worth making
  malloc'd buffers a private feature and forcing it not to use them.

• GL 3 doesn't support the default vertex array object. This patch
  just makes it create and bind a single non-default vertex array
  object which gets used just like the normal default object. Ideally
  it would be good to use vertex array objects properly and attach
  them to a CoglPrimitive to cache the state.

Reviewed-by: Robert Bragg <robert@linux.intel.com>

(cherry picked from commit 66c9db993595b3a22e63f4c201ea468bc9b88cb6)

1 files changed, 48 insertions, 8 deletions

diff --git a/cogl/winsys/cogl-winsys-glx.c b/cogl/winsys/cogl-winsys-glx.c
index 6716c7c6..c9449ccf 100644
--- a/cogl/winsys/cogl-winsys-glx.c
+++ b/cogl/winsys/cogl-winsys-glx.c
@@ -331,7 +331,8 @@ _cogl_winsys_renderer_connect (CoglRenderer *renderer,
   if (!_cogl_xlib_renderer_connect (renderer, error))
     goto error;
 
-  if (renderer->driver != COGL_DRIVER_GL)
+  if (renderer->driver != COGL_DRIVER_GL &&
+      renderer->driver != COGL_DRIVER_GL3)
     {
       _cogl_set_error (error, COGL_WINSYS_ERROR,
                    COGL_WINSYS_ERROR_INIT,
@@ -394,6 +395,7 @@ update_winsys_features (CoglContext *context, CoglError **error)
     _cogl_xlib_renderer_get_data (context->display->renderer);
   CoglGLXRenderer *glx_renderer = context->display->renderer->winsys;
   const char *glx_extensions;
+  char **split_extensions;
   int default_screen;
   int i;
 
@@ -418,11 +420,13 @@ update_winsys_features (CoglContext *context, CoglError **error)
                   COGL_WINSYS_FEATURE_MULTIPLE_ONSCREEN,
                   TRUE);
 
+  split_extensions = g_strsplit (glx_extensions, " ", 0 /* max_tokens */);
+
   for (i = 0; i < G_N_ELEMENTS (winsys_feature_data); i++)
     if (_cogl_feature_check (context->display->renderer,
                              "GLX", winsys_feature_data + i, 0, 0,
                              COGL_DRIVER_GL, /* the driver isn't used */
-                             glx_extensions,
+                             split_extensions,
                              glx_renderer))
       {
         context->feature_flags |= winsys_feature_data[i].feature_flags;
@@ -432,6 +436,8 @@ update_winsys_features (CoglContext *context, CoglError **error)
                           TRUE);
       }
 
+  g_strfreev (split_extensions);
+
   /* Note: the GLX_SGI_video_sync spec explicitly states this extension
    * only works for direct contexts. */
   if (!glx_renderer->is_direct)
@@ -607,6 +613,36 @@ done:
   return ret;
 }
 
+static GLXContext
+create_gl3_context (CoglDisplay *display,
+                    GLXFBConfig fb_config)
+{
+  CoglXlibRenderer *xlib_renderer =
+    _cogl_xlib_renderer_get_data (display->renderer);
+  CoglGLXRenderer *glx_renderer = display->renderer->winsys;
+
+  /* We want a core profile 3.1 context with no deprecated features */
+  static const int attrib_list[] =
+    {
+      GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
+      GLX_CONTEXT_MINOR_VERSION_ARB, 1,
+      GLX_CONTEXT_PROFILE_MASK_ARB,  GLX_CONTEXT_CORE_PROFILE_BIT_ARB,
+      GLX_CONTEXT_FLAGS_ARB,         GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB,
+      None
+    };
+
+  /* Make sure that the display supports the GLX_ARB_create_context
+     extension */
+  if (glx_renderer->pf_glXCreateContextAttribs == NULL)
+    return NULL;
+
+  return glx_renderer->pf_glXCreateContextAttribs (xlib_renderer->xdpy,
+                                                   fb_config,
+                                                   NULL /* share_context */,
+                                                   True, /* direct */
+                                                   attrib_list);
+}
+
 static CoglBool
 create_context (CoglDisplay *display, CoglError **error)
 {
@@ -644,12 +680,16 @@ create_context (CoglDisplay *display, CoglError **error)
   COGL_NOTE (WINSYS, "Creating GLX Context (display: %p)",
              xlib_renderer->xdpy);
 
-  glx_display->glx_context =
-    glx_renderer->glXCreateNewContext (xlib_renderer->xdpy,
-                                       config,
-                                       GLX_RGBA_TYPE,
-                                       NULL,
-                                       True);
+  if (display->renderer->driver == COGL_DRIVER_GL3)
+    glx_display->glx_context = create_gl3_context (display, config);
+  else
+    glx_display->glx_context =
+      glx_renderer->glXCreateNewContext (xlib_renderer->xdpy,
+                                         config,
+                                         GLX_RGBA_TYPE,
+                                         NULL,
+                                         True);
+
   if (glx_display->glx_context == NULL)
     {
       _cogl_set_error (error, COGL_WINSYS_ERROR,