pipeline-arbfp: Check for fog on the pipeline not the legacy state

The ARBfp backend can't handle fog so it tries to check for when it's
enabled and bails out. However it was checking using the global legacy
state value on the CoglContext but this doesn't necessarily reflect
the state that will actually be used by the pipeline because Cogl may
have internally pushed a different pipeline.

This patch adds an internal _cogl_pipeline_get_fog_enabled which the
ARBfp backend now uses.

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

cogl/cogl-pipeline-fragend-arbfp.c

@@ -165,7 +165,7 @@ _cogl_pipeline_fragend_arbfp_start (CoglPipeline *pipeline,
     return FALSE;
 
   /* TODO: support fog */
-  if (ctx->legacy_fog_state.enabled)
+  if (_cogl_pipeline_get_fog_enabled (pipeline))
     return FALSE;
 
   user_program = cogl_pipeline_get_user_program (pipeline);

cogl/cogl-pipeline-private.h

@@ -1184,6 +1184,9 @@ void
 _cogl_pipeline_set_blend_enabled (CoglPipeline *pipeline,
                                   CoglPipelineBlendEnable enable);
 
+gboolean
+_cogl_pipeline_get_fog_enabled (CoglPipeline *pipeline);
+
 void
 _cogl_pipeline_set_static_breadcrumb (CoglPipeline *pipeline,
                                       const char *breadcrumb);

cogl/cogl-pipeline.c

@@ -2855,6 +2855,18 @@ _cogl_pipeline_update_authority (CoglPipeline *pipeline,
     }
 }
 
+gboolean
+_cogl_pipeline_get_fog_enabled (CoglPipeline *pipeline)
+{
+  CoglPipeline *authority;
+
+  g_return_val_if_fail (cogl_is_pipeline (pipeline), FALSE);
+
+  authority =
+    _cogl_pipeline_get_authority (pipeline, COGL_PIPELINE_STATE_FOG);
+  return authority->big_state->fog_state.enabled;
+}
+
 unsigned long
 _cogl_pipeline_get_age (CoglPipeline *pipeline)
 {