analysis: FALSE/0 used in pointer context

While this is totally fine (0 in the pointer context will be converted
in the right internal NULL representation, which could be a value with
some bits to 1), I believe it's clearer to use NULL in the pointer
context.

It seems that, in most case, it's more an overlook than a deliberate
choice to use FALSE/0 as NULL, eg. copying a _COGL_GET_CONTEXT (ctx, 0)
or a g_return_val_if_fail (cond, 0) from a function returning a
gboolean.

cogl/cogl-buffer.c

@@ -236,7 +236,7 @@ cogl_buffer_map_EXP (CoglBuffer      *buffer,
                      CoglBufferAccess access)
 {
   if (!cogl_is_buffer (buffer))
-    return FALSE;
+    return NULL;
 
   if (COGL_BUFFER_FLAG_IS_SET (buffer, MAPPED))
     return buffer->data;

cogl/cogl-journal.c

@@ -537,7 +537,7 @@ upload_vertices_to_vbo (GArray *vertices, CoglJournalFlushState *state)
 
   /* As we flush the journal entries in batches we walk forward through the
    * above VBO starting at offset 0... */
-  state->vbo_offset = 0;
+  state->vbo_offset = NULL;
 
   return journal_vbo;
 }

cogl/cogl-path.c

@@ -1065,7 +1065,7 @@ cogl_path_rel_curve_to (float x_1,
 CoglHandle
 cogl_path_get (void)
 {
-  _COGL_GET_CONTEXT (ctx, FALSE);
+  _COGL_GET_CONTEXT (ctx, NULL);
 
   return ctx->current_path;
 }
@@ -1106,7 +1106,7 @@ cogl_path_copy (CoglHandle handle)
 {
   CoglPath *old_path, *new_path;
 
-  _COGL_GET_CONTEXT (ctx, FALSE);
+  _COGL_GET_CONTEXT (ctx, NULL);
 
   if (!cogl_is_path (handle))
     return COGL_INVALID_HANDLE;

cogl/cogl-texture-2d-sliced.c

@@ -864,7 +864,7 @@ _cogl_texture_2d_sliced_slices_create (CoglTexture2DSliced *tex_2ds,
           /* Pass NULL data to init size and internal format */
           GE( glTexImage2D (tex_2ds->gl_target, 0, gl_intformat,
                             x_span->size, y_span->size, 0,
-                            gl_format, gl_type, 0) );
+                            gl_format, gl_type, NULL) );
         }
     }
 

cogl/cogl-vertex-buffer.c

@@ -800,7 +800,7 @@ filter_strided_attribute (CoglVertexBufferAttrib *attribute,
 	}
     }
   new_cogl_vbo = g_slice_alloc (sizeof (CoglVertexBufferVBO));
-  new_cogl_vbo->vbo_name = 0;
+  new_cogl_vbo->vbo_name = NULL;
   new_cogl_vbo->attributes = NULL;
   new_cogl_vbo->attributes =
     g_list_prepend (new_cogl_vbo->attributes, attribute);
@@ -1059,7 +1059,7 @@ upload_gl_vbo (CoglVertexBufferVBO *cogl_vbo)
 
   if (!fallback)
     {
-      g_return_if_fail (cogl_vbo->vbo_name != 0);
+      g_return_if_fail (cogl_vbo->vbo_name != NULL);
 
       GE (glBindBuffer (GL_ARRAY_BUFFER,
 			GPOINTER_TO_UINT (cogl_vbo->vbo_name)));
@@ -1352,7 +1352,7 @@ cogl_vertex_buffer_submit_real (CoglVertexBuffer *buffer)
    */
 
   new_multipack_vbo = g_slice_alloc (sizeof (CoglVertexBufferVBO));
-  new_multipack_vbo->vbo_name = 0;
+  new_multipack_vbo->vbo_name = NULL;
   new_multipack_vbo->flags =
     COGL_VERTEX_BUFFER_VBO_FLAG_MULTIPACK
     | COGL_VERTEX_BUFFER_VBO_FLAG_INFREQUENT_RESUBMIT;
@@ -1400,7 +1400,7 @@ cogl_vertex_buffer_submit_real (CoglVertexBuffer *buffer)
 	   * in their own VBO so that updates don't impact other attributes
 	   */
 
-	  cogl_vbo->vbo_name = 0;
+	  cogl_vbo->vbo_name = NULL;
 	  cogl_vbo->flags =
             COGL_VERTEX_BUFFER_VBO_FLAG_UNSTRIDED
 	    | COGL_VERTEX_BUFFER_VBO_FLAG_FREQUENT_RESUBMIT;
@@ -1546,7 +1546,7 @@ enable_state_for_drawing_buffer (CoglVertexBuffer *buffer)
 	{
 	  GE (glBindBuffer (GL_ARRAY_BUFFER,
 			    GPOINTER_TO_UINT (cogl_vbo->vbo_name)));
-	  base = 0;
+	  base = NULL;
 	}
       else
 	base = cogl_vbo->vbo_name;
@@ -1832,7 +1832,7 @@ cogl_vertex_buffer_indices_new (CoglIndicesType  indices_type,
   gsize indices_bytes;
   CoglVertexBufferIndices *indices;
 
-  _COGL_GET_CONTEXT (ctx, 0);
+  _COGL_GET_CONTEXT (ctx, NULL);
 
   indices = g_slice_alloc (sizeof (CoglVertexBufferIndices));
 
@@ -1852,7 +1852,7 @@ cogl_vertex_buffer_indices_new (CoglIndicesType  indices_type,
     {
       g_critical ("unknown indices type %d", indices_type);
       g_slice_free (CoglVertexBufferIndices, indices);
-      return 0;
+      return NULL;
     }
 
   indices_bytes = get_indices_type_size (indices->type) * indices_len;

cogl/driver/gl/cogl-program.c

@@ -78,7 +78,7 @@ CoglHandle
 cogl_create_program (void)
 {
   CoglProgram *program;
-  _COGL_GET_CONTEXT (ctx, 0);
+  _COGL_GET_CONTEXT (ctx, NULL);
 
   program = g_slice_new (CoglProgram);
   program->gl_handle = glCreateProgramObject ();