UI: ShaderFx Drag and Drop, Layout Updates

This patch implements the list panel system D7490 for grease pencil
shader effects. It also moves their drawing to a callback in
ShaderFxTypeInfo in line with the extensible architecture refactoring
goal T75724.

The implementation is basically exactly the same as for the modifier
patch (9b099c8612).

Thanks to Matias Mendiola (@mendio) for helping to develop the layout
changes.

Differential Revision: https://developer.blender.org/D7985

source/blender/shader_fx/intern/FX_ui_common.h

@@ -0,0 +1,56 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup modifiers
+ */
+
+#ifndef __FX_UI_COMMON_H__
+#define __FX_UI_COMMON_H__
+
+#include "FX_shader_types.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct ARegionType;
+struct bContext;
+struct PanelType;
+struct uiLayout;
+typedef void (*PanelDrawFn)(const bContext *, Panel *);
+
+void shaderfx_panel_end(struct uiLayout *layout, PointerRNA *ptr);
+
+void shaderfx_panel_get_property_pointers(const bContext *C,
+                                          struct Panel *panel,
+                                          struct PointerRNA *r_ob_ptr,
+                                          struct PointerRNA *r_ptr);
+
+PanelType *shaderfx_panel_register(ARegionType *region_type, ShaderFxType type, PanelDrawFn draw);
+
+struct PanelType *shaderfx_subpanel_register(struct ARegionType *region_type,
+                                             const char *name,
+                                             const char *label,
+                                             PanelDrawFn draw_header,
+                                             PanelDrawFn draw,
+                                             struct PanelType *parent);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __FX_UI_COMMON_H__ */