lcd/skin_engine: Add the ability to draw onto the backdrop layer

The framebuffer the lcd driver uses can now be changed on the fly
which means that regular lcd_* drawing functions can draw onto the
"backdrop" buffer. The skin engine can use this to create layered
effects.

Add the tag %VB to a viewport to draw that viewport onto the
backdrop layer. If you want to draw an image onto the backdrop
framebuffer use %x(backdrop filename) instead of %X() inside
a viewport with %VB.

Change-Id: I741498e2af6d4f2d78932cabe8942317893e7cfc

1 files changed, 3 insertions, 0 deletions

diff --git a/apps/screen_access.h b/apps/screen_access.h
index a9d1408898..343829b915 100644
--- a/apps/screen_access.h
+++ b/apps/screen_access.h
@@ -160,6 +160,9 @@ struct screen
     bool (*backdrop_load)(const char *filename, char* backdrop_buffer);
     void (*backdrop_show)(char* backdrop_buffer);
 #endif
+#if defined(HAVE_LCD_BITMAP)
+    void (*set_framebuffer)(void *framebuffer);
+#endif
 };
 
 #if defined(HAVE_LCD_BITMAP) || defined(HAVE_REMOTE_LCD)