[paint] Add API for custom palettes

src/hb-paint.cc

@@ -117,6 +117,11 @@ hb_paint_pop_group_nil (hb_paint_funcs_t *funcs, void *paint_data,
                         hb_paint_composite_mode_t mode,
                         void *user_data) {}
 
+static hb_color_t
+hb_paint_custom_palette_color_nil (hb_paint_funcs_t *funcs, void *paint_data,
+                                   unsigned int color_index,
+                                   void *user_data) { return HB_COLOR(0,0,0,0); }
+
 static bool
 _hb_paint_funcs_set_preamble (hb_paint_funcs_t  *funcs,
                              bool                func_is_null,
@@ -673,5 +678,23 @@ hb_paint_pop_group (hb_paint_funcs_t *funcs, void *paint_data,
   funcs->pop_group (paint_data, mode);
 }
 
+/**
+ * hb_paint_custom_palette_color:
+ * @funcs: paint functions
+ * @paint_data: associated data passed by the caller
+ * @color_index: color index
+ *
+ * Gets the custom palette color for @color_index.
+ *
+ * Return value: the custom color
+ *
+ * Since: REPLACEME
+ */
+hb_color_t
+hb_paint_custom_palette_color (hb_paint_funcs_t *funcs, void *paint_data,
+                               unsigned int color_index)
+{
+  return funcs->custom_palette_color (paint_data, color_index);
+}
 
 #endif

src/hb-paint.h

@@ -655,6 +655,25 @@ typedef void (*hb_paint_pop_group_func_t) (hb_paint_funcs_t *funcs,
                                            hb_paint_composite_mode_t mode,
                                            void *user_data);
 
+/**
+ * hb_paint_custom_palette_color_func_t:
+ * @funcs: paint functions object
+ * @paint_data: The data accompanying the paint functions in hb_font_paint_glyph()
+ * @color_index: the color index
+ * @user_data: User data pointer passed to hb_paint_funcs_set_pop_group_func()
+ *
+ * A virtual method for the #hb_paint_funcs_t to fetch a color from the custom
+ * color palette.
+ *
+ * Return value: the color
+ * Since: REPLACEME
+ */
+typedef hb_color_t (*hb_paint_custom_palette_color_func_t) (hb_paint_funcs_t *funcs,
+                                                            void *paint_data,
+                                                            unsigned int color_index,
+                                                            void *user_data);
+
+
 /**
  * hb_paint_funcs_set_push_transform_func:
  * @funcs: A paint functions struct
@@ -859,6 +878,22 @@ hb_paint_funcs_set_pop_group_func (hb_paint_funcs_t          *funcs,
                                    void                       *user_data,
                                    hb_destroy_func_t           destroy);
 
+/**
+ * hb_paint_funcs_set_custom_palette_color_func:
+ * @funcs: A paint functions struct
+ * @func: (closure user_data) (destroy destroy) (scope notified): The get-custom-palette-color callback
+ * @user_data: Data to pass to @func
+ * @destroy: (nullable): Function to call when @user_data is no longer needed
+ *
+ * Sets the get-custom-paletter-color callback on the paint functions struct.
+ *
+ * Since: REPLACEME
+ */
+HB_EXTERN void
+hb_paint_funcs_set_custom_palette_color_func (hb_paint_funcs_t                     *funcs,
+                                              hb_paint_custom_palette_color_func_t  func,
+                                              void                                 *user_data,
+                                              hb_destroy_func_t                     destroy);
 /*
  * Manual API
  */
@@ -927,6 +962,10 @@ HB_EXTERN void
 hb_paint_pop_group (hb_paint_funcs_t *funcs, void *paint_data,
                     hb_paint_composite_mode_t mode);
 
+HB_EXTERN hb_color_t
+hb_paint_custom_palette_color (hb_paint_funcs_t *funcs, void *paint_data,
+                               unsigned int color_index);
+
 HB_END_DECLS
 
 #endif  /* HB_PAINT_H */

src/hb-paint.hh

@@ -42,6 +42,7 @@
   HB_PAINT_FUNC_IMPLEMENT (sweep_gradient) \
   HB_PAINT_FUNC_IMPLEMENT (push_group) \
   HB_PAINT_FUNC_IMPLEMENT (pop_group) \
+  HB_PAINT_FUNC_IMPLEMENT (custom_palette_color) \
   /* ^--- Add new callbacks here */
 
 struct hb_paint_funcs_t
@@ -137,6 +138,11 @@ struct hb_paint_funcs_t
   { func.pop_group (this, paint_data,
                     mode,
                     !user_data ? nullptr : user_data->pop_group); }
+  hb_color_t custom_palette_color (void *paint_data,
+                             unsigned int color_index)
+  { return func.custom_palette_color (this, paint_data,
+                                      color_index,
+                                      !user_data ? nullptr : user_data->custom_palette_color); }
 
 
   /* Internal specializations. */