[draw] Clarify the docs

Disambiguate the origin of draw_data and user_data,
this had me confused a few times.

Fixes: https://github.com/harfbuzz/harfbuzz/issues/3955

src/hb-draw.h

@@ -92,11 +92,11 @@ typedef struct hb_draw_funcs_t hb_draw_funcs_t;
 /**
  * hb_draw_move_to_func_t:
  * @dfuncs: draw functions object
- * @draw_data: The data accompanying the draw functions
+ * @draw_data: The data accompanying the draw functions in hb_font_get_glyph_shape()
  * @st: current draw state
  * @to_x: X component of target point
  * @to_y: Y component of target point
- * @user_data: User data pointer passed by the caller
+ * @user_data: User data pointer passed to hb_draw_funcs_set_move_to_func()
  *
  * A virtual method for the #hb_draw_funcs_t to perform a "move-to" draw
  * operation.
@@ -112,11 +112,11 @@ typedef void (*hb_draw_move_to_func_t) (hb_draw_funcs_t *dfuncs, void *draw_data
 /**
  * hb_draw_line_to_func_t:
  * @dfuncs: draw functions object
- * @draw_data: The data accompanying the draw functions
+ * @draw_data: The data accompanying the draw functions in hb_font_get_glyph_shape()
  * @st: current draw state
  * @to_x: X component of target point
  * @to_y: Y component of target point
- * @user_data: User data pointer passed by the caller
+ * @user_data: User data pointer passed to hb_draw_funcs_set_line_to_func()
  *
  * A virtual method for the #hb_draw_funcs_t to perform a "line-to" draw
  * operation.
@@ -132,13 +132,13 @@ typedef void (*hb_draw_line_to_func_t) (hb_draw_funcs_t *dfuncs, void *draw_data
 /**
  * hb_draw_quadratic_to_func_t:
  * @dfuncs: draw functions object
- * @draw_data: The data accompanying the draw functions
+ * @draw_data: The data accompanying the draw functions in hb_font_get_glyph_shape()
  * @st: current draw state
  * @control_x: X component of control point
  * @control_y: Y component of control point
  * @to_x: X component of target point
  * @to_y: Y component of target point
- * @user_data: User data pointer passed by the caller
+ * @user_data: User data pointer passed to hb_draw_funcs_set_quadratic_to_func()
  *
  * A virtual method for the #hb_draw_funcs_t to perform a "quadratic-to" draw
  * operation.
@@ -155,7 +155,7 @@ typedef void (*hb_draw_quadratic_to_func_t) (hb_draw_funcs_t *dfuncs, void *draw
 /**
  * hb_draw_cubic_to_func_t:
  * @dfuncs: draw functions object
- * @draw_data: The data accompanying the draw functions
+ * @draw_data: The data accompanying the draw functions in hb_font_get_glyph_shape()
  * @st: current draw state
  * @control1_x: X component of first control point
  * @control1_y: Y component of first control point
@@ -163,7 +163,7 @@ typedef void (*hb_draw_quadratic_to_func_t) (hb_draw_funcs_t *dfuncs, void *draw
  * @control2_y: Y component of second control point
  * @to_x: X component of target point
  * @to_y: Y component of target point
- * @user_data: User data pointer passed by the caller
+ * @user_data: User data pointer passed to hb_draw_funcs_set_cubic_to_func()
  *
  * A virtual method for the #hb_draw_funcs_t to perform a "cubic-to" draw
  * operation.
@@ -181,9 +181,9 @@ typedef void (*hb_draw_cubic_to_func_t) (hb_draw_funcs_t *dfuncs, void *draw_dat
 /**
  * hb_draw_close_path_func_t:
  * @dfuncs: draw functions object
- * @draw_data: The data accompanying the draw functions
+ * @draw_data: The data accompanying the draw functions in hb_font_get_glyph_shape()
  * @st: current draw state
- * @user_data: User data pointer passed by the caller
+ * @user_data: User data pointer passed to hb_draw_funcs_Set_close_path_func()
  *
  * A virtual method for the #hb_draw_funcs_t to perform a "close-path" draw
  * operation.