add arc drawing and restructure draw functions

lv_draw/lv_draw_arc.h

@@ -0,0 +1,52 @@
+/**
+ * @file lv_draw_arc.h
+ *
+ */
+
+#ifndef LV_DRAW_ARC_H
+#define LV_DRAW_ARC_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*********************
+ *      INCLUDES
+ *********************/
+#include "lv_draw.h"
+
+/*********************
+ *      DEFINES
+ *********************/
+
+/**********************
+ *      TYPEDEFS
+ **********************/
+
+/**********************
+ * GLOBAL PROTOTYPES
+ **********************/
+
+/**
+ * Draw an arc. (Can draw pie too with great thickness.)
+ * @param center_x the x coordinate of the center of the arc
+ * @param center_y the y coordinate of the center of the arc
+ * @param mask the arc will be drawn only in this mask
+ * @param radius the radius of the arc
+ * @param start_angle the start angle of the arc (0 deg on the bottom, 90 deg on the right)
+ * @param end_angle the end angle of the arc
+ * @param thickness the thickness of the arc (set the `radius` to draw pie)
+ */
+void lv_draw_arc(lv_coord_t center_x, lv_coord_t center_y, const lv_area_t * mask, uint16_t radius,
+		         uint16_t start_angle, uint16_t end_angle, uint16_t tickness);
+
+/**********************
+ *      MACROS
+ **********************/
+
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /*LV_DRAW_ARC*/