LVGL v8 arctext (curvetext)

SiFli SDK provides arc text (Arc Text) display capability on LVGL v8, with the corresponding SDK header lvsf_curvetext.h (widget class name lvsfcurve). Built on top of lv_canvas, it draws characters arranged along an arc, supports setting the text angle and radius along the arc, and can draw an arc background line. It is commonly used for arc text layout scenarios such as watch-face edges and ring-menu titles.

Note

The lv_arctext_* interfaces used in the solution document differ in naming from the lv_lvsfcurve_* interfaces in the current SDK v8 header lvsf_curvetext.h. The API table in this document follows the SDK header; the alignment, equal-spacing, mirroring, and other feature descriptions related to lv_arctext_* can serve as a design reference.

Features

Draws text arranged along an arc, with a configurable start angle and radius.
Supports drawing an arc background line (radius, start/end angle, color, line width).
Supports setting the rotation pivot point.
Depends on the LVGL canvas (LV_USE_CANVAS) as the drawing backend.

Use Cases

Text wrapping around the outer edge of a watch face.
Title text along the edge of a ring menu / circular widget.
Interfaces that require text arranged along an arc together with arc scale lines.

Supported Boards

Any platform supported by the general LVGL v8 examples, and any board from 55x onward (such as 58x, 56x, 52x). Enable LV_USE_CANVAS in lv_conf.h and LVSF_USE_CURVE in menuconfig.

Configuration and Initialization

Arc text depends on the LVGL canvas, which must first be enabled in lv_conf.h:

LV_USE_CANVAS  1

Then enable LVSF_USE_CURVE under LittlevGL2RTT -> SiFli extend in menuconfig.

#include "lvsf/lvsf_curvetext.h"

API Reference

The interface signatures below are taken verbatim from middleware/lvgl/lvsf/lvsf_curvetext.h:

Function	Description	Parameters / Returns
`lv_obj_t lv_lvsfcurve_create(lv_obj_t parent)`	Create an arc text (curve) object	`parent`: parent object; returns the created object pointer
`void lv_lvsfcurve_set_buf(lv_obj_t *curve, uint16_t txt_width, uint16_t txt_height)`	Set the arc text drawing buffer size	`txt_width`/`txt_height`: text area width and height (pixels)
`void lv_lvsfcurve_set_pivot(lv_obj_t *curve, lv_coord_t x, lv_coord_t y)`	Set the rotation pivot point	`x`/`y`: pivot coordinates
`void lv_lvsfcurve_draw_arc(lv_obj_t *curve, lv_coord_t r, int32_t start_angle, int32_t end_angle, lv_color_t color, lv_coord_t width)`	Draw an arc background line	`r`: radius; `start_angle`/`end_angle`: start/end angles; `color`: color; `width`: line width
`void lv_lvsfcurve_text(lv_obj_t curve, char text, int angle, int r, lv_color_t color, int size)`	Draw text along the arc	`text`: text to display; `angle`: start angle; `r`: radius; `color`: color; `size`: font size

Typical Usage

Create an arc text object, set the buffer and pivot point, then draw the text along the arc and an arc line:

lv_obj_t *arc = lv_lvsfcurve_create(parent);
lv_obj_set_size(arc, LV_HOR_RES_MAX >> 1, LV_HOR_RES_MAX >> 1);
lv_obj_center(arc);

/* Set the drawing buffer and rotation pivot */
lv_lvsfcurve_set_buf(arc, LV_HOR_RES_MAX >> 1, LV_HOR_RES_MAX >> 1);
lv_lvsfcurve_set_pivot(arc, LV_HOR_RES_MAX >> 2, LV_HOR_RES_MAX >> 2);

/* Draw text along the arc: start from the 0-degree direction, radius 80, white */
lv_lvsfcurve_text(arc, "ARCTEXT", 0, 80, LV_COLOR_WHITE, 20);

/* Draw an arc background line */
lv_lvsfcurve_draw_arc(arc, 80, 0, 360, LV_COLOR_BLUE, 2);