transparent canvas with chroma keying for little vGL

• 定义画布尺寸

  #define TRANSPARENT_CANVAS_WIDTH    50
  #define TRANSPARENT_CANVAS_HIGHT    50

• 创建一个button

  lv_btn_create(lv_scr_act(), NULL);

• 定义画布缓冲buffer，注意不能是局部的

  static lv_color_t cbuf[LV_CANVAS_BUF_SIZE_INDEXED_1BIT(TRANSPARENT_CANVAS_WIDTH,
      TRANSPARENT_CANVAS_HIGHT)];

• 创建画布对象

   lv_obj_t* canvas = lv_canvas_create(lv_scr_act(), NULL);

• 设置关联画布缓冲buffer

   lv_canvas_set_buffer(canvas, cbuf, TRANSPARENT_CANVAS_WIDTH, TRANSPARENT_CANVAS_HIGHT, LV_IMG_CF_INDEXED_1BIT);
     

•    设置透明和红色2个调色盘

      lv_canvas_set_palette(canvas, 0, LV_COLOR_TRANSP);
      lv_canvas_set_palette(canvas, 1, LV_COLOR_RED);

• 定义颜色变量C0,C1

      lv_color_t c0;
      lv_color_t c1;
      c0.full = 0;
      c1.full = 1;
  

• 绘制C0,C1

    lv_canvas_fill_bg(canvas, c1);
    uint32_t x, y;
    for (y = 10; y < 30; y++)
    {
        for (x = 5; x < 20; x++)
        {
            lv_canvas_set_px(canvas, x, y, c0);
        }
    }

• 完整的实现

#define TRANSPARENT_CANVAS_WIDTH    50
#define TRANSPARENT_CANVAS_HIGHT    50
void transparent_canvas_demo(void) {
    lv_btn_create(lv_scr_act(), NULL);
    static lv_color_t cbuf[LV_CANVAS_BUF_SIZE_INDEXED_1BIT(TRANSPARENT_CANVAS_WIDTH,
    TRANSPARENT_CANVAS_HIGHT)];

    lv_obj_t* canvas = lv_canvas_create(lv_scr_act(), NULL);
    lv_canvas_set_buffer(canvas, cbuf, TRANSPARENT_CANVAS_WIDTH, TRANSPARENT_CANVAS_HIGHT, LV_IMG_CF_INDEXED_1BIT);
    lv_canvas_set_palette(canvas, 0, LV_COLOR_TRANSP);
    lv_canvas_set_palette(canvas, 1, LV_COLOR_RED);
    lv_color_t c0;
    lv_color_t c1;
    c0.full = 0;
    c1.full = 1;

    lv_canvas_fill_bg(canvas, c1);
    uint32_t x, y;
    for (y = 10; y < 30; y++) {
        for (x = 5; x < 20; x++) {
            lv_canvas_set_px(canvas, x, y, c0);
        }
    }
}

• 调用transparent_canvas_demo函数，编译运行