绘制文本编辑框中的光标等的思路

/**
  * @brief 获取字符串中某个index的子串占位rect
  * @param ctx ui上下文
  * @param wgt    widget ui组件
  * @param style 文字样式（和draw方法必须相同，否则会不一致）
  * @param indx 字符在字符串中的index
  * @return 占位rect
  */
static gui_rect_t gui_itxt_indx_rect(gui_context_p ctx, gui_widget_p wgt, gui_text_style_t style, int indx)
{
    char* str = wgt->text;
    int num = indx+1;
    char txt[num+1];
    int j;
    for(j = 0; j<num; j++){
        txt[j] = *(str+j);
    }
    txt[num] = '\0';
   
    gui_rect_t rect = gui_base_measuretext(ctx->context, wgt->px, wgt->py, 65535, wgt->ph, txt, style);
    return rect;
}

/**

 * @brief 获取鼠标在文本中的位置和字符index(用于绘制文字中的光标和选中背景)

 * @param ctx ui 上下文

 * @param wgt widget ui组件

 * @param x 点击坐标x

 * @param y 点击坐标x

 * @param style 文字样式（和draw方法必须相同，否则会不一致）

 * @param indx 用于返回字符在字符串中的index

 * @param rec 占位rect

 */
static void gui_itxt_measure_pos(gui_context_p ctx, gui_widget_p wgt, int x, int y,
    gui_text_style_t style, int* indx, gui_rect_t* rec)
{
    gui_rect_t rect = {0};
    char* str = wgt->text;
    if(!str || strlen(str)<1)return;
    int m = 0;
    int n = strlen(str)-1;
    int i;
    byte bol = 0;//
    while(n - m > 4){//因为是多字节字符的字符串，汉字占两个字节，两个相邻汉字差4个char
        i=0;
        int mid = (m+n)/2;
        while(i <= mid){
            if(*(str+i)<0){
                if(i == mid){i--;break;}//汉字不能完整舍弃
                if(i == mid-1){i++;break;}//汉字刚好占满结束
                i+=2;
            }else{
                if(i == mid)break;
                i++;
            }
        }

        rect = gui_itxt_indx_rect(ctx, wgt, style, i);
        
        if(rect.x+rect.w > x){
            n = i;
        }else if(rect.x+rect.w < x){
            m = i+1;
        }else{//点击位置正好为光标位置
            bol = 1;
            break;
        }
    }
    if(bol){
        rec->x = rect.x;
        rec->y = rect.y;
        rec->w = rect.w-2;//-2为一点差值，根据实际测试得来
        rec->h = rect.h;
        *indx = i;
        return;
    }
   
    while(m <= n){//小于4个char逐char定位
        byte bla = *(str+m) < 0;//同样需要处理汉字
        int rlm = bla?m+1:m;
        rect = gui_itxt_indx_rect(ctx, wgt, style, rlm);
        *indx = rlm;
        if(x < rect.x+rect.w){
            if(m == 0){//第0个字符处理
                int per = rect.w/2;//用于处理电子字符左右半边，定位该字符前后
                if(x <= rect.x + per){
                    rect.w=3;
                    *indx = -1;
                }
            }else{
                gui_rect_t recta = gui_itxt_indx_rect(ctx, wgt, style, m-1);
                int pera = (rect.w - recta.w)/2;//用于处理电子字符左右半边，定位该字符前后
                if(x <= recta.x + recta.w + pera - 2){
                    rect = recta;
                    *indx = m-1;
                }
            }
            break;
        }
        if(bla)m+=2;
        else m++;
    }
   
    rec->x = rect.x;
    rec->y = rect.y;
    rec->w = rect.w-2;//-2为一点差值，根据实际测试得来
    rec->h = rect.h;

}