TOPIC:

    // get the vpage to calculate the annot size based on current scale value
    PDFVPage *vpage = [m_view vGetPage:0];
    PDFPage *page = [vpage GetPage];
    
    // customize this part to modify the rect size and position
    int x = 50;
    int y = 100;
    int width = 500;
    int height = 100;
    
    // convert the coordinate system from screen to pdf
    struct PDFV_POS pos1;
    struct PDFV_POS pos2;
    
    [m_view vGetPos:&pos1 :(x - self.contentOffset.x) * m_scale :(y - self.contentOffset.y) * m_scale];
    [m_view vGetPos:&pos2 :(x - self.contentOffset.x + width) * m_scale :(y - self.contentOffset.y + height) * m_scale];
    
    PDF_RECT rect;
    
    rect.left = pos1.x;
    rect.right = pos2.x;
    rect.top = pos2.y;
    rect.bottom = pos1.y;
    
    // add the annotation
    [page addAnnotRect:&rect: g_rect_Width * m_scale / [m_view vGetScaleMin:0]: g_rect_color: 0];
    
    // refresh the page
    [m_view vRenderSync:0];
    [self refresh];