c# - TextBox with bottom border -

i want have textbox bottom border graphics drawn textbox distorted/broken on resize because of color.transparent.

using code found, able create underlined textbox (drawn rectangle tranparent top, left, right). problem when resize form/window: when resize smaller, resize again expand it, graphics drawn distorted. any fix this?

here photos: the second photo has been resized smaller, larger size.

here's code:

[dllimport("user32")]     private static extern intptr getwindowdc(intptr hwnd);     struct rect {         public int left, top, right, bottom;     }     struct nccalsize_params {         public rect newwindow;         public rect oldwindow;         public rect clientwindow;         intptr windowpos;     }      float clientpadding = 0;     int actualborderwidth = 2;     color bordercolor = color.black;     protected override void wndproc(ref message m) {         //we have change clientsize make room borders         //if not, border limited in how thick is.         if (m.msg == 0x83) { //wm_nccalcsize              if (m.wparam == intptr.zero) {                 rect rect = (rect)marshal.ptrtostructure(m.lparam, typeof(rect));                 rect.left += 2;                 rect.right -= 2;                 rect.top += 0;                 rect.bottom -= 0;// (int)clientpadding;                 marshal.structuretoptr(rect, m.lparam, false);             } else {                 nccalsize_params rects = (nccalsize_params)marshal.ptrtostructure(m.lparam, typeof(nccalsize_params));                 rects.newwindow.left += (int)clientpadding;                 rects.newwindow.right -= (int)clientpadding;                 rects.newwindow.top += (int)clientpadding;                 rects.newwindow.bottom -= 2;                 marshal.structuretoptr(rects, m.lparam, false);             }         }         if (m.msg == 0x85) {//wm_ncpaint                 intptr wdc = getwindowdc(handle);             using (graphics g = graphics.fromhdc(wdc)) {                 controlpaint.drawborder(g, new rectangle(0, 0, size.width, size.height),                     color.transparent, 1, buttonborderstyle.solid,                     color.transparent, 1, buttonborderstyle.solid,                     color.transparent, 1, buttonborderstyle.solid,                     bordercolor, actualborderwidth, buttonborderstyle.solid);             }             return;         }         base.wndproc(ref m);     } 

edit :

found issue, it's because of color.transparent fixed changing color.white, since have white background. then, not case, how prevent "flickering/tearing" while using color.transparent?

to have textbox bottom border, simple workaround can offer docking 1 pixel height lable (or other control) bottom of textbox:

using system.drawing; using system.windows.forms; public class mytextbox : textbox {     public mytextbox()     {         borderstyle = system.windows.forms.borderstyle.none;         autosize = false; //allows change height have bottom padding         controls.add(new label()                     { height = 1, dock = dockstyle.bottom, backcolor = color.black });     } }