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I want to have TextBox with bottom border but Graphics drawn for TextBox is distorted/broken on resize because of Color.Transparent.

Using an code I found, I was able to create a underlined TextBox (Drawn Rectangle with tranparent top, left, right). The problem is when I resize the form/window: when I resize it to smaller, then resize again to expand it, the graphics drawn is distorted. Any fix for this?

Here are photos: The second photo has been already resized smaller, then back to a larger size. NormalContracted then Expanded

Here's the 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 to change the clientsize to make room for borders //if not, the border is limited in how thick it 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 :

I already found the issue, it's because of the Color.Transparent I fixed it by changing it to Color.White, since I have a white background. But then, that would not always be the case, how would I prevent that "Flickering/Tearing" while using Color.Transparent?

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  • TextBox doesn't like being drawn on; the graphics will be wiped out pretty much immediately and all those tricks only help so much.. The effect you see is called 'tearing'. You'd better create a real form with Labels and plain TextBoxes.. Commented Jul 15, 2016 at 19:14
  • Transparency is not really supported in Winforms. TextBox doesn't support it at all. Commented Jul 15, 2016 at 19:29

2 Answers 2

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To have a TextBox with bottom border, The most simple workaround that I can offer is docking a 1 pixel height lable (or other control) to bottom of the TextBox:

using System.Drawing; using System.Windows.Forms; public class MyTextBox : TextBox { public MyTextBox() { BorderStyle = System.Windows.Forms.BorderStyle.None; AutoSize = false; //Allows you to change height to have bottom padding Controls.Add(new Label() { Height = 1, Dock = DockStyle.Bottom, BackColor = Color.Black }); } }
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8 Comments

@Yawz I saw your edit. You can use White color to render those invisible borders, but It also makes flickering when you move mouse over the control. Currently I prefer to use this workaround which I shared.
This doesn't answer directly my question, but it's a solves my problem in a different approach, but how can I create a padding for the text? See this Screenshot: oi67.tinypic.com/10zvgqu.jpg I hope to give it padding on right and left sides, and a margin to raise the text..
• For padding between Text and Line: it's enough to set AutoSize property in constructor to false. • For setting left padding and right padding, you should send EM_SETMARGINS message to the TextBox. You will find this post helpful: NumericUpDown with Unit I've set left padding in answer, and in comments added right padding too.
I'm a newbie and literally don't know how to use that code to give my text box a left and right margin, anyways I will accept this. Here's my code where I don't know how to implement the left and right padding for the text.. pastebin.com/3AgtNZqx I am hoping for a result like this: imgur.com/2In0DQB .. I tried but I can't implement, I hope you have a solution for this..
@HmH TextBox.Controls[0] is the label. You can also create a public property to expose it.
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0 
 this.TxtBox.BorderStyle = System.Windows.Forms.BorderStyle.None;
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