Select Area

[C# Programming]

Hello. I wrote a simple select area, but its working slow when form is maximized, who knows some alternative fast methods for this

here is my code

sry for bad english
public partial class Form1 : Form
{
bool canResize;
int mX, mY;
Rectangle rect = new Rectangle();

public Form1()
{
InitializeComponent();
}

private void Form1_Paint(object sender, PaintEventArgs e)
{
e.Graphics.DrawRectangle(new Pen(Brushes.Purple, 2), rect);
}

private void Form1_MouseDown(object sender, MouseEventArgs e)
{
canResize = true;
mX = e.X; mY = e.Y;

rect.******** = new Point(mX, mY);
}

private void Form1_MouseUp(object sender, MouseEventArgs e)
{
canResize = false;
}

private void Form1_MouseMove(object sender, MouseEventArgs e)
{
if (canResize)
{
if (mX < e.X)
{
rect.X = mX;
rect.Width = e.X - mX;
}
else {
rect.X = e.X;
rect.Width = mX - e.X;
}
if (mY < e.Y)
{
rect.Y = mY;
rect.Height = e.Y - mY;
}
else {
rect.Y = e.Y;
rect.Height = mY - e.Y;
}
this.Invalidate();
}
}
}