C#互動繪圖的實作方法

使用滑鼠螢幕互動繪圖是經常在開發中使用，

下面以畫線為例說明一下實作方法。

public partial class Form1 : Form

{

Boolean bHaveMouse;

Point ptOriginal = new Point();

Point ptLast = new Point();

// Called when the left mouse button is pressed.

public void MyMouseDown(Object sender, MouseEventArgs e)

{

// Make a note that we "have the mouse".

bHaveMouse = true;

// Store the "starting point" for this rubber-band rectangle.

ptOriginal.X = e.X;

ptOriginal.Y = e.Y;

// Special value lets us know that no previous

// rectangle needs to be erased.

ptLast.X = -1;

ptLast.Y = -1;

}

// Convert and normalize the points and draw the reversible frame.

private void MyDrawReversibleLine(Point p1, Point p2)

{

// Convert the points to screen coordinates.

p1 = PointToScreen(p1);

p2 = PointToScreen(p2);

ControlPaint.DrawReversibleLine(p1, p2, Color.Red);

}

// Called when the left mouse button is released.

public void MyMouseUp(Object sender, MouseEventArgs e)

{

// Set internal flag to know we no longer "have the mouse".

bHaveMouse = false;

// If we have drawn previously, draw again in that spot

// to remove the lines.

if (ptLast.X != -1)

{

Point ptCurrent = new Point(e.X, e.Y);

}

Graphics g = this.CreateGraphics();

Pen pen = new Pen(System.Drawing.Color.Black);

g.DrawLine(pen, ptOriginal, ptLast);

pen.Dispose();

g.Dispose();

// Set flags to know that there is no "previous" line to reverse.

ptLast.X = -1;

ptLast.Y = -1;

ptOriginal.X = -1;

ptOriginal.Y = -1;

}

// Called when the mouse is moved.

public void MyMouseMove(Object sender, MouseEventArgs e)

{

Point ptCurrent = new Point(e.X, e.Y);

// If we "have the mouse", then we draw our lines.

if (bHaveMouse)

{

// If we have drawn previously, draw again in

// that spot to remove the lines.

if (ptLast.X != -1)

{

MyDrawReversibleLine(ptOriginal, ptLast);

}

// Update last point.

ptLast = ptCurrent;

// Draw new lines.

MyDrawReversibleLine(ptOriginal, ptCurrent);

}

}

// Set up delegates for mouse events.

protected override void OnLoad(System.EventArgs e)

{

this.Width = 800;

this.Height = 600;

MouseDown += new MouseEventHandler(MyMouseDown);

MouseUp += new MouseEventHandler(MyMouseUp);

MouseMove += new MouseEventHandler(MyMouseMove);

bHaveMouse = false;

}

}

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