今天一位同事想写一个全屏幕截图的代码。当然要实现的第一步是能够获取整个屏幕的位图，记得Win32 API的CreateDC, BitBlt等函数可以使用。于是上网查了下，果然屏幕截图用这些函数。但winform已经可以把API都忘记了，所以得寻找一个无Win32 API的实现方式。综合了网上的实现，以及自己的一些设计，实现思路如下：
1. 开始截图时，创建一个与屏幕大小一样的位图，然后用Graphics.CopyFromScreen()把屏幕位图拷贝到该位图上。这是很关键的一步，这样所有的操作就都可以在该位图上进行了，而无实际屏幕无关了。
| int width = Screen.PrimaryScreen.Bounds.Width; int height = Screen.PrimaryScreen.Bounds.Height; Bitmap bmp = new Bitmap(width, height); using (Graphics g = Graphics.FromImage(bmp)) { g.CopyFromScreen(0, 0, 0, 0, new Size(width, height)); } |
2. 接下来为了方便在这之上进行截图，有一个很重要的设计实现方式：用全屏幕窗体代替现有真实屏幕，这样就可以把截图过程的所有操作都在那个窗体上实现（该窗体设置成无边框，高宽等于屏幕大小即可），另外为了显示掩蔽效果（只能正常显示选择的部分屏幕内容，而其实部分用一个如半透明层覆盖），就添加一层半透明位置位图。具体代码如下：
| public partial class FullScreenForm : Form { private Rectangle rectSelected = Rectangle.Empty; private bool isClipping = false; private Bitmap screen; private Bitmap coverLayer = null; private Color coverColor; private Brush rectBrush = null; private Bitmap resultBmp = null; public FullScreenForm(Bitmap screen) { InitializeComponent(); int width = Screen.PrimaryScreen.Bounds.Width; int height = Screen.PrimaryScreen.Bounds.Height; coverLayer = new Bitmap(width, height); coverColor = Color.FromArgb(50, 200, 0, 0); rectBrush = new SolidBrush(coverColor); using (Graphics g = Graphics.FromImage(coverLayer)) { g.Clear(coverColor); } this.Bounds = new Rectangle(0, 0, width, height); this.screen = screen; this.DoubleBuffered = true; } protected override void OnMouseDown(MouseEventArgs e) { if (e.Button == MouseButtons.Left) { isClipping = true; rectSelected.Location = e.Location; } else if (e.Button == MouseButtons.Right) { this.DialogResult = DialogResult.OK; } } protected override void OnMouseMove(MouseEventArgs e) { if (e.Button == MouseButtons.Left && isClipping) { rectSelected.Width = e.X - rectSelected.X; rectSelected.Height = e.Y - rectSelected.Y; this.Invalidate(); } } protected override void OnMouseUp(MouseEventArgs e) { if (e.Button == MouseButtons.Left && isClipping) { rectSelected.Width = e.X - rectSelected.X; rectSelected.Height = e.Y - rectSelected.Y; this.Invalidate(); resultBmp = new Bitmap(rectSelected.Width, rectSelected.Height); using (Graphics g = Graphics.FromImage(resultBmp)) { g.DrawImage(screen,new Rectangle(0, 0, rectSelected.Width, rectSelected.Height), rectSelected, GraphicsUnit.Pixel); } this.DialogResult = DialogResult.OK; } } protected override void OnPaint(PaintEventArgs e) { Graphics g = e.Graphics; g.DrawImage(screen, 0, 0); g.DrawImage(coverLayer, 0, 0); PaintRectangle(); } protected override void OnPaintBackground(PaintEventArgs e) { } protected override void OnKeyDown(KeyEventArgs e) { if (e.KeyCode == Keys.Escape) { this.DialogResult = DialogResult.Cancel; } } private void PaintRectangle() { using (Graphics g = Graphics.FromImage(coverLayer)) { g.Clear(coverColor); GraphicsPath path = new GraphicsPath(); path.AddRectangle(this.Bounds); path.AddRectangle(rectSelected); g.FillPath(rectBrush, path); g.DrawRectangle(Pens.Blue, rectSelected); } } public Bitmap ResultBitmap { get { return resultBmp; } } } |
上面的代码都很容易看明白，这里有一个技巧就是GraphicsPath，它自动会形成一个中空的区域。上面的实现很容易扩展：多区域截图，多裁判截图等都很容易实现。
