如何将面板另存为 BMP

Posted 2023-05-07

【中文标题】如何将面板另存为 BMP

【英文标题】：How to save Panel as BMP

【发布时间】：2013-02-03 15:32:12

【问题描述】：

我正在尝试将面板上的图像保存为 BMP，但无论何时保存，都只有一个空白图像。

绘图代码

    private void DrawingPanel_MouseMove(object sender, MouseEventArgs e)
    
        OldPoint = NewPoint;
        NewPoint = new Point(e.X, e.Y);

        if (e.Button == MouseButtons.Left)
        
            Brush brush = new SolidBrush(Color.Red);
            Pen pen = new Pen(brush, 1);

            DrawingPanel.CreateGraphics().DrawLine(pen, OldPoint, NewPoint);
        
    

保存代码

    void SaveBMP(string location)
    
        Bitmap bmp = new Bitmap((int)DrawingPanel.Width, (int)DrawingPanel.Height);
        DrawingPanel.DrawToBitmap(bmp, new Rectangle(0, 0, DrawingPanel.Width, DrawingPanel.Height));

        FileStream saveStream = new FileStream(location + ".bmp", FileMode.OpenOrCreate);
        bmp.Save(saveStream, ImageFormat.Bmp);

        saveStream.Flush();
        saveStream.Close();
    

最终结果

这是我画的

这就是节省

【问题讨论】：

好吧，您必须将绘画放在面板的绘画事件中，因为面板不会保存您只需“动态”添加的 DrawLine。

您是否尝试过覆盖面板并在覆盖的 OnPaint 方法中对其进行绘制？这是像这样的自定义控件绘图要遵循的一般模式。对我来说，您当前的代码不起作用是有道理的，因为 DrawBitmap 方法可能会再次绘制整个控件，而不是绘制您当前在屏幕上看到的任何内容。

@steinar 我该怎么做呢？能否举例回复一下，谢谢。

【参考方案1】：

您必须更改代码以覆盖 OnPaint 方法。这是自定义控件外观时遵循的默认模式。

您的特定代码不起作用的原因是 DrawToBitmap 必须在调用时重绘整个控件。在这种情况下，该方法不知道您对控件的自定义绘图。

这是一个工作示例：

public partial class DrawingPanel : Panel

    private List<Point> drawnPoints;

    public DrawingPanel()
    
        InitializeComponent();
        drawnPoints = new List<Point>();

        // Double buffering is needed for drawing this smoothly,
        // else we'll experience flickering
        // since we call invalidate for the whole control.
        this.DoubleBuffered = true; 
    

    protected override void OnPaint(PaintEventArgs e)
    
        base.OnPaint(e);

        // NOTE: You would want to optimize the object allocations, 
        // e.g. creating the brush and pen in the constructor
        using (Brush brush = new SolidBrush(Color.Red))
        
            using (Pen pen = new Pen(brush, 1))
            
                // Redraw the stuff:
                for (int i = 1; i < drawnPoints.Count; i++)
                
                    e.Graphics.DrawLine(pen, drawnPoints[i - 1], drawnPoints[i]);
                
            
        
    

    protected override void OnMouseMove(MouseEventArgs e)
    
        base.OnMouseMove(e);

        // Just saving the painted data here:
        if (e.Button == System.Windows.Forms.MouseButtons.Left)
        
            drawnPoints.Add(e.Location);
            this.Invalidate();
        
    

    public void SaveBitmap(string location)
    
        Bitmap bmp = new Bitmap((int)Width, (int)Height);
        DrawToBitmap(bmp, new Rectangle(0, 0, Width, Height));

        using (FileStream saveStream = new FileStream(location + ".bmp", FileMode.OpenOrCreate))
        
            bmp.Save(saveStream, ImageFormat.Bmp);