C# 在现有图像上使用笔刷绘制

我已经将下面的代码嵌入到一个项目中，其中一个用户希望用画笔在图片上画画。问题是，如果一个用户为一个主面板编写这段代码，一切都会顺利进行，但由于我想将其用于现有图像，我看不到画笔。我想画笔会画画，但这是前景/背景的问题

//the first line goes to the main form  - under the initialize component
graphics = DisplayPicturebox.CreateGraphics();

bool draw = false;
Graphics graphics;

private void DisplayPicturebox_MouseDown(object sender, MouseEventArgs e)
{
    draw = true;
}

private void DisplayPicturebox_MouseUp(object sender, MouseEventArgs e)
{
    draw = false;
}

private void DisplayPicturebox_MouseMove(object sender, MouseEventArgs e)
{
    if (draw)
    {
        //create a brush:
        SolidBrush MysolidBrush = new SolidBrush(Color.Red);
        graphics.FillEllipse(MysolidBrush, e.X, e.Y,
                      Convert.ToInt32(toolStripTextBox1.Text),
                      Convert.ToInt32(toolStripTextBox1.Text));
    }
}

---

这里需要注意的几个重要事项：

• 图形需要在管道中处理或以某种方式保存，以便重新绘制不会消除用户所做的更改

• 保持图形上下文无限期地打开是个坏主意。您应该打开上下文日志，以便将所需内容绘制到缓冲区或屏幕，然后关闭该上下文

• 如果你想使用屏幕外的缓冲区，你需要记住你正在使用的坐标系（“屏幕”对“控制”，对“缓冲”）。如果你感到困惑，你可能看不到你所期望的

记住这些概念，您可以考虑以下代码的更改：

// at the beginning of your class declare an offscreen buffer
private System.Drawing.Bitmap buffer;

// .. later create it in the constructor
public Form1() {
  InitializeComponent();

  // use the w/h of the picture box here
  buffer = new System.Drawing.Bitmap(picBox.Width, picBox.Height);
}

// in the designer add a paint event for the picture box:
private picBox_Paint(object sender, System.Windows.Forms.PaintEventArgs e) {
   e.Graphics.DrawImageUnscaled(buffer);
}

// finally, your slightly modified painting routine...
private picBox__MouseMove(object sender, MouseEventArgs e)
{
  if (draw)
  {
    using (var context = System.Drawing.Graphics.FromImage(buffer)) {
      //create a brush:
      SolidBrush MysolidBrush = new SolidBrush(Color.Red);
      graphics.FillEllipse(MysolidBrush, e.X, e.Y,
                    Convert.ToInt32(toolStripTextBox1.Text),
                    Convert.ToInt32(toolStripTextBox1.Text));
    }
  }
}

---

这并不意味着是完美的代码，但通用模板应该可以工作，让您更接近我认为您正在寻找的内容。希望对你有所帮助

试试这个，修改mousemove事件：

private void DisplayPicturebox_MouseMove(object sender, MouseEventArgs e)
    {
        if (draw)
        {
            graphics = DisplayPicturebox.CreateGraphics();
            SolidBrush MysolidBrush = new SolidBrush(Color.Red);
            float newX = (float)DisplayPicturebox.Image.Size.Width / (float)DisplayPicturebox.Size.Width;
            float newY = (float)DisplayPicturebox.Image.Size.Height / (float)DisplayPicturebox.Size.Height;
            graphics = Graphics.FromImage(DisplayPicturebox.Image);

            graphics.FillEllipse(MysolidBrush, e.X * newX, e.Y * newY, Convert.ToInt32(toolStripTextBox1.Text), Convert.ToInt32(toolStripTextBox1.Text));
            DisplayPicturebox.Refresh();
        }
    }

---

我已经编辑了你的标题。请参阅“”，其中的共识是“不，他们不应该”。