Question

我已将下面的代码嵌入到一个项目中，在该项目中，想要用画笔绘制图片。问题是，如果为主面板编写此代码，一切都很顺利，但是因为我想将它用于现有图像，我看不到画笔。我认为画笔画，但它是前景/背景问题。

//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));
    }
}

Answer 1

这里需要注意的一些重要事项：

图形需要以某种方式保存在管道或中，以便重绘不会消除用户所做的更改。
无限期地保持图形上下文打开是一个坏主意。您应该打开上下文日志，足以将您需要的内容绘制到缓冲区或屏幕上，然后关闭该上下文。
如果要使用屏幕外缓冲区，则需要记住您正在使用的坐标系（“屏幕”与“控制”对比“缓冲区”）。如果你感到困惑，你可能看不到你的期望

考虑到这些概念，您可能会考虑对代码进行以下更改：

// 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));
    }
  }
}

这并不是完美的代码，但是通用模板应该可以工作，让您更接近我认为您正在寻找的东西。希望有所帮助！

Answer 2

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();
        }
    }

用刷子在现有图像上绘画

2 个答案: