c# – 用另一个位图擦除部分位图

这不是很难：

>将彩色图像设置为PictureBox的BackgroundImage.
>将黑色图像设置为图像.
>使用普通鼠标事件和透明笔绘制到图像中.

我们需要一个点列表来使用DrawCurve：

List<Point> currentLine = new List<Point>();

我们需要准备并清除黑色层：

private void ClearSheet()
{
    if (pictureBox1.Image != null) pictureBox1.Image.Dispose();
    Bitmap bmp = new Bitmap(pictureBox1.ClientSize.Width,pictureBox1.ClientSize.Height);
    using (Graphics G = Graphics.FromImage(bmp)) G.Clear(Color.Black);
    pictureBox1.Image = bmp;
    currentLine.Clear();
}

private void cb_clear_Click(object sender,EventArgs e)
{
    ClearSheet();
}

要绘制到Image中,我们需要使用关联的Graphics对象..：

void drawIntoImage()
{
    using (Graphics G = Graphics.FromImage(pictureBox1.Image))
    {
        // we want the tranparency to copy over the black pixels
        G.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy;
        G.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
        G.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;

        using (Pen somePen = new Pen(Color.Transparent,penWidth))
        {
            somePen.MiterLimit = penWidth / 2;
            somePen.EndCap = System.Drawing.Drawing2D.LineCap.Round;
            somePen.LineJoin = System.Drawing.Drawing2D.LineJoin.Round;
            somePen.StartCap = System.Drawing.Drawing2D.LineCap.Round;
            if (currentLine.Count > 1)
                G.DrawCurve(somePen,currentLine.ToArray());
        }

    }
    // enforce the display:
    pictureBox1.Image = pictureBox1.Image;
}

通常的鼠标事件：

private void pictureBox1_MouseDown(object sender,MouseEventArgs e)
{
    currentLine.Add(e.Location);
}

private void pictureBox1_MouseMove(object sender,MouseEventArgs e)
{
    if (e.Button == System.Windows.Forms.MouseButtons.Left)
    {
        currentLine.Add(e.Location);
        drawIntoImage();
    }  
}

private void pictureBox1_MouseUp(object sender,MouseEventArgs e)
{
    currentLine.Clear();
}

这就是所需要的.确保保持PB的SizeMode = Normal,否则像素将不匹配..！

请注意,当您想要获得柔化边缘,更多绘画工具,简单点击绘制点或撤消或其他更精细的细节时,存在一些挑战.但基础知识并不难.

顺便说一句,改变Alpha与改变颜色通道没什么不同.

作为替代方案,您可能想要使用TextureBrush：

TextureBrush brush = new TextureBrush(pictureBox1.BackgroundImage);

using (Pen somePen = new Pen(brush) )
{
  // basically 
  // the same drawing code.. 
}

但我发现这个很慢.

更新：

使用png文件作为自定义提示有点困难;主要原因是绘图是相反的：我们不想绘制像素,我们想要清除它们. GDI不支持任何此类组合模式,因此我们需要在代码中执行此操作.

为了加快速度,我们使用两个技巧：LockBits将尽可能快地将区域限制在我们的自定义笔刷尖端将防止浪费时间.

假设您有一个要使用的文件并将其加载到位图中：

string stampFile = @"yourStampFile.png";
Bitmap stamp = null;

private void Form1_Load(object sender,EventArgs e)
{
    stamp = (Bitmap) Bitmap.FromFile(stampFile);
}

现在我们需要一个新功能将它绘制到我们的图像中;而不是DrawCurve我们需要使用DrawImage：

void stampIntoImage(Point pt)
{
    Point point =  new Point(pt.X - stamp.Width / 2,pt.Y - stamp.Height / 2);
    using (Bitmap stamped = new Bitmap(stamp.Width,stamp.Height) )
    {
        using (Graphics G = Graphics.FromImage(stamped))
        {
            stamp.SetResolution(stamped.HorizontalResolution,stamped.VerticalResolution);
            G.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceOver;
            G.DrawImage(pictureBox1.Image,new Rectangle(point,stamped.Size),GraphicsUnit.Pixel);
            writeAlpha(stamped,stamp);
        }
        using (Graphics G = Graphics.FromImage(pictureBox1.Image))
        {
            G.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy;
            G.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
            G.CompositingQuality = 
               System.Drawing.Drawing2D.CompositingQuality.HighQuality;
            G.DrawImage(stamped,point);
        }
    }
    pictureBox1.Image = pictureBox1.Image;
}

一些注意事项：我发现我可以做一个明确的SetResolution,因为我在photoshopped的戳文件是72dpi,我程序中的默认位图是120dpi.注意这些差异！

我通过复制当前图像的右侧部分来启动要绘制的位图.

然后我调用一个快速例程,将例程的alpha应用于它：

void writeAlpha(Bitmap target,Bitmap source)
{
   // this method assumes the bitmaps both are 32bpp and have the same size
    int Bpp = 4;  
    var bmpData0 = target.LockBits(
                    new Rectangle(0,target.Width,target.Height),ImageLockMode.ReadWrite,target.PixelFormat);
    var bmpData1 = source.LockBits(
                    new Rectangle(0,source.Width,source.Height),ImageLockMode.ReadOnly,source.PixelFormat);

    int len = bmpData0.Height * bmpData0.Stride;
    byte[] data0 = new byte[len];
    byte[] data1 = new byte[len];
    Marshal.Copy(bmpData0.Scan0,data0,len);
    Marshal.Copy(bmpData1.Scan0,data1,len);

    for (int i = 0; i < len; i += Bpp)
    {
        int tgtA = data0[i+3];        // opacity
        int srcA = 255 - data1[i+3];  // transparency
        if (srcA > 0) data0[i + 3] = (byte)(tgtA < srcA ? 0 : tgtA - srcA);
    }
    Marshal.Copy(data0,bmpData0.Scan0,len);
    target.UnlockBits(bmpData0);
    source.UnlockBits(bmpData1);
}

我使用一个简单的规则：通过源透明度降低目标不透明度,并确保我们不会消极.你可能想要玩它.

现在我们只需要调整MouseMove;对于我的测试,我添加了两个RadioButtons来在原始圆形笔和自定义标记提示之间切换：

private void pictureBox1_MouseMove(object sender,MouseEventArgs e)
{
    if (e.Button == System.Windows.Forms.MouseButtons.Left)
    {
        if (rb_pen.Checked)
        {
            currentLine.Add(e.Location);
            drawIntoImage();
        }
        else if (rb_stamp.Checked) { stampIntoImage(e.Location); };
    }
}

我没有使用鱼,但你可以看到柔软的边缘：

更新2：这是一个允许简单点击的MouseDown：

private void pictureBox1_MouseDown(object sender,MouseEventArgs e)
{
   if (rb_pen.Checked) currentLine.Add(e.Location);
   else if (rb_stamp.Checked)
   {
       { stampIntoImage(e.Location); };
   }
}