一、DrawingArea连续实时绘图

图看上去不是很清晰，KAZAM录屏AVI尺寸80MB， 转换成gif后10MB, 按CSDN对GIF要求，把它剪裁缩小压缩成了上面的GIF，图像质量大不如原屏AVI，但应该能说明原意：随机数据随时间绘制在 gtk 的 drawingArea 上，曲线左移后继续绘制，形成连续的实时数据绘图。

1. 在窗体上放置控件 drawingarea1

drawingarea1是 gtk 的组件，它是 gdk 窗口的一个框，绘图域是 gdkwindow

2. 内存中创建一个足够大的cario图像和cairo context上下文

        drawingarea1Width = drawingarea1.Allocation.Width;drawingarea1Height = drawingarea1.Allocation.Height;//surfacepub = new ImageSurface(Format.ARGB32, drawingarea1Width, drawingarea1Height);surfacepub = new ImageSurface(Format.ARGB32, 1920, 1080);ctxpub = new Cairo.Context(surfacepub);

drawingarea1Width和drawingarea1Height 是读取的drawingarea1的宽高尺寸，surfacepub是内存中的图像的surface，ctxpub 是 surface 的 Cairo Context

3. 在gdk的timer事中判断是否绘图点超界，超界了调用moveleft函数让绘图点左移500个像素，衔接绘图。

  private Boolean OnTimedEvent1(){drawingarea1Width = drawingarea1.Allocation.Width;drawingarea1Height = drawingarea1.Allocation.Height;iArea1ObjX += 10;if (iArea1ObjX > drawingarea1Width){moveleft();int movdiff = 500;iArea1ObjX = drawingarea1Width-movdiff;iOldX2 = iOldX2 - movdiff; iOldX1 = iOldX1 - movdiff;//Mark by write Moved!Gdk.GC gc = new Gdk.GC(drawingarea1.GdkWindow);gc.RgbFgColor = new Gdk.Color(0, 0, 0);drawingarea1.GdkWindow.DrawRectangle(gc, true, iOldX2, 0, drawingarea1Width, drawingarea1Height);gc.RgbFgColor = new Gdk.Color(255,255,255);var layout = new Pango.Layout(PangoContext);layout.SetText("Moved!");layout.FontDescription = Pango.FontDescription.FromString("Serif 12");drawingarea1.GdkWindow.DrawLayout(gc, iOldX2, iOldY2, layout);gc.Dispose();DestroyContext();CreateContext();}ctxpub.MoveTo(iArea1ObjX, iArea1ObjY);ctxpub.SetSourceRGB(1, 0, 0);// Drawvar rand = new Random();iArea1ObjY = rand.Next(10, 150);iOldX1 = iOldX2; iOldY1 = iOldY2;iOldX2 = iArea1ObjX; iOldY2 = iArea1ObjY;ctxpub.MoveTo(iOldX1, iOldY1);ctxpub.LineTo(iArea1ObjX, iArea1ObjY);ctxpub.ClosePath();ctxpub.Stroke();ctxArea1 = Gdk.CairoHelper.Create(drawingarea1.GdkWindow);surfacepub.Show(ctxArea1, 0, 0);ctxArea1.Dispose();return true;}

4. drawingarea1 图像左移 moveleft

    private void moveleft(){int movdiff = 500;Gdk.Pixbuf pixbuf = new Gdk.Pixbuf(Gdk.Colorspace.Rgb, false, 8, drawingarea1Width, 1080);pixbuf = pixbuf.GetFromDrawable(drawingarea1.GdkWindow, Gdk.Colormap.System, movdiff, 0, 0, 0, (drawingarea1Width-movdiff), 1080);Gdk.Pixbuf pixbuf1 = new Gdk.Pixbuf(Gdk.Colorspace.Rgb, false, 8, drawingarea1Width, 1080);pixbuf.CopyArea(movdiff, 0, drawingarea1Width, 1080, pixbuf1, 0, 0);Gdk.GC gc = new Gdk.GC(drawingarea1.GdkWindow);drawingarea1.GdkWindow.DrawPixbuf(gc, pixbuf, 0, 0, 0, 0, drawingarea1Width, 1080, Gdk.RgbDither.None, 0, 0);pixbuf.Dispose();pixbuf1.Dispose();gc.Dispose();}

5.  释放内存surface和其cairo context

    private void DestroyContext(){surfacepub.Dispose();ctxpub.Dispose();}

如果在内存surface上显示Hello World, 将图像存成 png 是下面的样子。大小只有4kb，是镂空的，如果在photoshop上的话可以放在任何图层上，在上面的程序中也可以将它拓印到任何共它surface上，drawingarea1.GdkWindow也是一个surface

二、用Cario贴图做连续图形

创建两个完全相同的内存 surfacepub 和 surfacebak，两个相同的context ctxpub和 context ctxbak,再创建一个drawingarea的context ctxArea1

    private void CreateContext(){drawingarea1Width = drawingarea1.Allocation.Width;drawingarea1Height = drawingarea1.Allocation.Height;surfacepub = new ImageSurface(Format.ARGB32, 1920, 1080);surfacebak = new ImageSurface(Format.ARGB32, 1920, 1080);ctxpub = new Cairo.Context(surfacepub);ctxbak = new Cairo.Context(surfacebak);ctxArea1 = Gdk.CairoHelper.Create(drawingarea1.GdkWindow);}

程序退出时记得把它们全弃用掉

    private void DestroyContext(){surfacepub.Dispose();surfacebak.Dispose();ctxpub.Dispose();ctxbak.Dispose();ctxArea1.Dispose();}

在gdk timer事件中完成移动和绘图

    private Boolean OnTimedEvent1(){drawingarea1Width = drawingarea1.Allocation.Width;drawingarea1Height = drawingarea1.Allocation.Height;//下一个绘图点 xiArea1ObjX += 10;//判断若是超出边界if (iArea1ObjX > drawingarea1Width){//超出的话减掉500个像素点int movdiff = 500;iArea1ObjX = drawingarea1Width - movdiff;iOldX1 = iOldX1 - movdiff; iOldX2 = iOldX2 - movdiff;iArea1ObjX += 10;//用黑色清除 surfacebakctxbak.SetSourceColor(new Cairo.Color(0, 0, 0));ctxbak.Rectangle(0, 0, drawingarea1Width, drawingarea1Height);ctxbak.Fill();//左移500个像素点后将 surfacepub 印在 ctxbak 所指的 surfacebak 上surfacepub.Show(ctxbak, -1*movdiff, 0);//将空余出的地方用黑色填充ctxbak.SetSourceColor(new Cairo.Color(0, 0, 0));ctxbak.Rectangle(drawingarea1Width-movdiff, 0, drawingarea1Width, drawingarea1Height);ctxbak.Fill();//用白色在 surfacebak 上写字 "Moved!"ctxbak.SetSourceColor(new Cairo.Color(1, 1, 1));ctxbak.MoveTo(iOldX1, iOldY1);ctxbak.ShowText("Moved!");ctxbak.Stroke();//清除掉 surfacepubctxpub.SetSourceColor(new Cairo.Color(0, 0, 0));ctxpub.Rectangle(0, 0, drawingarea1Width, drawingarea1Height);ctxpub.Fill();//将 surfacebak 上的内容印在 surfacepub上surfacebak.Show(ctxpub, 0, 0);}//在 surfacepub 上画线var rand = new Random();iArea1ObjY = rand.Next(10, 150);iOldX1 = iOldX2; iOldY1 = iOldY2;iOldX2 = iArea1ObjX; iOldY2 = iArea1ObjY;ctxpub.MoveTo(iOldX1, iOldY1);ctxpub.SetSourceRGB(1, 0, 0);ctxpub.LineTo(iArea1ObjX, iArea1ObjY);ctxpub.Stroke();//创建 drawingarea1 的 contextctxArea1 = Gdk.CairoHelper.Create(drawingarea1.GdkWindow);//将 surfacepub 印在 drawingarea1 上显示surfacepub.Show(ctxArea1, 0, 0);//释放掉 drawingarea1 的 contextctxArea1.Dispose();//返回 true ， 以便 timer 继续return true;}

由于图像是在内存的surfacepub上完成后印在drawingarea上的，因此曲线不受屏幕和组件变化影响，或是说即使受到破坏，但下一次镂印显示时又是内存中完整的图像。

GdkWindow直接在组件屏幕上绘图和用Cairo在内存中连续绘图均完美显现，前者像是windows方式做图，后者比前者感觉更灵巧一些。