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);
// Draw
var 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 x
iArea1ObjX += 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 surfacebak
ctxbak.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 surfacepub
ctxpub.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 context
ctxArea1 = Gdk.CairoHelper.Create(drawingarea1.GdkWindow);
//将 surfacepub 印在 drawingarea1 上显示
surfacepub.Show(ctxArea1, 0, 0);
//释放掉 drawingarea1 的 context
ctxArea1.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。