Thinking more...

GObject、Gio、Gtk、Glib、Clutter 等在範例裡看到的 library，在 Seed 原始碼裡是看不到的，Seed 是利用 GObject Introspection 來跟這些 library 互動。
Cairo、sqlite、readline 的話，因為並沒有使用 GObject 這個 library，所以 Seed 另外寫 Module 來跟這些 library 互動，你可以在 Seed 原始碼的 modules 目錄下看到～

Cairo 實際上是在 Canvas 這個 module 裡，Canvas 裡共有四個主要的類別：CairoCanvas、PDFCanvas、SVGCanvas、ImageCanvas，創建這些 Canvas 以後，基本上都是使用 Cairo 來在這些 Canvas 上繪圖。裡面沒有封裝 cairo_pattern_xxxx、cairo_text_xxxx、cairo_mask...等函數，所以不能用 Cairo 來繪圖或是繪字。

#!/usr/bin/env seed

Seed.import_namespace("Gtk");
Seed.import_namespace("Canvas");
Seed.import_namespace("Gdk");

//
// Initialize GTK+
//
Gtk.init(null, null);

// Create the main application window and set the title
var window = new Gtk.Window({title: "Canvas Demo"});
var vbox = new Gtk.VBox();
var drawingArea = new Gtk.DrawingArea();
var status = new Gtk.Statusbar();
var hbox = new Gtk.HBox();
var exposeEvent = function() { return true;};

//
// create Cairo Canvas
//
function createCairoCanvas()
{
 var cairo = Gdk.cairo_create( drawingArea.window );
 return new Canvas.CairoCanvas( cairo );
}

// 
// Demos from http://cairographics.org/tutorial/
//
function strokeDemo()
{
 drawingArea.window.clear();

 var canvas = createCairoCanvas();
 canvas.strokeStyle = "rgb( 0, 0, 255 )";
 canvas.strokeRect( 10, 10, 50, 50 );
 canvas.stroke();
 return true;
}

function fillDemo()
{
 drawingArea.window.clear();

 var canvas = createCairoCanvas();
 canvas.fillStyle = "rgb( 0, 0, 255 )";
 canvas.fillRect( 10, 10, 50, 50 );
 canvas.fill();
 return true;
}

function fourColorDemo() {
 drawingArea.window.clear();

 var canvas = createCairoCanvas();
 canvas.strokeStyle = "rgb( 0, 0, 0 )";
 canvas.moveTo( 0, 0 );
 canvas.lineTo( 100, 100 );
 canvas.moveTo( 100, 0 );
 canvas.lineTo( 0, 100 );
 canvas.lineWidth = 10;
 canvas.stroke();

 canvas.fillStyle = "rgb( 255, 0, 0 )";
 canvas.globalAlpha = 0.8;
 canvas.fillRect( 0, 0, 50, 50 );

 canvas.fillStyle = "rgb( 0, 255, 0 )";
 canvas.globalAlpha = 0.6;
 canvas.fillRect( 0, 50, 50, 50 );

 canvas.fillStyle = "rgb( 0, 0, 255 )";
 canvas.globalAlpha = 0.4;
 canvas.fillRect( 50, 0, 50, 50 );
 return true;
}

function pathDemo() {
 drawingArea.window.clear();

 var canvas = createCairoCanvas();
 canvas.strokeStyle = "rgb( 255, 0, 0 )";
 canvas.beginPath();
 canvas.moveTo( 25, 25 );
 canvas.lineTo( 50, 37.5 );
 canvas.lineTo( 75, 25 );
 canvas.arc( 50, 50, 25*Math.sqrt(2), -0.25*Math.PI, 0.25*Math.PI, false );
 canvas.bezierCurveTo( 50, 37.5, 50, 62.5, 25, 75 );
 canvas.closePath();
 canvas.stroke();
 return true;
}

function scaleAndTransformDemo() {
 drawingArea.window.clear();

 var canvas = createCairoCanvas();
 canvas.strokeStyle = "rgb( 255, 0, 0 )";
 canvas.lineWidth=10;
 canvas.save();
 canvas.scale( 0.5, 1 );
 canvas.arc( 50, 50, 40, 0, 2*Math.PI, true );
 canvas.stroke();

 canvas.translate( 100, 0 );
 canvas.arc( 50, 50, 40, 0, 2*Math.PI, true );
 canvas.restore();
 canvas.stroke();

 return true;
}

// 
// Demos from http://cairographics.org/samples/
//
function arcDemo() {
 drawingArea.window.clear();

 var canvas = createCairoCanvas();
 var xc = 128;
 var yc = 128;
 var radius = 100;
 var angle1 = 45 * (Math.PI/180);
 var angle2 = 180 * (Math.PI/180);

 canvas.lineWidth = 10;
 canvas.arc( xc, yc, radius, angle1, angle2, true );
 canvas.stroke();

 canvas.fillStyle = "rgb( 255, 51, 51 )";
 canvas.globalAlpha = 0.6;
 canvas.lineWidth = 6;
 canvas.arc( xc, yc, 10, 0, 2*Math.PI, true );
 canvas.fill();

 canvas.arc( xc, yc, radius, angle1, angle2, true );
 canvas.lineTo( xc, yc );
 canvas.arc( xc, yc, radius, angle2, angle2, true );
 canvas.lineTo( xc, yc );
 canvas.stroke();

 return true;
}

function clipDemo() {
 drawingArea.window.clear();

 var canvas = createCairoCanvas();
 canvas.arc( 128, 128, 76.8, 0, 2*Math.PI, true );
 canvas.clip();
 canvas.beginPath();
 canvas.fillRect( 0, 0, 256, 256 );
 canvas.strokeStyle = "rgb( 0, 255, 0)";
 canvas.moveTo( 0, 0 );
 canvas.lineTo( 256, 256 );
 canvas.moveTo( 256, 0 );
 canvas.lineTo( 0, 256 );
 canvas.lineWidth = 10;
 canvas.closePath();
 canvas.stroke();

 return true;
}

function curveRectangleDemo() {
 drawingArea.window.clear();

 var canvas = createCairoCanvas();
 var x0 = 25.6;
 var y0 = 25.6;
 var rect_width = 204.8;
 var rect_height = 204.8;
 var radius = 102.4;
 var x1, y1;

 x1 = x0 + rect_width;
 y1 = y0 + rect_height;
 if( rect_width/2 < radius ) {
  if( rect_height/2<radius ) {
   canvas.moveTo( x0, (y0+y1)/2 );
   canvas.bezierCurveTo( x0, y0, x0, y0, (x0+x1)/2, y0 );
   canvas.bezierCurveTo( x1, y0, x1, y0, x1, (y0+y1)/2 );
   canvas.bezierCurveTo( x1, y1, x1, y1, (x0+x1)/2, y1 );
   canvas.bezierCurveTo( x0, y1, x0, y1, x0, (y0+y1)/2 );
  }
  else {
   canvas.moveTo( x0, y0+raius );
   canvas.bezierCurveTo( x0, y0, x0, y0, (x0+x1)/2, y0 );
   canvas.bezierCurveTo( x1, y0, x1, y0, x1, y0+radius );
   canvas.lineTo( x1, y1-radius );
   canvas.bezierCurveTo( x1, y1, x1, y1, (x1+x0)/2, y1 );
   canvas.bezierCurveTo( x0, y1, x0, y1, x0, y1-radius );
  }
 }
 else {
  if( rect_height/2<radius ) {
   canvas.moveTo( x0, (y0+y1)/2 );
   canvas.bezierCurveTo( x0, y0, x0, y0, x0+radius, y0 );
   canvas.lineTo( x1-radius, y0 );
   canvas.bezierCurveTo( x1, y0, x1, y0, x1, (y0+y1)/2 );
   canvas.bezierCurveTo( x1, y1, x1, y1, x1-radius, y1 );
   canvas.lineTo( x0+radius, y1 );
   canvas.bezierCurveTo( x0, y1, x0, y1, x0, (y0+y1)/2 );
  }
  else {
   canvas.moveTo( x0, y0+radius );
   canvas.bezierCurveTo( x0, y0, x0, y0, x0+radius, y0 );
   canvas.lineTo( x1-radius, y0 );
   canvas.bezierCurveTo( x1, y0, x1, y0, x1, y0+radius );
   canvas.lineTo( x1, y1-radius );
   canvas.bezierCurveTo( x1, y1, x1, y1, x1-radius, y1 );
   canvas.lineTo( x0+radius, y1 );
   canvas.bezierCurveTo( x0, y1, x0, y1, x0, y1-radius );
  }
 }
 canvas.closePath();
 canvas.fillStyle = "rgb( 128, 128, 255 )";
 canvas.fill(); // no fill_preserve(), so you won't see the border.
 canvas.strokeStyle = "rgb( 255, 0, 0 )";
 canvas.globalAlpha = 0.5;
 canvas.lineWidth = 10;
 canvas.stroke();

 return true;
}

function curveToDemo() {
 drawingArea.window.clear();

 var canvas = createCairoCanvas();
 var x=25.6, y=128;
 var x1=102.4, y1=230.4, x2=153.6, y2=25.6, x3=230.4, y3=128.0;

 canvas.moveTo( x, y );
 canvas.bezierCurveTo( x1, y1, x2, y2, x3, y3 );
 canvas.lineWidth = 10;
 canvas.stroke();

 canvas.strokeStyle = "rgb( 255, 51, 51 )";
 canvas.globalAlpha = 0.6;
 canvas.lineWidth = 6;
 canvas.moveTo( x, y ); canvas.lineTo( x1, y1 );
 canvas.moveTo( x2, y2 ); canvas.lineTo( x3, y3 );
 canvas.stroke();

 return true;
}

function rotateDemo() {
 drawingArea.window.clear();

 var canvas = createCairoCanvas();
 canvas.translate( 128, 128 );
 canvas.rotate( 45*Math.PI/180 );
 canvas.scale( 0.9, 0.9 );

 canvas.fillStyle = "rgb(200,0,0)";
 canvas.fillRect( 10, 10, 55, 50 );

 canvas.strokeStyle = "rgb( 0, 200, 0 )";
 canvas.strokeRect( 50, 50, 155, 150 );

 canvas.strokeStyle = "rgb( 0, 0, 255 )";
 canvas.arc( 137.5, 137.5, 100, 0, Math.PI*2, true );
 canvas.stroke();
 return true;
}

//
// routines
//
function createButton( label, handler ) {
 var button = new Gtk.Button( {label: label} );
 button.signal.clicked.connect( handler );
 return button;
}

function createButtonGroup()
{
 var buttonGroup = new Gtk.VBox();
 //var buttonGroup = new Gtk.VButtonBox();
 buttonGroup.pack_start( createButton( "Stroke", function() {
  exposeEvent = strokeDemo;
  return exposeEvent();
 }), true, true);
 buttonGroup.pack_start( createButton( "Fill", function() {
  exposeEvent = fillDemo;
  return exposeEvent();
 }), true, true);
 buttonGroup.pack_start( createButton( "4 color", function() {
  exposeEvent = fourColorDemo;
  return exposeEvent();
 }), true, true);
 buttonGroup.pack_start( createButton( "Path", function() {
  exposeEvent = pathDemo;
  return exposeEvent();
 }), true, true);
 buttonGroup.pack_start( createButton( "Scale and Transform", function() {
  exposeEvent = scaleAndTransformDemo;
  return exposeEvent();
 }), true, true);
 buttonGroup.pack_start( createButton( "Arc", function() {
  exposeEvent = arcDemo;
  return exposeEvent();
 }), true, true);
 buttonGroup.pack_start( createButton( "Clip", function() {
  exposeEvent = clipDemo;
  return exposeEvent();
 }), true, true);
 buttonGroup.pack_start( createButton( "Curve Rectangle", function() {
  exposeEvent = curveRectangleDemo;
  return exposeEvent();
 }), true, true);
 buttonGroup.pack_start( createButton( "Curve To", function() {
  exposeEvent = curveToDemo;
  return exposeEvent();
 }), true, true);
 buttonGroup.pack_start( createButton( "Rotate", function() {
  exposeEvent = rotateDemo;
  return exposeEvent();
 } ), true, true);
 return buttonGroup;
}

//
// Events
//
function drawingArea_ExposeEvent() {
 return exposeEvent();
}

//
// Main
//

// Make the program terminate when the window is closed
window.signal.hide.connect(Gtk.main_quit);

drawingArea.signal.expose_event.connect( drawingArea_ExposeEvent );

hbox.pack_start( createButtonGroup(), false, false);
hbox.pack_start( drawingArea, true, true );

vbox.pack_start( hbox, true, true );
vbox.pack_start( status, false, false, 0);

window.add(vbox);
window.show_all();
window.resize( 640, 480 );

// Start the main GTK+ loop and initiate the program
Gtk.main();

關於這個例子，大部分都是從 Cairo網站上的範例搬來的，也幾乎演示了所有的函數，但還是有少數函數與屬性沒有涵蓋到，如 transform、setTransform、clearRect、quadraticCurveTo...等～
有需要再自己去翻 seed-canvas.c 看吧～