HTML5 Canvas编写五彩连珠（1）：预览

HTML5推出也有很长一段时间了，一直没有学习过，闲来无事学习开发个游戏吧。用javascript+canvas编写一个五彩连珠的游戏。
Canvas 画布
标签<canvas id="canvas" ></canvas>，很简单和普通的tag没区别。关键在于js对他的操作。先看个示例代码：
<canvas id="canvas" height="100" width="100"></canvas>
<script>
    var canvas = document.getElementById("canvas");
    var ctx = canvas.getContext("2d");
    ctx.beginPath();
    ctx.moveTo(50,10);
    ctx.lineTo(50,90);
    ctx.moveTo(10,50);
    ctx.lineTo(90,50);

    ctx.strokeStyle="red";
    ctx.stroke();
</script>
你能看到想到我画的是什么吗？ ctx是canvas的绘制的类型2D的，以后会支持3D，那木，目前基于canvas的绘制都是调用2d context的方法。所以要了解绘制各种图形，得先看看他的api。
interface CanvasRenderingContext2D {

// back-reference to the canvas
readonly attribute HTMLCanvasElement canvas;

// state
void save(); // push state on state stack
void restore(); // pop state stack and restore state
// transformations (default transform is the identity matrix)
void scale(in double x, in double y);
void rotate(in double angle);
void translate(in double x, in double y);
void transform(in double a, in double b, in double c, in double d, in double e, in double f);
void setTransform(in double a, in double b, in double c, in double d, in double e, in double f);
// compositing
           attribute double globalAlpha; // (default 1.0)
           attribute DOMString globalCompositeOperation; // (default source-over)
// colors and styles
           attribute any strokeStyle; // (default black)
           attribute any fillStyle; // (default black)
CanvasGradient createLinearGradient(in double x0, in double y0, in double x1, in double y1);
CanvasGradient createRadialGradient(in double x0, in double y0, in double r0, in double x1, in double y1, in double r1);
CanvasPattern createPattern(in HTMLImageElement image, in DOMString repetition);
CanvasPattern createPattern(in HTMLCanvasElement image, in DOMString repetition);
CanvasPattern createPattern(in HTMLVideoElement image, in DOMString repetition);

// line caps/joins
           attribute double lineWidth; // (default 1)
           attribute DOMString lineCap; // "butt", "round", "square" (default "butt")
           attribute DOMString lineJoin; // "round", "bevel", "miter" (default "miter")
           attribute double miterLimit; // (default 10)

// shadows
           attribute double shadowOffsetX; // (default 0)
           attribute double shadowOffsetY; // (default 0)
           attribute double shadowBlur; // (default 0)
           attribute DOMString shadowColor; // (default transparent black)

// rects
void clearRect(in double x, in double y, in double w, in double h);
void fillRect(in double x, in double y, in double w, in double h);
void strokeRect(in double x, in double y, in double w, in double h);

// path API
void beginPath();
void closePath();
void moveTo(in double x, in double y);
void lineTo(in double x, in double y);
void quadraticCurveTo(in double cpx, in double cpy, in double x, in double y);
void bezierCurveTo(in double cp1x, in double cp1y, in double cp2x, in double cp2y, in double x, in double y);
void arcTo(in double x1, in double y1, in double x2, in double y2, in double radius);
void rect(in double x, in double y, in double w, in double h);
void arc(in double x, in double y, in double radius, in double startAngle, in double endAngle, in optional boolean anticlockwise);
void fill();
void stroke();
void clip();
boolean isPointInPath(in double x, in double y);

// Focus management
boolean drawFocusRing(in Element element, in optional boolean canDrawCustom);

// Caret and selection management
long caretBlinkRate();
boolean setCaretSelectionRect(in Element element, in double x, in double y, in double w, in double h);

// text
           attribute DOMString font; // (default 10px sans-serif)
           attribute DOMString textAlign; // "start", "end", "left", "right", "center" (default: "start")
           attribute DOMString textBaseline; // "top", "hanging", "middle", "alphabetic", "ideographic", "bottom" (default: "alphabetic")
void fillText(in DOMString text, in double x, in double y, in optional double maxWidth);
void strokeText(in DOMString text, in double x, in double y, in optional double maxWidth);
TextMetrics measureText(in DOMString text);

// drawing images
void drawImage(in HTMLImageElement image, in double dx, in double dy, in optional double dw, in double dh);
void drawImage(in HTMLImageElement image, in double sx, in double sy, in double sw, in double sh, in double dx, in double dy, in double dw, in double dh);
void drawImage(in HTMLCanvasElement image, in double dx, in double dy, in optional double dw, in double dh);
void drawImage(in HTMLCanvasElement image, in double sx, in double sy, in double sw, in double sh, in double dx, in double dy, in double dw, in double dh);
void drawImage(in HTMLVideoElement image, in double dx, in double dy, in optional double dw, in double dh);
void drawImage(in HTMLVideoElement image, in double sx, in double sy, in double sw, in double sh, in double dx, in double dy, in double dw, in double dh);

// pixel manipulation
ImageData createImageData(in double sw, in double sh);
ImageData createImageData(in ImageData imagedata);
ImageData getImageData(in double sx, in double sy, in double sw, in double sh);
void putImageData(in ImageData imagedata, in double dx, in double dy, in optional double dirtyX, in double dirtyY, in double dirtyWidth, in double dirtyHeight);
};

interface CanvasGradient {
// opaque object
void addColorStop(in double offset, in DOMString color);
};

interface CanvasPattern {
// opaque object

补充：web前端 , HTML 5 ,