二维绘图上下文.doc

二维绘图上下文 当使用一个 canvas 元素的 getContext(“2d”)方法时，返回的是 CanvasRenderingContext2D对象，其内部表现为笛卡尔平面坐标，并且左上 角坐标为(0,0)，在本平面中往右则 x 坐标增加和往下方 y 坐标增加。每一 个canvas元素仅有一个上下文对象。其接口如下： interface CanvasRenderingContext2D { // back-reference to the canvas readonly attribute HTMLCanvasElement canvas; // state void restore(); // pop state stack and restore state void save();// push state on state stack // transformations (default transform is the identity matrix) void rotate(in float angle); void scale(in float x, in float y); void setTransform(in float m11, in float m12, in float m21, in float m22, in float dx, in float dy); void transform(in float m11, in float m12, in float m21, in float m22, in float dx, in float dy); void translate(in float x, in float y); // compositing attribute float globalAlpha; // (default 1.0) attribute DOMString globalCompositeOperation; // (default source-over) // colors and styles attribute any fillStyle; // (default black) attribute any strokeStyle; // (default black) CanvasGradient createLinearGradient(in float x0,in floaty0,in float x1, in float y1); CanvasGradient createRadialGradient(in float x0,in floaty0,in float r0, in float x1, in float y1, in float 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 styles attribute DOMString lineCap; // butt, round, square (default butt) attribute DOMString lineJoin; // miter, round, bevel (default miter) attribute float lineWidth; // (default 1) attribute float miterLimit; // (default 10) // shadows attribute float shadowBlur; // (default 0) attribute DOMString shadowColor; // (default transparent black) attribute float shadowOffsetX; // (default 0) attribute float shadowOffsetY; // (default 0) // rects void clearRect(in float x, in float y, in float w, in float h); vo