Paint（画笔）
Canvas（画布）
The Canvas class holds the "draw" calls.
To draw something, you need 4 basic components: A Bitmap to hold the pixels, a Canvas to host the draw calls (writing into the bitmap), a drawing primitive (e.g. Rect, Path, text, Bitmap), anda paint (to describe the colors and styles for the drawing).
- rotate(float degrees,float px,float py)//对canvas执行旋转变换
scale(float sx,float sy)//对canvas执行缩放skew(float sx,float sy)//对canvas执行倾斜变换translate(float dx,float dy)//移动canvas，向右dx,向下dy- //
- setBitmap(Bitmap bitmap)
Path（绘画路径）
预先在View上将N个点连成一条“路径”，然后调用Canvas的drawPath(path,paint)即可沿着路径绘制图形
//PathmoveTo(float x,float y)//Set the beginning of the next contour to the point (x,y).lineTo(float x,float y)//Add a line from the last point to the specified point (x,y).//canvas-
drawTextOnPath(String text, Path path, float hOffset, float vOffset, Paint paint)//hOffset水平偏移 vOffset垂直偏移
Android还为路径绘制提供了PathEffect来定义绘制效果,PathEffect包含如下子类：
ComposePathEffect CornerPathEffect DashPathEffect DiscretePathEffect PathDashPathEffect SumPathEffect
- Paint paint =newPaint();
paint.setPathEffect(PathEffect effect);
实例：采用双缓冲实现画图板
publicclassDrawView extends View{// 定义记录前一个拖动事件发生点的坐标float preX;float preY;privatePath path;publicPaint paint = null;// 定义一个内存中的图片，该图片将作为缓冲区Bitmap cacheBitmap = null;// 定义cacheBitmap上的Canvas对象Canvas cacheCanvas = null;publicDrawView(Context context,int width ,int height){super(context);// 创建一个与该View相同大小的缓存区cacheBitmap =Bitmap.createBitmap(width, height,Bitmap.Config.ARGB_8888);cacheCanvas =newCanvas();path =newPath();// 设置cacheCanvas将会绘制到内存中的cacheBitmap上cacheCanvas.setBitmap(cacheBitmap);// 设置画笔的颜色paint =newPaint(Paint.DITHER_FLAG);paint.setColor(Color.RED);// 设置画笔风格paint.setStyle(Paint.Style.STROKE);paint.setStrokeWidth(1);// 反锯齿paint.setAntiAlias(true);paint.setDither(true);}@Overridepublic boolean onTouchEvent(MotionEvent event){// 获取拖动事件的发生位置float x = event.getX();float y = event.getY();switch(event.getAction()){caseMotionEvent.ACTION_DOWN:// 从前一个点绘制到当前点之后，把当前点定义成下次绘制的前一个点path.moveTo(x, y);preX = x;preY = y;break;caseMotionEvent.ACTION_MOVE:// 从前一个点绘制到当前点之后，把当前点定义成下次绘制的前一个点path.quadTo(preX, preY, x, y);preX = x;preY = y;break;caseMotionEvent.ACTION_UP:cacheCanvas.drawPath(path, paint);// ①path.reset();break;}invalidate();// 返回true表明处理方法已经处理该事件returntrue;}@Overridepublicvoid onDraw(Canvas canvas){Paint bmpPaint =newPaint();// 将cacheBitmap绘制到该View组件上canvas.drawBitmap(cacheBitmap,0,0, bmpPaint);// ②// 沿着path绘制canvas.drawPath(path, paint);}}
整理自：《疯狂Android讲义》