Android群英传读书笔记第六章(Android绘图机制与处理技巧)

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笔记

尺寸单位转换

   public static int dp2px(int dp, Context context) {return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp,context.getResources().getDisplayMetrics());}public static int dip2px(int dip,Context context){float scale = context.getResources().getDisplayMetrics().density;return (int) (dip*scale+0.5f);}public static int sp2px(int sp,Context context){float scale = context.getResources().getDisplayMetrics().scaledDensity;return (int) (sp*scale+0.5f);}

Android绘图
先看下Canvas的操作

save():将所有之前绘制的图像保存起来，让后续的操作好像在一个新的图层一样
restore():将save之后绘制的图像和save之前的图像合并。
translate()和rotate():画布平移旋转，也可以理解过坐标的平移旋转，这样更加好理解。

接下来我们绘制一个表盘。

public class ClockView extends View {Paint circlePaint = new Paint(Paint.ANTI_ALIAS_FLAG);Paint degreePaint = new Paint(Paint.ANTI_ALIAS_FLAG);Paint hourPaint = new Paint(Paint.ANTI_ALIAS_FLAG);Paint minutePaint = new Paint(Paint.ANTI_ALIAS_FLAG);private int height;private int width;public ClockView(Context context, AttributeSet attrs) {super(context, attrs);init();}public void init(){circlePaint.setStyle(Paint.Style.STROKE);circlePaint.setStrokeWidth(5);circlePaint.setColor(Color.RED);hourPaint.setStrokeWidth(10);minutePaint.setStrokeWidth(8);}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {super.onMeasure(widthMeasureSpec, heightMeasureSpec);height = getMeasuredHeight();width = getMeasuredWidth();}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);canvas.drawCircle(width/2,height/2,width/2,circlePaint);drawDegree(canvas);drawHourAndMinute(canvas);}private void drawHourAndMinute(Canvas canvas) {canvas.save();canvas.translate(width/2,height/2);canvas.drawLine(0,0,100,100,hourPaint);canvas.drawLine(0,0,200,100,minutePaint);canvas.drawRect(0,0,20,20,hourPaint);canvas.restore();}public void drawDegree(Canvas canvas){for (int i = 0; i < 24; i++) {if(i==0||i==6||i==12||i==18){degreePaint.setStrokeWidth(5);degreePaint.setTextSize(30);canvas.drawLine(width/2,height/2-width/2,width/2,height/2 - width/2+60,degreePaint);String degree = String.valueOf(i);canvas.drawText(degree,width/2-degreePaint.measureText(degree)/2,height/2-width/2+90,degreePaint);}else{degreePaint.setStrokeWidth(3);degreePaint.setTextSize(20);canvas.drawLine(width/2,height/2-width/2,width/2,height/2 - width/2+30,degreePaint);String degree = String.valueOf(i);canvas.drawText(degree,width/2-degreePaint.measureText(degree)/2,height/2-width/2+60,degreePaint);}canvas.rotate(15,width/2,height/2);}}
}

Layer图层
通过saveLayer()来创建一个图层，基于栈的结构进行管理。
相关方法：
saveLayer();
saveLayerAlpha()
restore:()
restoreToCount()

色彩特效处理
这里写图片描述

变换颜色值的两种方法

改变偏移量
改变颜色系数

颜色效果处理
色调：matrix.setRotate();
饱和度：matrix.setSaturation();
亮度：matrix.setScale();

Android系统不允许修改原图，要先创建一个原图的副本，然后利用这个副本创建一个画布，最后把原图绘制到画布中。

  Bitmap bmp = Bitmap.createBitmap(bm.getWidth(),bm.getHeight(), Bitmap.Config.ARGB_8888);Canvas canvas = new Canvas(bmp);Paint paint  = new Paint();canvas.drawBitmap(bm,0,0,paint);

通过ColorMatrix的set方法，可以将一个一维数组转化为ColorMatrix
这里写图片描述

Android图形处理
Android的图形变换是一个3X3的矩阵，图形变化的初始矩阵也是对角线全部为1的矩阵

图形变化包含下面四个基本操作

平移
旋转
缩放
错切

Shader
- BitmapShader
- LinearGradient
- RadiaGradient
- SweepGradient
- ComposeShader

填充模式

CLAMP:拉伸，拉伸的是图片的最后一个像素，不断重复
REPEAT:重复：横向，纵向不断重复
MIRROR:镜像：横向不断重复旋转，纵向不断重复旋转

SurfaceView
Android系统通过发出VSYNC信号来进行屏幕的重绘，刷新的时间间隔为16ms.

SurfaceView和View的区别
- View主要适用于主动更新情况，而SurfaceView主要适用于被动更新，例如频繁的刷新
- View在主线程中对画面刷新，而SurfaceView会通过一个子线程来刷新
- SurfaceView在底层实现了双缓冲机制
- 当程序需要更新View上的图像时，程序必须重绘View上显示的整张图片

如果你的自定义View需要频繁刷新，或者刷新时数据量比较大，就可以使用SurfaceView了。下面来看两个SurfaceView的例子

绘制正弦曲线

这里写图片描述

public class MySurfaceView extends SurfaceView implements SurfaceHolder.Callback,Runnable {private SurfaceHolder surfaceHolder;private Canvas canvas;private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);//控制子线程private boolean mIsDrawing;private int x = 0;private int y;private Path mPath = new Path();public MySurfaceView(Context context, AttributeSet attrs) {super(context, attrs);surfaceHolder = getHolder();surfaceHolder.addCallback(this);setFocusable(true);setFocusableInTouchMode(true);setKeepScreenOn(true);paint.setColor(Color.RED);paint.setStyle(Paint.Style.STROKE);paint.setStrokeWidth(5);}/*** surfaceview创建* @param holder*/@Overridepublic void surfaceCreated(SurfaceHolder holder) {mIsDrawing = true;new Thread(this).start();}/*** surfaceview改变* @param holder* @param format* @param width* @param height*/@Overridepublic void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {}/*** surfaceview销毁* @param holder*/@Overridepublic void surfaceDestroyed(SurfaceHolder holder) {mIsDrawing = false;}@Overridepublic void run() {while(mIsDrawing){draw();x+=1;y = (int) (100*Math.sin(x*2*Math.PI/180)+400);mPath.lineTo(x,y);}}public void draw(){try {canvas = surfaceHolder.lockCanvas();//设置画布背景颜色canvas.drawColor(Color.WHITE);canvas.drawPath(mPath,paint);}catch (Exception e){}finally {//对画布内容进行提交，放在finally里面可以保证执行if(canvas!=null){surfaceHolder.unlockCanvasAndPost(canvas);}}}
}

画布

这里写图片描述

public class SurfaceViewCanvas extends SurfaceView implements SurfaceHolder.Callback,Runnable {private SurfaceHolder mHolder;private Canvas canvas;private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);private boolean mIsDrawing;private Path mPath = new Path();public SurfaceViewCanvas(Context context, AttributeSet attrs) {super(context, attrs);mHolder = getHolder();mHolder.addCallback(this);setFocusable(true);setFocusableInTouchMode(true);setKeepScreenOn(true);paint.setColor(Color.RED);paint.setStyle(Paint.Style.STROKE);paint.setStrokeWidth(10);}@Overridepublic void surfaceCreated(SurfaceHolder holder) {mIsDrawing = true;}@Overridepublic void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {new Thread(this).start();}@Overridepublic void surfaceDestroyed(SurfaceHolder holder) {mIsDrawing =false;}@Overridepublic void run() {long start = System.currentTimeMillis();while(mIsDrawing){draw();}long end = System.currentTimeMillis();if(end - start <100){try {Thread.sleep(100-(end - start));} catch (InterruptedException e) {e.printStackTrace();}}}private void draw(){try {canvas = mHolder.lockCanvas();canvas.drawColor(Color.WHITE);canvas.drawPath(mPath,paint);}catch (Exception e){}finally {if(canvas!=null){mHolder.unlockCanvasAndPost(canvas);}}}@Overridepublic boolean onTouchEvent(MotionEvent event) {int x = (int) event.getX();int y = (int) event.getY();switch (event.getAction()){case MotionEvent.ACTION_DOWN:mPath.moveTo(x,y);break;case MotionEvent.ACTION_MOVE:mPath.lineTo(x,y);break;case MotionEvent.ACTION_UP:break;}return true;}
}