Android绘图技巧使用详解

本文实例为大家分享了Android九宫格图片展示的具体代码，供大家参考，具体内容如下

XML绘图

Bitmap

<?xml version="1.0" encoding="utf-8"?>
<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
 android:src="@drawable/giao"/>

Shape

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
 android:shape="rectangle">
 <gradient
  android:startColor="#FF5DA2FF"
  android:endColor="#805FBBEF"
  android:angle="45"/>
 <padding
  android:bottom="7dp"
  android:top="7dp"
  android:left="7dp"
  android:right="7dp"/>
 <corners android:radius="8dp"/>
</shape>

Layer(实现Photoshop中类似图层的概念)

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
 <item android:drawable="@drawable/default_head"/>
 <item android:drawable="@drawable/default_head"
  android:left="10dip"
  android:right="10dip"
  android:top="10dip"
  android:bottom="10dip"/>
 <item android:drawable="@drawable/giao"
  android:left="200dp"
  android:right="200dp"
  android:top="200dp"
  android:bottom="200dp"/>
<!-- 图层效果-->
</layer-list>

Selector(帮助开发者实现静态绘图中的时间反馈)

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
 <item android:state_pressed="true">
  <shape android:shape="rectangle">
   <solid android:color="#33FD0000"/>
   <corners android:radius="5dp"/>
   <padding android:left="10dp"
    android:right="10dp"
    android:top="10dp"
    android:bottom="10dp"/>
  </shape>
 </item>
 <item>
  <shape android:shape="rectangle">
   <solid android:color="#ffffffff"/>
   <corners android:radius="5dp"/>
   <padding android:left="10dp"
    android:right="10dp"
    android:top="10dp"
    android:bottom="10dp"/>
  </shape>
 </item>
<!-- 点击反馈效果-->
</selector>

Android绘图技巧

Canvas(作为绘制图形的直接对象)

Canvas.save();

可以理解为保存画布，作用是将之前的所有已经绘制图像保存起来，让后续的操作就好像在一个新的图层上操作一样

Canvas.restore();

可以理解为Photoshop中的合并图层操作，作用是将save()之后绘制的所有的图像与save()之前的图像进行合并

Canvas.translate();

坐标系的平移

Canvas.rotate();

坐标系的旋转

Layer图层

特别注意的是 saveLayerAlpha()与restore()要同时使用，才能够在canvas 画出多个层次，就是花多少层就要有多少对两个函数！

@Override
 protected void onDraw(Canvas canvas) {
  //super.onDraw(canvas);
  drawLayer(canvas);
  //图层同样是基于栈的结构进行管理的
  @SuppressLint("DrawAllocation")
  Paint paint=new Paint();
  canvas.drawColor(Color.WHITE);
  paint.setColor(Color.BLUE);
  canvas.drawCircle(150,150,100,paint);

  canvas.saveLayerAlpha(0,0,400,400,127);//入栈(创建新图层)
  paint.setColor(Color.RED);
  canvas.drawCircle(200,200,100,paint);
  canvas.restore();//出栈
 }

像素点分析

bitmap.getPixels(pixels,offset,stride,x,y,width,height);

参数含义如下：

• pixels：接受位图颜色值的数组
• offset：写入到pixels[]中的第一个索引值
• stride：pixels[]的行间距
• x:从位图中读取的第一个像素的x坐标值
• y:从位图中读取的第一个像素的y坐标值
• width:每一行中读取的像素宽度
• height:读取的行数

画笔特效处理

PorterDuffXfermode

public class FilletView extends View {
 private Bitmap bitmap,out;
 private Paint paint;
 public FilletView(Context context) {
  super(context);
  inView();
 }

 public FilletView(Context context, @Nullable AttributeSet attrs) {
  super(context, attrs);
  inView();
 }

 public FilletView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  inView();
 }
 private void inView(){
  bitmap= BitmapFactory.decodeResource(getResources(), R.drawable.ask);
  out=Bitmap.createBitmap(bitmap.getWidth(),bitmap.getHeight(),Bitmap.Config.ARGB_8888);
  Canvas canvas=new Canvas(out);
  paint=new Paint();
  paint.setAntiAlias(true);
  canvas.drawRoundRect(0,0,bitmap.getWidth(),bitmap.getHeight(),80,80,paint);
  paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
  canvas.drawBitmap(bitmap,0,0,paint);
 }

 @Override
 protected void onDraw(Canvas canvas) {
  canvas.drawBitmap(out,0,0,null);

 }
}

Shader

• BitmapShader：位图Shader
• LinearGradient：线性Shader
• RadialGradient：光束Shader
• SweepGradient：梯度Shader
• ComposeShader：混合Shader

private void useBitmapShader(Canvas canvas){
  @SuppressLint("DrawAllocation")
  Bitmap bitmap= BitmapFactory.decodeResource(getResources(), R.drawable.default_head);
  @SuppressLint("DrawAllocation")
  BitmapShader shader=new BitmapShader(bitmap, Shader.TileMode.REPEAT,Shader.TileMode.REPEAT);
  @SuppressLint("DrawAllocation")
  Paint paint=new Paint();
  paint.setShader(shader);
  canvas.drawCircle(500,200,200,paint);
}

• Shader.TileMode.REPEAT：重复——横向、纵向不断重复
• Shader.TileMode.CLAMP：拉伸——拉伸的图片最后的那个像素，不断重复
• Shader.TileMode.MIRROR：镜像——横向不断翻转重复，横向不断翻转重复

PathEffect（各种笔触绘制一个路径）

• CornerPathEffect：拐角处变得圆滑
• DiscretePathEffect：线段上会产生许多杂点
• DashPathEffect：绘制虚线
• PathDashPathEffect：比DashPathEffect的功能更加强大，可以设置如方形点的虚线，圆形点的虚线。
• ComposePathEffect：组合任意两种PathEffect路径组合形成新的效果

public class PathEffectView extends View {
 private Paint paint;
 private Path mainPath;
 private PathEffect[] effects;
 public PathEffectView(Context context, @Nullable AttributeSet attrs) {
  super(context, attrs);
  inView();
 }
 private void inView(){
  paint=new Paint();
  paint.setStyle(Paint.Style.STROKE);
  paint.setStrokeWidth(5);
  paint.setColor(Color.DKGRAY);
  mainPath=new Path();
  mainPath.moveTo(0,0);
  for (int i = 0; i <= 30; i++) {
   mainPath.lineTo(i*35, (float) (Math.random()*100));
  }
  effects=new PathEffect[6];
 }

 @SuppressLint("DrawAllocation")
 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  effects[0]=null;
  effects[1]=new CornerPathEffect(30);
  effects[2]=new DiscretePathEffect(3,5);
  effects[3]=new DashPathEffect(new float[]{20,10,5,10},0);
  Path path=new Path();
  path.addRect(0,0,8,8,Path.Direction.CCW);
  effects[4]=new PathDashPathEffect(path,12,0,PathDashPathEffect.Style.ROTATE);
  effects[5]=new ComposePathEffect(effects[3],effects[1]);
  for (PathEffect effect : effects) {
   paint.setPathEffect(effect);
   canvas.drawPath(mainPath, paint);
   canvas.translate(0, 200);
  }
 }
}

SurfaceView

SurfaceView与View的区别：

1、View主要适用于主动更新的情况下，而SurfaceView主要适用于被动更新，例如频繁的更新
2、View在主线程中对画面进行更新，而SurfaceView通常会通过一个子线程来进行页面的刷新
3、View在绘图时没有使用双缓冲机制，而SurfaceView在底层机制中就已经实现了双缓冲机制

总结：SurfaceView适合需要频繁刷新，或者刷新时数据处理量比较大

public class SurfaceViewTemplate extends SurfaceView implements SurfaceHolder.Callback ,Runnable{
 //SurfaceHolder
 private SurfaceHolder holder;
 //用于绘画的Canvas
 private Canvas canvas;
 //子线程标志位
 private boolean isDrawing;
 private Paint paint;
 private Path path;
 private int x,y;
 public SurfaceViewTemplate(Context context) {
  super(context);
  inView();
 }

 public SurfaceViewTemplate(Context context, AttributeSet attrs) {
  super(context, attrs);
  inView();
 }

 public SurfaceViewTemplate(Context context, AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  inView();
 }
 private void inView(){
  holder=getHolder();
  holder.addCallback(this);
  setFocusable(false);//焦点
  setFocusableInTouchMode(true);
  this.setKeepScreenOn(true);
  path=new Path();
  paint=new Paint(Paint.ANTI_ALIAS_FLAG);
  paint.setColor(Color.RED);
  paint.setStyle(Paint.Style.STROKE);
  paint.setStrokeWidth(10);
  paint.setStrokeCap(Paint.Cap.ROUND);
  paint.setStrokeJoin(Paint.Join.ROUND);
 }
 @Override
 public void surfaceCreated(@NonNull SurfaceHolder surfaceHolder) {
  isDrawing=true;
  path.moveTo(0,400);
  new Thread(this).start();
 }

 @Override
 public void surfaceChanged(@NonNull SurfaceHolder surfaceHolder, int i, int i1, int i2) {

 }

 @Override
 public void surfaceDestroyed(@NonNull SurfaceHolder surfaceHolder) {
  isDrawing=false;
 }

 @Override
 public void run() {
  while (isDrawing){
   drawSome();
   x+=1;
   y= (int) (100*Math.sin(x*2*Math.PI/180)+400);
   path.lineTo(x,y);
  }
 }
 private void drawSome(){
  try {
   canvas=holder.lockCanvas();
   //draw something...
   canvas.drawColor(Color.WHITE);
   canvas.drawPath(path,paint);
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   if (canvas!=null){
    holder.unlockCanvasAndPost(canvas);
   }
  }

 }
}

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