Android 高級UI 目錄
Paint 畫筆的高級技能
渲染 Shader:
BitmapShader位圖的圖象渲染器
LinearGradient線性渲染
RadialGradient環(huán)形渲染
SweepGradient梯度渲染（掃描渲染）
ComposeShader組合渲染

可以繪制圖片、顏色塊、文字
canvas.drawCircle()
canvas.drawRect()
canvas.drawOval()

public class LinearGradientTextView extends android.support.v7.widget.AppCompatTextView {


   private TextPaint paint;

   private LinearGradient linearGradient;

   private Matrix matrix;

   private float translateX;

   private float deltaX = 20;

   public LinearGradientTextView(Context context) {
       super(context);
   }

   public LinearGradientTextView(Context context,
           @Nullable AttributeSet attrs) {
       super(context, attrs);

   }


   @Override
   protected void onSizeChanged(int w, int h, int oldw, int oldh) {
       super.onSizeChanged(w, h, oldw, oldh);

       paint = getPaint();
       //GradientSize=兩個文字的大小
       String text = getText().toString();
       float textWidth = paint.measureText(text);
       int gradientSize = (int) (3 * textWidth / text.length());
       linearGradient = new LinearGradient(-gradientSize, 0, 0, 0,
               new int[]{0x22ffffff, 0xffffffff, 0x22ffffff},
               new float[]{0, 0.5f, 1}, TileMode.CLAMP);//邊緣融合
       paint.setShader(linearGradient);
       matrix = new Matrix();
   }

   @Override
   protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
       float textWidth = getPaint().measureText(getText().toString());
       translateX += deltaX;
       if(translateX > textWidth + 1|| translateX < 1){
           deltaX = -deltaX;
       }
//      matrix.setScale(sx, sy)
       //動畫平移
       matrix.setTranslate(translateX, 0);
       linearGradient.setLocalMatrix(matrix);

       postInvalidateDelayed(50);

   }
}

public class MyGradientView extends View {

    private Bitmap bitmap;

    private Paint paint;

    private BitmapShader bitmapShader;

    private int width;
    private int height;
    private int[] colors = {Color.RED, Color.GREEN, Color.BLUE, Color.YELLOW};

    private RadialGradient radialGradient;

    private SweepGradient sweepGradient;

    //組合渲染
    private ComposeShader composeShader;

    public MyGradientView(Context context) {
        super(context);

        bitmap = ((BitmapDrawable) getResources().getDrawable(R.drawable.fengjing)).getBitmap();

        paint = new Paint();

        width = bitmap.getWidth();
        height = bitmap.getHeight();
    }

    public MyGradientView(Context context,
            @Nullable AttributeSet attrs,
            Bitmap bitmap) {
        super(context, attrs);
        this.bitmap = bitmap;
    }

    public MyGradientView(Context context,
            @Nullable AttributeSet attrs, int defStyleAttr,
            Bitmap bitmap) {
        super(context, attrs, defStyleAttr);
        this.bitmap = bitmap;

    }

    /**
     *
     * @param canvas
     */
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawColor(Color.WHITE);
        //canvas.drawBitmap(bitmap, 0, 0, paint);
        /**
         * TileMode.CLAMP 拉伸最后一個像素去鋪滿剩下的地方
         * TileMode.MIRROR 通過鏡像翻轉(zhuǎn)鋪滿剩下的地方
         * TileMode.REPEAT 重復圖片填充整個畫面(電腦設置壁紙)
         */
        bitmapShader = new BitmapShader(bitmap, TileMode.REPEAT, TileMode.REPEAT);
        //   bitmapShader = new BitmapShader(bitmap, TileMode.CLAMP, TileMode.CLAMP);
        paint.setShader(bitmapShader);
        paint.setAntiAlias(true);

        //canvas.drawRect(new Rect(0, 0, 800, 800), paint);

        //設置像素矩陣，來調(diào)整大小，為了解決寬高不一致的問題
//        float scale = Math.max(width, height) * 1.0f / Math.min(width, height);
//        Matrix matrix = new Matrix();
//        matrix.setScale(scale, scale);//縮放比例
//        bitmapShader.setLocalMatrix(matrix);

        //  canvas.drawRect(new Rect(0, 0, 800, 800), paint);
        //canvas.drawCircle(width/2,width/2, width/2,paint);

        //     canvas.drawCircle(Math.max(width, height) / 2f,
        //         scale * Math.max(width, height) / 2f, Math.max(width, height) / 2f, paint);

        //canvas.drawOval(new RectF(0, 0, width, height * 1.5f), paint);
        // canvas.drawOval(new RectF(0,0,width,width),paint);

        //通過shapeDrawable也可以實現(xiàn)
//        ShapeDrawable shapeDrawable =new ShapeDrawable(new OvalShape());
//        shapeDrawable.getPaint().setShader(bitmapShader);
//        shapeDrawable.setBounds(0,0,width,width);
//        shapeDrawable.draw(canvas);
        /**
         * 線性漸變
         * x0，y0 起始點
         * x1，y1 結(jié)束點
         * int[] colors 中間依次要出現(xiàn)的顏色
         * float[] positions 數(shù)組大小跟colors數(shù)組一樣大，中間依次擺放的幾個顏色分別放置在那個位置上(參考比例從左往右)
         * title
         *
         */
//        LinearGradient linearGradient = new LinearGradient(0, 0, 400, 400, colors, null,
//                TileMode.REPEAT);
//        paint.setShader(linearGradient);
//        canvas.drawRect(0,0,400,400,paint);

//        //環(huán)形渲染
//        radialGradient = new RadialGradient(300,300,100,colors,null,TileMode.REPEAT);
//        paint.setShader(radialGradient);
//        canvas.drawCircle(300,300,300,paint);

        //梯度渲染
//        sweepGradient = new SweepGradient(300, 300, colors, null);
//        paint.setShader(sweepGradient);
//        canvas.drawCircle(300, 300, 300, paint);

        //組合渲染
        LinearGradient linearGradient = new LinearGradient(0, 0, 400, 400, colors, null,
                TileMode.REPEAT);
        composeShader = new ComposeShader(linearGradient, bitmapShader, PorterDuff.Mode.SRC_OVER);
        paint.setShader(composeShader);
        canvas.drawRect(0, 0, 800, 1000, paint);
    }
}

public class ZoomImageView extends View {

    //放大倍數(shù)
    private static final int FACTOR = 3;
    private static final int RADIUS = 100;
    public Bitmap bitmap;
    private ShapeDrawable drawable;

    private Matrix matrix = new Matrix();

    public ZoomImageView(Context context) {
        super(context);
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.beauty);
        Bitmap bmp = bitmap;
        bmp = Bitmap
                .createScaledBitmap(bmp, bmp.getWidth() * FACTOR, bmp.getHeight() * FACTOR, true);

        //制作一個圓形的圖片(放大的局部)，蓋在canvas上
        BitmapShader shader = new BitmapShader(bmp, TileMode.CLAMP, TileMode.CLAMP);
        drawable = new ShapeDrawable(new OvalShape());
        drawable.getPaint().setShader(shader);
        //切出矩形區(qū)域----用于繪制圓（內(nèi)切圓）
        drawable.setBounds(0, 0, RADIUS * 2, RADIUS * 2);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawBitmap(bitmap, 0, 0, null);
        //畫制作好的圓形圖片
        drawable.draw(canvas);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        int x = (int) event.getX();
        int y = (int) event.getY();

        matrix.setTranslate(RADIUS - x * FACTOR, RADIUS - y * FACTOR);
        drawable.getPaint().getShader().setLocalMatrix(matrix);
        drawable.setBounds(x - RADIUS, y - RADIUS, x + RADIUS, y + RADIUS);
        //手指按下才進行縮放
        postInvalidate();
        return super.onTouchEvent(event);
    }
}