Android阴影简单实现

:)

**V~**

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阴影绘制需要的知识点

• 硬件加速
• Paint对象的setShadowLayer方法

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android硬件加速

• Application级别开启硬件加速

<application android:hardwareAccelerated="true"/>

• Activity级别开启硬件加速

<activity android:hardwareAccelerated="true">

• Window级别开启硬件加速

getWindow().setFlags( 
   WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED,
    WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED
);

• View级别开启硬件加速
  myView.setLayerType(View.LAYER_TYPE_*, null);

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setShadowLayer

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思路来自一个开源库

https://github.com/yingLanNull/ShadowImageView

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解析上面那个开源库

• 这个库的主要代码就一个自定义的控件ShadowImageView(继承RelativeLayout)

public class ShadowImageView extends RelativeLayout

• 实现思路就是先给这个控件绘制一个带阴影的背景，然后在给这个控件添加一个ImageView的子控件
• 构造方法的实现

public ShadowImageView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setPadding(80, 40, 80, 120); //设置一个padding用来绘制阴影背景
        setGravity(Gravity.CENTER);
        setLayerType(LAYER_TYPE_SOFTWARE, null); //开启硬件加速
        
        //添加一个imageView的子控件
        RoundImageView roundImageView = new RoundImageView(context);
        roundImageView.setScaleType(ImageView.ScaleType.FIT_XY);
        if (imageresource == -1) {
            roundImageView.setImageResource(android.R.color.transparent);
        } else {
            roundImageView.setImageResource(imageresource);
        }

        addView(roundImageView);
    }

• 背景的绘制方法dispatchDraw（简化）

@Override
protected void dispatchDraw(Canvas canvas) {
            //初始化一个绘制背景的画笔
            Paint shadowPaint = new Paint();
            shadowPaint.setColor(Color.WHITE);
            shadowPaint.setStyle(Paint.Style.FILL);
            shadowPaint.setAntiAlias(true);
           //计算阴影的偏移量 和 给画笔设置阴影
            int radius = view.getHeight() / 12 > 40 ? 40 : view.getHeight() / 12;
            int shadowColor = view.getHeight() / 16 > 28 ? 28 : view.getHeight() / 16;
            shadowPaint.setShadowLayer(radius, 0, shadowColor, getDarkerColor(rgb));

             //确定阴影的的整个大小
            RectF rectF = new RectF(view.getX() + (view.getWidth() / 20), view.getY(), view.getX() + view.getWidth() - (view.getWidth() / 20), view.getY() + view.getHeight() - ((view.getHeight() / 40)));
            canvas.drawRoundRect(rectF, shadowRound, shadowRound, shadowPaint);
            canvas.save();
            super.dispatchDraw(canvas);
}

• 阴影颜色的获取（上面使用的是getDarkerColor方法，这里面有一个小技巧就是HSV模型）

    public int getDarkerColor(int color) {
        float[] hsv = new float[3];
        Color.colorToHSV(color, hsv);
        hsv[1] = hsv[1] + 0.1f;
        hsv[2] = hsv[2] - 0.1f;
        int darkerColor = Color.HSVToColor(hsv);
        return darkerColor;
    }

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简单说一下HSV

• 平时我们说颜色一般都是RGB，R分量表示红色，G绿色，、B蓝色
• 而HSV也是用来表示颜色的，只是H表示色调（0 ~ 360），S表示饱和度（0 ~ 1），V表示明度（0 ~ 1）

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