Android 写一个带阴影的背景图 android绘制阴影

<!-- 阴影颜色 -->
<attr name="round_circle_shadowColor" format="color" />
<!-- 阴影水平偏移 -->
<attr name="round_circle_shadowOffsetX" format="dimension" />
<!-- 阴影垂直偏移 -->
<attr name="round_circle_shadowOffsetY" format="dimension" />

这里对属性的作用做了注释，很方便理解了。


接下来我们在基类中取出属性值

internal abstract class AbsRoundCirclePolicy(
 view: View,
 context: Context,
 attributeSet: AttributeSet?,
 attrs: IntArray,
 attrIndex: IntArray
 ) : IRoundCirclePolicy {

...
var mShadowSize = 0
var mShadowColor = 0
var mShadowOffsetX = 0
var mShadowOffsetY = 0

private fun initialize(context: Context, attributeSet: AttributeSet?, attrs: IntArray, attrIndexs: IntArray) {
    val typedArray = context.obtainStyledAttributes(attributeSet, attrs)

    ...

    mShadowSize = typedArray.getDimensionPixelSize(attrIndexs[9], 0)
    mShadowColor = typedArray.getColor(attrIndexs[10], 0x10000000)
    mShadowOffsetX = typedArray.getDimensionPixelSize(attrIndexs[11], 0)
    mShadowOffsetY = typedArray.getDimensionPixelSize(attrIndexs[12], 0)
}

然后我们在具体的策略裁剪类中拿到对应的值，内部我们需要在layout的时候去确定绘制内容的大小。

override fun onLayout(left: Int, top: Int, right: Int, bottom: Int) {
 setupRect()
 setupBG()
 setupShadow()
 }

先确定内容的大小，阴影的大小，再初始化绘制对象，初始化阴影对象

//设置Rect
 private fun setupRect() {
 val rectF = calculateBounds()
 val let: Float = rectF.left + mShadowSize
 val top: Float = rectF.top + mShadowSize
 val right: Float = rectF.right - mShadowSize
 val bottom: Float = rectF.bottom - mShadowSize

mDrawableRect.set(let, top, right, bottom)

//阴影的Rect
val shadowLet: Float
val shadowTop: Float
val shadowRight: Float
val shadowBottom: Float

if (mShadowOffsetX > 0) {
    shadowLet = let + mShadowOffsetX
    shadowRight = right
} else {
    shadowLet = let
    shadowRight = right + mShadowOffsetX
}

if (mShadowOffsetY > 0) {
    shadowTop = top + mShadowOffsetY
    shadowBottom = bottom
} else {
    shadowTop = top
    shadowBottom = bottom + mShadowOffsetY
}

mShadowRect.set(shadowLet, shadowTop, shadowRight, shadowBottom)

//设置画笔和BitmapShader等
 private fun setupBG() {

if (mRoundBackgroundDrawable != null && mRoundBackgroundBitmap != null) {

    mBitmapWidth = mRoundBackgroundBitmap!!.width
    mBitmapHeight = mRoundBackgroundBitmap!!.height

    mBitmapShader = BitmapShader(mRoundBackgroundBitmap!!, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP)

    if (mRoundBackgroundBitmap!!.width != 2) {
        updateShaderMatrix()
    }

    mBitmapPaint.isAntiAlias = true
    mBitmapPaint.shader = mBitmapShader

}

//阴影的设置与绘制准备
 private fun setupShadow() {
 if (mShadowSize > 0) {

mShadowPaint.color = Color.TRANSPARENT
    mShadowPaint.style = Paint.Style.STROKE
    mShadowPaint.strokeWidth = (mShadowSize / 4).toFloat()

    // 如果阴影不带透明度，强制给它设置一点透明度
    if (ColorUtils.setAlphaComponent(mShadowColor, 255) == mShadowColor) {
        mShadowColor = ColorUtils.setAlphaComponent(mShadowColor, 254)
    }
    mShadowPaint.color = mShadowColor

    mShadowPaint.maskFilter = BlurMaskFilter(mShadowSize / 1.2f, BlurMaskFilter.Blur.NORMAL)

} else {
    mShadowPaint.clearShadowLayer()
}

当我们全部的对象都初始化之后，总共是分两个步骤，一个是裁剪，一个是绘制，绘制又分背景内容的绘制和阴影的绘制。


在钩子函数中我们是在绘制完成之后再裁剪。

@TargetApi(Build.VERSION_CODES.LOLLIPOP)
 override fun beforeDispatchDraw(canvas: Canvas?) {
 //5.0版本以上，采用ViewOutlineProvider来裁剪view
 mContainer.clipToOutline = true
 }

@TargetApi(Build.VERSION_CODES.LOLLIPOP)
override fun afterDispatchDraw(canvas: Canvas?) {
    //5.0版本以上，采用ViewOutlineProvider来裁剪view
    mContainer.outlineProvider = object : ViewOutlineProvider() {
        override fun getOutline(view: View, outline: Outline) {

            if (isCircleType) {
                //如果是圆形裁剪圆形
                val bounds = Rect()
                calculateBounds().roundOut(bounds)
                outline.setRoundRect(bounds, bounds.width() / 2.0f)

            } else {
                //如果是圆角-裁剪圆角
                if (mTopLeft > 0 || mTopRight > 0 || mBottomLeft > 0 || mBottomRight > 0) {
                    //如果是单独的圆角
                    val path = Path()
                    path.addRoundRect(
                        calculateBounds(),
                        floatArrayOf(mTopLeft, mTopLeft, mTopRight, mTopRight, mBottomRight, mBottomRight, mBottomLeft, mBottomLeft),
                        Path.Direction.CCW
                    )

                    //不支持2阶的曲线
                    outline.setConvexPath(path)

                } else {
                    //如果是统一圆角
                    outline.setRoundRect(0, 0, mContainer.width, mContainer.height, mRoundRadius)
                }

            }
        }
    }
}

而绘制则是在我们onDraw的钩子函数中实现，需要注意的是我们需要先绘制阴影再绘制内容，这样才能实现阴影在底部的效果。

override fun onDraw(canvas: Canvas?): Boolean {
 if (isCircleType) {

if (mShadowSize > 0) {
            //阴影的绘制
            canvas?.drawOval(mShadowRect, mShadowPaint)
        }

        //绘制圆角背景图
        canvas?.drawCircle(
            mDrawableRect.centerX(), mDrawableRect.centerY(),
            Math.min(mDrawableRect.height() / 2.0f, mDrawableRect.width() / 2.0f), mBitmapPaint
        )

    } else {
        //自定义圆角
        if (mTopLeft > 0 || mTopRight > 0 || mBottomLeft > 0 || mBottomRight > 0) {

            if (mShadowSize > 0) {
                //阴影的绘制
                mShadowPath.reset()
                mShadowPath.addRoundRect(
                    mShadowRect, floatArrayOf(mTopLeft, mTopLeft, mTopRight, mTopRight, mBottomRight, mBottomRight, mBottomLeft, mBottomLeft),
                    Path.Direction.CW
                )
                canvas?.drawPath(mShadowPath, mShadowPaint)
            }

            //使用单独的圆角背景