Android gallery 3D效果

转载来自:Http://blog.csdn.net/leehong2005/article/details/8070538  

在看了iOS上面的CoverFlow后，感觉效果真的不错，就想在Android上面实现一个，这个程序在网上参考了一此核心的代码，当然我添加了一些其他的东西，废话不多说，先看效果，不然就是无图无真相。

其实实现这个效果很简单，下面作一个简单的介绍

一，创建倒影效果

这个基本思路是：

1.创建一个源图一样的图，利用martrix将图片旋转180度。这个倒影图的高是源图的一半。

Matrix matrix = new Matrix();
// 1表示放大比例，不放大也不缩小。
// -1表示在y轴上相反，即旋转180度。
matrix.preScale(1, -1);
Bitmap reflectionBitmap = Bitmap.createBitmap(
    srcBitmap,
    0,
    srcBitmap.getHeight() / 2,  // top为源图的一半
    srcBitmap.getWidth(),       // 宽度与源图一样
    srcBitmap.getHeight() / 2,  // 高度与源图的一半
    matrix,
    false);

2，创建一个最终效果的图，即源图 + 间隙 + 倒影。

final int REFLECTION_GAP = 5;
Bitmap bitmapWithReflection = Bitmap.createBitmap(
       reflectionWidth,
       srcHeight + reflectionHeight + REFLECTION_GAP,
       Config.ARGB_8888);

3，依次将源图、倒影图绘制在最终的bitmap上面。

// Prepare the canvas to draw stuff.
Canvas canvas = new Canvas(bitmapWithReflection);
                                                                        
// Draw the original bitmap.
canvas.drawBitmap(srcBitmap, 0, 0, null);
                                                                        
// Draw the reflection bitmap.
canvas.drawBitmap(reflectionBitmap, 0, srcHeight + REFLECTION_GAP, null);

4，创建LinearGradient，从而给定一个由上到下的渐变色。

Paint paint = new Paint();
paint.setAntiAlias(true);
LinearGradient shader = new LinearGradient(
        0,
        srcHeight,
        0,
        bitmapWithReflection.getHeight() + REFLECTION_GAP,
        0x70FFFFFF,
        0x00FFFFFF,
        TileMode.MIRROR);
paint.setShader(shader);
paint.setXfermode(new PorterDuffXfermode(android.graphics.PorterDuff.Mode.DST_IN));
// Draw the linear shader.
canvas.drawRect(
        0,
        srcHeight,
        srcWidth,
        bitmapWithReflection.getHeight() + REFLECTION_GAP,
        paint);

二，扩展Gallery

扩展系统的gallery，我们需要重写两个方法，getChildStaticTransfORMation()和getChildDrawinGorder()，同时，要使这两个方法能被调用，必须执行如下两行代码，文档上面是有说明的。

// Enable set transformation.
this.setStaticTransformationsEnabled(true);
// Enable set the children drawing order.
this.setChildrenDrawingOrderEnabled(true);

• getChildDrawingOrder的实现

@Override
protected int getChildDrawingOrder(int childCount, int i)
{
    // Current selected index.
    int selectedIndex = getSelectedItemPosition() - getFirstVisiblePosition();
    if (selectedIndex < 0)
    {
        return i;
    }
                                        
    if (i < selectedIndex)
    {
        return i;
    }
    else if (i >= selectedIndex)
    {
        return childCount - 1 - i + selectedIndex;
    }
    else
    {
        return i;
    }
}

这里为什么要计算drawing order，因为从上图中看到，我们的效果是：中间左边的顺序是 0， 1， 2，右边的child覆盖左边的child，而在中间右边的顺序正好相反，左边的覆盖右边的，所以我们要重写这个方法，而gallery自身的实现，不是这种效果。

• getChildStaticTransformation的实现

@Override
protected boolean getChildStaticTransformation(View child, Transformation t)
{
    super.getChildStaticTransformation(child, t);
                               
    final int childCenter = getCenterOfView(child);
    final int childWidth  = child.getWidth();
                               
    int rotationAngle = 0;
    t.clear();
    t.setTransformationType(Transformation.TYPE_MATRIX);
                               
    // If the child is in the center, we do not rotate it.
    if (childCenter == mCoveflowCenter)
    {
        transformImageBitmap(child, t, 0);
    }
    else
    {
        // Calculate the rotation angle.
        rotationAngle = (int)(((float)(mCoveflowCenter - childCenter) / childWidth) * mMaxRotationAngle);
                                   
        // Make the angle is not bigger than maximum.
        if (Math.abs(rotationAngle) > mMaxRotationAngle)
        {
            rotationAngle = (rotationAngle < 0) ? -mMaxRotationAngle : mMaxRotationAngle;
        }
                                   
        transformImageBitmap(child, t, rotationAngle);
    }
                               
    return true;
}

这个方法就是根据child来计算它的transformation（变换），我们需要去修改它里面的matrix，从而达到旋转的效果。根据位置和角度来计算的matrix的方法写在另外一个方法transformImageBitmap中实现。

• transformImageBitmap()的实现

private void transformImageBitmap(View child, Transformation t, int rotationAngle)
{
    mCamera.save();
                      
    final Matrix p_w_picpathMatrix = t.getMatrix();
    final int p_w_picpathHeight = child.getHeight();
    final int p_w_picpathWidth  = child.getWidth();
    final int rotation    = Math.abs(rotationAngle);
                      
    // Zoom on Z axis.
    mCamera.translate(0, 0, mMaxZoom);
                      
    if (rotation < mMaxRotationAngle)
    {
        float zoomAmount = (float)(mMaxZoom + rotation * 1.5f);
        mCamera.translate(0, 0, zoomAmount);
    }
                      
    // Rotate the camera on Y axis.
    mCamera.rotateY(rotationAngle);
    // Get the matrix from the camera, in fact, the matrix is S (scale) transformation.
    mCamera.getMatrix(p_w_picpathMatrix);
                      
    // The matrix final is T2 * S * T1, first translate the center point to (0, 0),
    // then scale, and then translate the center point to its original point.
    // T * S * T
                      
    // S * T1
    p_w_picpathMatrix.postTranslate((p_w_picpathWidth / 2), (p_w_picpathHeight / 2));
    // (T2 * S) * T1
    p_w_picpathMatrix.preTranslate(-(p_w_picpathWidth / 2), -(p_w_picpathHeight / 2));
                      
    mCamera.restore();
}

这里，简单说明一个，

       第一，先在Z轴上平称，其实就是得到一个缩放矩阵变换，我这里简写为 S。

       第二，是利用camera这个类来生成matrix，其实mCamera.rotateY就是围绕Y轴旋转。这里生成了一个旋转矩阵，记为 R 。经过这两步，此时调用mCamera.getMatrix(p_w_picpathMatrix); 从Camera中得到matrix，此时这个矩阵中包含了S * R。

       第三，最关键是下面两句      

// S * T1
 p_w_picpathMatrix.postTranslate((p_w_picpathWidth / 2), (p_w_picpathHeight / 2));
 // (T2 * S) * T1
 p_w_picpathMatrix.preTranslate(-(p_w_picpathWidth / 2), -(p_w_picpathHeight / 2));

于这里涉及到旋转与缩放，缩放操作其实应该是针对Child中点进行了，这里就是作一个平衡操作，我们必须是先平移，再缩放，再平移回原来位置，所以，我们最终的矩阵变换应该是这样的：

       M = T * （S * R） * T1   （这里在T1表示与T相反）。

三，完整代码

GalleryFlow.java

import android.content.Context;
import android.graphics.Camera;
import android.graphics.Matrix;
import android.util.AttributeSet;
import android.view.View;
import android.view.animation.Transformation;
import android.widget.Gallery;
public class GalleryFlow extends Gallery
{
    
    private Camera mCamera = new Camera();
          
    
    private int mMaxRotationAngle = 60;
          
    
    private int mMaxZoom = -120;
          
    
    private int mCoveflowCenter = 0;
          
    public GalleryFlow(Context context)
    {
        this(context, null);
    }
          
    public GalleryFlow(Context context, AttributeSet attrs)
    {
        this(context, attrs, 0);
    }
          
    public GalleryFlow(Context context, AttributeSet attrs, int defStyle)
    {
        super(context, attrs, defStyle);
              
        // Enable set transformation.
        this.setStaticTransformationsEnabled(true);
        // Enable set the children drawing order.
        this.setChildrenDrawingOrderEnabled(true);
    }
          
    public int getMaxRotationAngle()
    {
        return mMaxRotationAngle;
    }
          
    public void setMaxRotationAngle(int maxRotationAngle)
    {
        mMaxRotationAngle = maxRotationAngle;
    }
          
    public int getMaxZoom()
    {
        return mMaxZoom;
    }
          
    public void setMaxZoom(int maxZoom)
    {
        mMaxZoom = maxZoom;
    }
          
    @Override
    protected int getChildDrawingOrder(int childCount, int i)
    {
        // Current selected index.
        int selectedIndex = getSelectedItemPosition() - getFirstVisiblePosition();
        if (selectedIndex < 0)
        {
            return i;
        }
              
        if (i < selectedIndex)
        {
            return i;
        }
        else if (i >= selectedIndex)
        {
            return childCount - 1 - i + selectedIndex;
        }
        else
        {
            return i;
        }
    }
          
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh)
    {
        mCoveflowCenter = getCenterOfCoverflow();
        super.onSizeChanged(w, h, oldw, oldh);
    }
          
    private int getCenterOfView(View view)
    {
        return view.getLeft() + view.getWidth() / 2;
    }
          
    @Override
    protected boolean getChildStaticTransformation(View child, Transformation t)
    {
        super.getChildStaticTransformation(child, t);
              
        final int childCenter = getCenterOfView(child);
        final int childWidth  = child.getWidth();
              
        int rotationAngle = 0;
        t.clear();
        t.setTransformationType(Transformation.TYPE_MATRIX);
              
        // If the child is in the center, we do not rotate it.
        if (childCenter == mCoveflowCenter)
        {
            transformImageBitmap(child, t, 0);
        }
        else
        {
            // Calculate the rotation angle.
            rotationAngle = (int)(((float)(mCoveflowCenter - childCenter) / childWidth) * mMaxRotationAngle);
                  
            // Make the angle is not bigger than maximum.
            if (Math.abs(rotationAngle) > mMaxRotationAngle)
            {
                rotationAngle = (rotationAngle < 0) ? -mMaxRotationAngle : mMaxRotationAngle;
            }
                  
            transformImageBitmap(child, t, rotationAngle);
        }
              
        return true;
    }
          
    private int getCenterOfCoverflow()
    {
        return (getWidth() - getPaddingLeft() - getPaddingRight()) / 2 + getPaddingLeft();
    }
          
    private void transformImageBitmap(View child, Transformation t, int rotationAngle)
    {
        mCamera.save();
              
        final Matrix p_w_picpathMatrix = t.getMatrix();
        final int p_w_picpathHeight = child.getHeight();
        final int p_w_picpathWidth  = child.getWidth();
        final int rotation    = Math.abs(rotationAngle);
              
        // Zoom on Z axis.
        mCamera.translate(0, 0, mMaxZoom);
              
        if (rotation < mMaxRotationAngle)
        {
            float zoomAmount = (float)(mMaxZoom + rotation * 1.5f);
            mCamera.translate(0, 0, zoomAmount);
        }
              
        // Rotate the camera on Y axis.
        mCamera.rotateY(rotationAngle);
        // Get the matrix from the camera, in fact, the matrix is S (scale) transformation.
        mCamera.getMatrix(p_w_picpathMatrix);
              
        // The matrix final is T2 * S * T1, first translate the center point to (0, 0),
        // then scale, and then translate the center point to its original point.
        // T * S * T
              
        // S * T1
        p_w_picpathMatrix.postTranslate((p_w_picpathWidth / 2), (p_w_picpathHeight / 2));
        // (T2 * S) * T1
        p_w_picpathMatrix.preTranslate(-(p_w_picpathWidth / 2), -(p_w_picpathHeight / 2));
              
        mCamera.restore();
    }
}

BitmapUtil.java

package com.lee.gallery3D.utils;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.LinearGradient;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PixelFormat;
import android.graphics.PorterDuffXfermode;
import android.graphics.Shader.TileMode;
import android.graphics.drawable.Drawable;
public class BitmapUtil
{
    public static Bitmap createReflectedBitmap(Bitmap srcBitmap)
    {
        if (null == srcBitmap)
        {
            return null;
        }
          
        // The gap between the reflection bitmap and original bitmap.
        final int REFLECTION_GAP = 4;
          
        int srcWidth  = srcBitmap.getWidth();
        int srcHeight = srcBitmap.getHeight();
        int reflectionWidth  = srcBitmap.getWidth();
        int reflectionHeight = srcBitmap.getHeight() / 2;
          
        if (0 == srcWidth || srcHeight == 0)
        {
            return null;
        }
          
        // The matrix
        Matrix matrix = new Matrix();
        matrix.preScale(1, -1);
          
        try
        {
            // The reflection bitmap, width is same with original's, height is half of original's.
            Bitmap reflectionBitmap = Bitmap.createBitmap(
                    srcBitmap,
                    0,
                    srcHeight / 2,
                    srcWidth,
                    srcHeight / 2,
                    matrix,
                    false);
              
            if (null == reflectionBitmap)
            {
                return null;
            }
              
            // Create the bitmap which contains original and reflection bitmap.
            Bitmap bitmapWithReflection = Bitmap.createBitmap(
                    reflectionWidth,
                    srcHeight + reflectionHeight + REFLECTION_GAP,
                    Config.ARGB_8888);
              
            if (null == bitmapWithReflection)
            {
                return null;
            }
              
            // Prepare the canvas to draw stuff.
            Canvas canvas = new Canvas(bitmapWithReflection);
              
            // Draw the original bitmap.
            canvas.drawBitmap(srcBitmap, 0, 0, null);
              
            // Draw the reflection bitmap.
            canvas.drawBitmap(reflectionBitmap, 0, srcHeight + REFLECTION_GAP, null);
              
            Paint paint = new Paint();
            paint.setAntiAlias(true);
            LinearGradient shader = new LinearGradient(
                    0,
                    srcHeight,
                    0,
                    bitmapWithReflection.getHeight() + REFLECTION_GAP,
                    0x70FFFFFF,
                    0x00FFFFFF,
                    TileMode.MIRROR);
            paint.setShader(shader);
            paint.setXfermode(new PorterDuffXfermode(android.graphics.PorterDuff.Mode.DST_IN));
              
            // Draw the linear shader.
            canvas.drawRect(
                    0,
                    srcHeight,
                    srcWidth,
                    bitmapWithReflection.getHeight() + REFLECTION_GAP,
                    paint);
              
            return bitmapWithReflection;
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
          
        return null;
    }
}