Android動畫之圖片吸入動畫詳解

1，背景

吸入(Inhale)效果，最初我是在iOS上面看到的，它是在Note程序中，用戶可能添加了一頁記錄，在做刪除時，它的刪除效果是：這一頁內容吸入到一個垃圾框的圖標裏面。請看下圖所示：

這裏，我要介紹的是如何在Android上面實現一個類似的效果。先看看我實現的效果圖。

上圖演示了動畫的某幾幀，其中從1 - 4，演示了圖片從原始圖形吸入到一個點（紅色標識）。

實現這樣的效果，我們利用了Canvas.drawBitmapMesh()方法，這裏涉及到了一個Mesh的概念。

2，Mesh的概念

Mesh表示網格，說得通俗一點，可以將畫板想像成一張格子布，在這個張布上繪製圖片。對於一個網格端點均勻分佈的網格來說，橫向有meshWidth + 1個頂點，縱向有meshHeight + 1個端點。頂點數據verts是以行優先的數組（二維數組以一維數組表示，先行後列）。網格可以不均勻分佈。請看下圖所示： 

上圖中顯示了把圖片分成很多格子，上圖中的每個格子是均勻的，它的頂點數是：(meshWidth + 1) * (meshHeight + 1)個，那麼放這些頂點的一維數據的大小應該是：(meshWidth + 1) * (meshHeight + 1) * 2 (一個點包含x, y座標)

float[] vertices = new float[：(meshWidth + 1) * (meshHeight + 1) * 2];

試想，我們讓這個格子(mesh)不均勻分佈，那麼繪製出來的圖片就會變形，請看下圖所示：

3，如何構建Mesh

吸入動畫的核心是吸入到一個點，那麼我們就是要在不同的時刻構造出不同的mesh的頂點座標，我們是怎麼做的呢？

3.1，創建兩條路徑(Path)

假如我們的吸入效果是從上到下吸入，我們構造的Path是如下圖所示：

上圖中藍色的線表示我們構造的Path，其實只要我們沿着這兩條Path來構造mesh頂點就可以了。

構建兩條Path的代碼如下：

mFirstPathMeasure.setPath(mFirstPath, false);
mSecondPathMeasure.setPath(mSecondPath, false);
float w = mBmpWidth;
float h = mBmpHeight;
mFirstPath.reset();
mSecondPath.reset();
mFirstPath.moveTo(0, 0);
mSecondPath.moveTo(w, 0);
mFirstPath.lineTo(0, h);
mSecondPath.lineTo(w, h);
mFirstPath.quadTo(0, (endY + h) / 2, endX, endY);
mSecondPath.quadTo(w, (endY + h) / 2, endX, endY);

3.2，根據Path來計算頂點座標

算法：

1，假如我們把格子分爲WIDTH, HEIGHT份，把Path的長度分的20份，[0， length]，表示20個時刻。

2，第0時間，我們要的形狀是一個矩形，第1時刻可能是梯形，第n時間可能是一個三角形。下圖說明了動畫過程中圖片的變化。

3，第一條（左）Path的長度爲len1，第二條（右）Path的長度爲len2，對於任意時刻 t [0 - 20]，我們可以知道梯形的四個頂點距Path最頂端的length。

左上角：t * (len1 / 20)
左下角：t * (len1 / 20) + bitmapHeight
右上角：t * (len2 / 20)
右下角：t * (len2 / 20) + bitmapHeight 

我們可以通過PathMeasure類根據length算出在Path上面點的座標，也就是說，根據兩條Path，我們可以分別算了四個頂點的座標，我這裏分別叫做A, B, C, D（順時針方向），有了點的座標，我們可以算出AD，BC的長度，並且將基進行HEIGHT等分（因爲我們把mesh分成寬WIDTH，高HEIGHT等分），將AD，BC上面每等分的點連接起來形成一條直接，將再這條直接水平WIDTH等分，根據直線方程，依據x算出y，從而算出每一個頂點的座標。（請參考上圖）

下面是計算頂點座標的詳細代碼： 

private void buildMeshByPathOnVertical(int timeIndex)
{
    mFirstPathMeasure.setPath(mFirstPath, false);
    mSecondPathMeasure.setPath(mSecondPath, false);
    int index = 0;
    float[] pos1 = {0.0f, 0.0f};
    float[] pos2 = {0.0f, 0.0f};
    float firstLen  = mFirstPathMeasure.getLength();
    float secondLen = mSecondPathMeasure.getLength();
    float len1 = firstLen / HEIGHT;
    float len2 = secondLen / HEIGHT;
    float firstPointDist  = timeIndex * len1;
    float secondPointDist = timeIndex * len2;
    float height = mBmpHeight;
    mFirstPathMeasure.getPosTan(firstPointDist, pos1, null);
    mFirstPathMeasure.getPosTan(firstPointDist + height, pos2, null);
    float x1 = pos1[0];
    float x2 = pos2[0];
    float y1 = pos1[1];
    float y2 = pos2[1];
    float FIRST_DIST  = (float)Math.sqrt( (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) );
    float FIRST_H = FIRST_DIST / HEIGHT;
    mSecondPathMeasure.getPosTan(secondPointDist, pos1, null);
    mSecondPathMeasure.getPosTan(secondPointDist + height, pos2, null);
    x1 = pos1[0];
    x2 = pos2[0];
    y1 = pos1[1];
    y2 = pos2[1];
    float SECOND_DIST = (float)Math.sqrt( (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) );
    float SECOND_H = SECOND_DIST / HEIGHT;
    for (int y = 0; y <= HEIGHT; ++y)
    {
        mFirstPathMeasure.getPosTan(y * FIRST_H + firstPointDist, pos1, null);
        mSecondPathMeasure.getPosTan(y * SECOND_H + secondPointDist, pos2, null);
        float w = pos2[0] - pos1[0];
        float fx1 = pos1[0];
        float fx2 = pos2[0];
        float fy1 = pos1[1];
        float fy2 = pos2[1];
        float dy = fy2 - fy1;
        float dx = fx2 - fx1;
        for (int x = 0; x <= WIDTH; ++x)
        {
            // y = x * dy / dx
            float fx = x * w / WIDTH;
            float fy = fx * dy / dx;
            mVerts[index * 2 + 0] = fx + fx1;
            mVerts[index * 2 + 1] = fy + fy1;
            index += 1;
        }
    }
}

4，如何繪製

繪製代碼很簡單，調用Canvas.drawBitmapMesh方法。最本質是要計算出一個頂點數組。

canvas.drawBitmapMesh(mBitmap,
        mInhaleMesh.getWidth(),
        mInhaleMesh.getHeight(),
        mInhaleMesh.getVertices(),
        0, null, 0, mPaint);

5，如何實現動畫

protected void applyTransformation(float interpolatedTime, Transformation t)
        {
            int curIndex = 0;
            Interpolator interpolator = this.getInterpolator();
            if (null != interpolator)
            {
                float value = interpolator.getInterpolation(interpolatedTime);
                interpolatedTime = value;
            }
            if (mReverse)
            {
                interpolatedTime = 1.0f - interpolatedTime;
            }
            curIndex = (int)(mFromIndex + (mEndIndex - mFromIndex) * interpolatedTime);
            if (null != mListener)
            {
                mListener.onAnimUpdate(curIndex);
            }
        }

在動畫裏面，我們計算出要做動畫的幀的index，假設我們把吸入動畫分爲20幀，在動畫裏面，計算出每一幀，最後通過onAnimUpdate(int index)方法回調，在這個方法實現裏面，我們根據幀的index來重新計算一個新的mesh頂點數組，再用這個數組來繪製bitmap。這樣，我們就可以看來一組連續變化的mesh，也就能看到吸擴效果的動畫。

6，總結

本文簡單介紹了吸放效果的實現，根據這個原理，我們可以構造更加複雜的Path來做更多的效果。同時，也能實現向上，向左，向右的吸入效果。

最本質是我們要理解Mesh的概念，最核心的工作就是構造出Mesh的頂點座標。

計算Mesh通常是一個很複雜的工作，作一些簡單的變形還可以，對於太複雜的變形，可能還是不太方便。另外，像書籍翻頁的效果，用mesh其實也是可以做到的。只是算法複雜一點。

這裏不能給出完整的代碼，原理可能不是說得太清楚，但願給想實現的人一個思路指引吧。

動畫類裏面，最核心就是擴展Animation類，重寫applyTransformation方法。

7，實現代碼

InhaleAnimationActivity.java

package com.nj1s.lib.test.anim;
import android.os.Bundle;
import android.view.Gravity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import com.nj1s.lib.mesh.InhaleMesh.InhaleDir;
import com.nj1s.lib.test.GABaseActivity;
import com.nj1s.lib.test.R;
import com.nj1s.lib.test.effect.BitmapMesh;
public class InhaleAnimationActivity extends GABaseActivity
{
    private static final boolean DEBUG_MODE = false;
    private BitmapMesh.SampleView mSampleView = null;
                                                              
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
                                                                  
        LinearLayout linearLayout = new LinearLayout(this);
                                                                  
        mSampleView = new BitmapMesh.SampleView(this);
        mSampleView.setIsDebug(DEBUG_MODE);
        mSampleView.setLayoutParams(new LinearLayout.LayoutParams(-1, -1));
        Button btn = new Button(this);
        btn.setText("Run");
        btn.setTextSize(20.0f);
        btn.setLayoutParams(new LinearLayout.LayoutParams(150, -2));
        btn.setOnClickListener(new View.OnClickListener()
        {
            boolean mReverse = false;
                                                                      
            @Override
            public void onClick(View v)
            {
                if (mSampleView.startAnimation(mReverse))
                {
                    mReverse = !mReverse;
                }
            }
        });
                                                                  
        linearLayout.setOrientation(LinearLayout.VERTICAL);
        linearLayout.setGravity(Gravity.CENTER_VERTICAL);
        linearLayout.addView(btn);
        linearLayout.addView(mSampleView);
                                                                  
        setContentView(linearLayout);
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        getMenuInflater().inflate(R.menu.inhale_anim_menu, menu);
        return true;
    }
    @Override
    public boolean onOptionsItemSelected(MenuItem item)
    {
        switch(item.getItemId())
        {
        case R.id.menu_inhale_down:
            mSampleView.setInhaleDir(InhaleDir.DOWN);
            break;
                                                                      
        case R.id.menu_inhale_up:
            mSampleView.setInhaleDir(InhaleDir.UP);
            break;
                                                                      
        case R.id.menu_inhale_left:
            mSampleView.setInhaleDir(InhaleDir.LEFT);
            break;
                                                                      
        case R.id.menu_inhale_right:
            mSampleView.setInhaleDir(InhaleDir.RIGHT);
            break;
        }
                                                                  
        return super.onOptionsItemSelected(item);
    }
}

BitmapMesh.java

package com.nj1s.lib.test.effect;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.Path;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.Interpolator;
import android.view.animation.Transformation;
import com.nj1s.lib.mesh.InhaleMesh;
import com.nj1s.lib.mesh.InhaleMesh.InhaleDir;
import com.nj1s.lib.test.R;
public class BitmapMesh {
                                                      
    public static class SampleView extends View {
                                                          
        private static final int WIDTH = 40;
        private static final int HEIGHT = 40;
        private final Bitmap mBitmap;
        private final Matrix mMatrix = new Matrix();
        private final Matrix mInverse = new Matrix();
                                                          
        private boolean mIsDebug = false;
        private Paint mPaint = new Paint();
        private float[] mInhalePt = new float[] {0, 0};
        private InhaleMesh mInhaleMesh = null;
        public SampleView(Context context) {
            super(context);
            setFocusable(true);
            mBitmap = BitmapFactory.decodeResource(getResources(),
                                                     R.drawable.beach);
                                                              
            mInhaleMesh = new InhaleMesh(WIDTH, HEIGHT);
            mInhaleMesh.setBitmapSize(mBitmap.getWidth(), mBitmap.getHeight());
            mInhaleMesh.setInhaleDir(InhaleDir.DOWN);
        }
                                                          
        public void setIsDebug(boolean isDebug)
        {
            mIsDebug = isDebug;
        }
                                                          
        public void setInhaleDir(InhaleMesh.InhaleDir dir)
        {
            mInhaleMesh.setInhaleDir(dir);
                                                              
            float w = mBitmap.getWidth();
            float h = mBitmap.getHeight();
            float endX = 0;
            float endY = 0;
            float dx = 10;
            float dy = 10;
            mMatrix.reset();
                                                              
            switch (dir)
            {
            case DOWN:
                endX = w / 2;
                endY = getHeight() - 20;
                break;
                                                                  
            case UP:
                dy = getHeight() - h - 20;
                endX = w / 2;
                endY = -dy + 10;
                break;
                                                                  
            case LEFT:
                dx = getWidth() - w - 20;
                endX = -dx + 10;
                endY = h / 2;
                break;
                                                                  
            case RIGHT:
                endX = getWidth() - 20;
                endY = h / 2;
                break;
            }
                                                              
            mMatrix.setTranslate(dx, dy);
            mMatrix.invert(mInverse);
            buildPaths(endX, endY);
            buildMesh(w, h);
            invalidate();
        }
                                                          
        @Override
        protected void onSizeChanged(int w, int h, int oldw, int oldh)
        {
            super.onSizeChanged(w, h, oldw, oldh);
                                                              
            float bmpW = mBitmap.getWidth();
            float bmpH = mBitmap.getHeight();
                                                              
            mMatrix.setTranslate(10, 10);
            //mMatrix.setTranslate(10, 10);
            mMatrix.invert(mInverse);
                                                              
            mPaint.setColor(Color.RED);
            mPaint.setStrokeWidth(2);
            mPaint.setAntiAlias(true);
                                                              
            buildPaths(bmpW / 2, h - 20);
            buildMesh(bmpW, bmpH);
        }
        public boolean startAnimation(boolean reverse)
        {
            Animation anim = this.getAnimation();
            if (null != anim && !anim.hasEnded())
            {
                return false;
            }
                                                              
            PathAnimation animation = new PathAnimation(0, HEIGHT + 1, reverse,
                    new PathAnimation.IAnimationUpdateListener()
            {
                @Override
                public void onAnimUpdate(int index)
                {
                    mInhaleMesh.buildMeshes(index);
                    invalidate();
                }
            });
                                                              
            if (null != animation)
            {
                animation.setDuration(1000);
                this.startAnimation(animation);
            }
                                                              
            return true;
        }
                                                          
        @Override
        protected void onDraw(Canvas canvas)
        {
            Log.i("leehong2", "onDraw  =========== ");
            canvas.drawColor(0xFFCCCCCC);
            canvas.concat(mMatrix);
                                                              
            canvas.drawBitmapMesh(mBitmap,
                    mInhaleMesh.getWidth(),
                    mInhaleMesh.getHeight(),
                    mInhaleMesh.getVertices(),
                    0, null, 0, mPaint);
                                                              
            // ===========================================
            // Draw the target point.
            mPaint.setColor(Color.RED);
            mPaint.setStyle(Style.FILL);
            canvas.drawCircle(mInhalePt[0], mInhalePt[1], 5, mPaint);
                                                              
            if (mIsDebug)
            {
                // ===========================================
                // Draw the mesh vertices.
                canvas.drawPoints(mInhaleMesh.getVertices(), mPaint);
                                                                  
                // ===========================================
                // Draw the paths
                mPaint.setColor(Color.BLUE);
                mPaint.setStyle(Style.STROKE);
                Path[] paths = mInhaleMesh.getPaths();
                for (Path path : paths)
                {
                    canvas.drawPath(path, mPaint);
                }
            }
        }
                                                          
        private void buildMesh(float w, float h)
        {
            mInhaleMesh.buildMeshes(w, h);
        }
                                                          
        private void buildPaths(float endX, float endY)
        {
            mInhalePt[0] = endX;
            mInhalePt[1] = endY;
            mInhaleMesh.buildPaths(endX, endY);
        }
                                                          
        int mLastWarpX = 0;
        int mLastWarpY = 0;
        @Override
        public boolean onTouchEvent(MotionEvent event)
        {
            float[] pt = { event.getX(), event.getY() };
            mInverse.mapPoints(pt);
            if (event.getAction() == MotionEvent.ACTION_UP)
            {
                int x = (int)pt[0];
                int y = (int)pt[1];
                if (mLastWarpX != x || mLastWarpY != y) {
                    mLastWarpX = x;
                    mLastWarpY = y;
                    buildPaths(pt[0], pt[1]);
                    invalidate();
                }
            }
            return true;
        }
    }
                                                      
    private static class PathAnimation extends Animation
    {
        public interface IAnimationUpdateListener
        {
            public void onAnimUpdate(int index);
        }
                                                          
        private int mFromIndex = 0;
        private int mEndIndex = 0;
        private boolean mReverse = false;
        private IAnimationUpdateListener mListener = null;
                                                          
        public PathAnimation(int fromIndex, int endIndex, boolean reverse, IAnimationUpdateListener listener)
        {
            mFromIndex = fromIndex;
            mEndIndex = endIndex;
            mReverse = reverse;
            mListener = listener;
        }
                                                          
        public boolean getTransformation(long currentTime, Transformation outTransformation) {
                                                              
            boolean more = super.getTransformation(currentTime, outTransformation);
            Log.d("leehong2", "getTransformation    more = " + more);
            return more;
        }
                                                          
        @Override
        protected void applyTransformation(float interpolatedTime, Transformation t)
        {
            int curIndex = 0;
            Interpolator interpolator = this.getInterpolator();
            if (null != interpolator)
            {
                float value = interpolator.getInterpolation(interpolatedTime);
                interpolatedTime = value;
            }
                                                              
            if (mReverse)
            {
                interpolatedTime = 1.0f - interpolatedTime;
            }
                                                              
            curIndex = (int)(mFromIndex + (mEndIndex - mFromIndex) * interpolatedTime);
                                                              
            if (null != mListener)
            {
                Log.i("leehong2", "onAnimUpdate  =========== curIndex = " + curIndex);
                mListener.onAnimUpdate(curIndex);
            }
        }
    }
}

最核心的類

InhaleMesh

package com.nj1s.lib.mesh;
import android.graphics.Path;
import android.graphics.PathMeasure;
public class InhaleMesh extends Mesh
{
    public enum InhaleDir
    {
        UP,
        DOWN,
        LEFT,
        RIGHT,
    }
                                              
    private Path mFirstPath  = new Path();
    private Path mSecondPath = new Path();
    private PathMeasure mFirstPathMeasure  = new PathMeasure();
    private PathMeasure mSecondPathMeasure = new PathMeasure();
    private InhaleDir mInhaleDir = InhaleDir.DOWN;
                                              
    public InhaleMesh(int width, int height)
    {
        super(width, height);
    }
                                              
    public void setInhaleDir(InhaleDir inhaleDir)
    {
        mInhaleDir = inhaleDir;
    }
                                              
    public InhaleDir getInhaleDir()
    {
        return mInhaleDir;
    }
    @Override
    public void buildPaths(float endX, float endY)
    {
        if (mBmpWidth <= 0 || mBmpHeight <= 0)
        {
            throw new IllegalArgumentException(
                    "Bitmap size must be > 0, do you call setBitmapSize(int, int) method?");
        }
                                                  
        switch (mInhaleDir)
        {
        case UP:
            buildPathsUp(endX, endY);
            break;
                                                      
        case DOWN:
            buildPathsDown(endX, endY);
            break;
                                                      
        case RIGHT:
            buildPathsRight(endX, endY);
            break;
                                                      
        case LEFT:
            buildPathsLeft(endX, endY);
            break;
        }
    }
    @Override
    public void buildMeshes(int index)
    {
        if (mBmpWidth <= 0 || mBmpHeight <= 0)
        {
            throw new IllegalArgumentException(
                    "Bitmap size must be > 0, do you call setBitmapSize(int, int) method?");
        }
                                                  
        switch (mInhaleDir)
        {
        case UP:
        case DOWN:
            buildMeshByPathOnVertical(index);
            break;
                                                      
        case RIGHT:
        case LEFT:
            buildMeshByPathOnHorizontal(index);
            break;
        }
    }
                                              
    public Path[] getPaths()
    {
        return new Path[] { mFirstPath, mSecondPath };
    }
                                              
    private void buildPathsDown(float endX, float endY)
    {
        mFirstPathMeasure.setPath(mFirstPath, false);
        mSecondPathMeasure.setPath(mSecondPath, false);
                                                  
        float w = mBmpWidth;
        float h = mBmpHeight;
                                                  
        mFirstPath.reset();
        mSecondPath.reset();
        mFirstPath.moveTo(0, 0);
        mSecondPath.moveTo(w, 0);
                                                  
        mFirstPath.lineTo(0, h);
        mSecondPath.lineTo(w, h);
                                                  
        mFirstPath.quadTo(0, (endY + h) / 2, endX, endY);
        mSecondPath.quadTo(w, (endY + h) / 2, endX, endY);
    }
                                              
    private void buildPathsUp(float endX, float endY)
    {
        mFirstPathMeasure.setPath(mFirstPath, false);
        mSecondPathMeasure.setPath(mSecondPath, false);
                                                  
        float w = mBmpWidth;
        float h = mBmpHeight;
                                                  
        mFirstPath.reset();
        mSecondPath.reset();
        mFirstPath.moveTo(0, h);
        mSecondPath.moveTo(w, h);
                                                  
        mFirstPath.lineTo(0, 0);
        mSecondPath.lineTo(w, 0);
                                                  
        mFirstPath.quadTo(0, (endY - h) / 2, endX, endY);
        mSecondPath.quadTo(w, (endY - h) / 2, endX, endY);
    }
                                              
    private void buildPathsRight(float endX, float endY)
    {
        mFirstPathMeasure.setPath(mFirstPath, false);
        mSecondPathMeasure.setPath(mSecondPath, false);
                                                  
        float w = mBmpWidth;
        float h = mBmpHeight;
                                                  
        mFirstPath.reset();
        mSecondPath.reset();
                                                  
        mFirstPath.moveTo(0, 0);
        mSecondPath.moveTo(0, h);
                                                  
        mFirstPath.lineTo(w, 0);
        mSecondPath.lineTo(w, h);
                                                  
        mFirstPath.quadTo((endX + w) / 2, 0, endX, endY);
        mSecondPath.quadTo((endX + w) / 2, h, endX, endY);
    }
                                              
    private void buildPathsLeft(float endX, float endY)
    {
        mFirstPathMeasure.setPath(mFirstPath, false);
        mSecondPathMeasure.setPath(mSecondPath, false);
                                                  
        float w = mBmpWidth;
        float h = mBmpHeight;
                                                  
        mFirstPath.reset();
        mSecondPath.reset();
                                                  
        mFirstPath.moveTo(w, 0);
        mSecondPath.moveTo(w, h);
                                                  
        mFirstPath.lineTo(0, 0);
        mSecondPath.lineTo(0, h);
                                                  
        mFirstPath.quadTo((endX - w) / 2, 0, endX, endY);
        mSecondPath.quadTo((endX - w) / 2, h, endX, endY);
    }
                                              
    private void buildMeshByPathOnVertical(int timeIndex)
    {
        mFirstPathMeasure.setPath(mFirstPath, false);
        mSecondPathMeasure.setPath(mSecondPath, false);
                                                  
        int index = 0;
        float[] pos1 = {0.0f, 0.0f};
        float[] pos2 = {0.0f, 0.0f};
        float firstLen  = mFirstPathMeasure.getLength();
        float secondLen = mSecondPathMeasure.getLength();
                                                  
        float len1 = firstLen / HEIGHT;
        float len2 = secondLen / HEIGHT;
                                                  
        float firstPointDist  = timeIndex * len1;
        float secondPointDist = timeIndex * len2;
        float height = mBmpHeight;
                                                  
        mFirstPathMeasure.getPosTan(firstPointDist, pos1, null);
        mFirstPathMeasure.getPosTan(firstPointDist + height, pos2, null);
        float x1 = pos1[0];
        float x2 = pos2[0];
        float y1 = pos1[1];
        float y2 = pos2[1];
        float FIRST_DIST  = (float)Math.sqrt( (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) );
        float FIRST_H = FIRST_DIST / HEIGHT;
                                                  
        mSecondPathMeasure.getPosTan(secondPointDist, pos1, null);
        mSecondPathMeasure.getPosTan(secondPointDist + height, pos2, null);
        x1 = pos1[0];
        x2 = pos2[0];
        y1 = pos1[1];
        y2 = pos2[1];
                                                  
        float SECOND_DIST = (float)Math.sqrt( (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) );
        float SECOND_H = SECOND_DIST / HEIGHT;
                                                  
        if (mInhaleDir == InhaleDir.DOWN)
        {
            for (int y = 0; y <= HEIGHT; ++y)
            {
                mFirstPathMeasure.getPosTan(y * FIRST_H + firstPointDist, pos1, null);
                mSecondPathMeasure.getPosTan(y * SECOND_H + secondPointDist, pos2, null);
                                                          
                float w = pos2[0] - pos1[0];
                float fx1 = pos1[0];
                float fx2 = pos2[0];
                float fy1 = pos1[1];
                float fy2 = pos2[1];
                float dy = fy2 - fy1;
                float dx = fx2 - fx1;
                                                          
                for (int x = 0; x <= WIDTH; ++x)
                {
                    // y = x * dy / dx
                    float fx = x * w / WIDTH;
                    float fy = fx * dy / dx;
                                                              
                    mVerts[index * 2 + 0] = fx + fx1;
                    mVerts[index * 2 + 1] = fy + fy1;
                                                              
                    index += 1;
                }
            }
        }
        else if (mInhaleDir == InhaleDir.UP)
        {
            for (int y = HEIGHT; y >= 0; --y)
            {
                mFirstPathMeasure.getPosTan(y * FIRST_H + firstPointDist, pos1, null);
                mSecondPathMeasure.getPosTan(y * SECOND_H + secondPointDist, pos2, null);
                                                          
                float w = pos2[0] - pos1[0];
                float fx1 = pos1[0];
                float fx2 = pos2[0];
                float fy1 = pos1[1];
                float fy2 = pos2[1];
                float dy = fy2 - fy1;
                float dx = fx2 - fx1;
                                                          
                for (int x = 0; x <= WIDTH; ++x)
                {
                    // y = x * dy / dx
                    float fx = x * w / WIDTH;
                    float fy = fx * dy / dx;
                                                              
                    mVerts[index * 2 + 0] = fx + fx1;
                    mVerts[index * 2 + 1] = fy + fy1;
                                                              
                    index += 1;
                }
            }
        }
    }
                                              
    private void buildMeshByPathOnHorizontal(int timeIndex)
    {
        mFirstPathMeasure.setPath(mFirstPath, false);
        mSecondPathMeasure.setPath(mSecondPath, false);
                                                  
        int index = 0;
        float[] pos1 = {0.0f, 0.0f};
        float[] pos2 = {0.0f, 0.0f};
        float firstLen  = mFirstPathMeasure.getLength();
        float secondLen = mSecondPathMeasure.getLength();
                                                  
        float len1 = firstLen / WIDTH;
        float len2 = secondLen / WIDTH;
                                                  
        float firstPointDist  = timeIndex * len1;
        float secondPointDist = timeIndex * len2;
        float width = mBmpWidth;
                                                  
        mFirstPathMeasure.getPosTan(firstPointDist, pos1, null);
        mFirstPathMeasure.getPosTan(firstPointDist + width, pos2, null);
        float x1 = pos1[0];
        float x2 = pos2[0];
        float y1 = pos1[1];
        float y2 = pos2[1];
        float FIRST_DIST  = (float)Math.sqrt( (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) );
        float FIRST_X = FIRST_DIST / WIDTH;
                                                  
        mSecondPathMeasure.getPosTan(secondPointDist, pos1, null);
        mSecondPathMeasure.getPosTan(secondPointDist + width, pos2, null);
        x1 = pos1[0];
        x2 = pos2[0];
        y1 = pos1[1];
        y2 = pos2[1];
                                                  
        float SECOND_DIST = (float)Math.sqrt( (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) );
        float SECOND_X = SECOND_DIST / WIDTH;
                                                  
        if (mInhaleDir == InhaleDir.RIGHT)
        {
            for (int x = 0; x <= WIDTH; ++x)
            {
                mFirstPathMeasure.getPosTan(x * FIRST_X + firstPointDist, pos1, null);
                mSecondPathMeasure.getPosTan(x * SECOND_X + secondPointDist, pos2, null);
                                                          
                float h = pos2[1] - pos1[1];
                float fx1 = pos1[0];
                float fx2 = pos2[0];
                float fy1 = pos1[1];
                float fy2 = pos2[1];
                float dy = fy2 - fy1;
                float dx = fx2 - fx1;
                                                          
                for (int y = 0; y <= HEIGHT; ++y)
                {
                    // x = y * dx / dy
                    float fy = y * h / HEIGHT;
                    float fx = fy * dx / dy;
                                                              
                    index = y * (WIDTH + 1) + x;
                                                              
                    mVerts[index * 2 + 0] = fx + fx1;
                    mVerts[index * 2 + 1] = fy + fy1;
                }
            }
        }
        else if (mInhaleDir == InhaleDir.LEFT)
        {
            for (int x = WIDTH; x >= 0; --x)
            //for (int x = 0; x <= WIDTH; ++x)
            {
                mFirstPathMeasure.getPosTan(x * FIRST_X + firstPointDist, pos1, null);
                mSecondPathMeasure.getPosTan(x * SECOND_X + secondPointDist, pos2, null);
                                                          
                float h = pos2[1] - pos1[1];
                float fx1 = pos1[0];
                float fx2 = pos2[0];
                float fy1 = pos1[1];
                float fy2 = pos2[1];
                float dy = fy2 - fy1;
                float dx = fx2 - fx1;
                                                          
                for (int y = 0; y <= HEIGHT; ++y)
                {
                    // x = y * dx / dy
                    float fy = y * h / HEIGHT;
                    float fx = fy * dx / dy;
                                                              
                    index = y * (WIDTH + 1) + WIDTH - x;
                                                              
                    mVerts[index * 2 + 0] = fx + fx1;
                    mVerts[index * 2 + 1] = fy + fy1;
                }
            }
        }
    }
}

Mesh類的實現

package com.nj1s.lib.mesh;
public abstract class Mesh
{
    protected int WIDTH      = 40;
    protected int HEIGHT     = 40;
    protected int mBmpWidth   = -1;
    protected int mBmpHeight  = -1;
    protected final float[] mVerts;
                                      
    public Mesh(int width, int height)
    {
        WIDTH  = width;
        HEIGHT = height;
        mVerts  = new float[(WIDTH + 1) * (HEIGHT + 1) * 2];
    }
                                      
    public float[] getVertices()
    {
        return mVerts;
    }
                                      
    public int getWidth()
    {
        return WIDTH;
    }
                                      
    public int getHeight()
    {
        return HEIGHT;
    }
                                      
    public static void setXY(float[] array, int index, float x, float y)
    {
        array[index*2 + 0] = x;
        array[index*2 + 1] = y;
    }
                                      
    public void setBitmapSize(int w, int h)
    {
        mBmpWidth  = w;
        mBmpHeight = h;
    }
                                      
    public abstract void buildPaths(float endX, float endY);
                                      
    public abstract void buildMeshes(int index);
    public void buildMeshes(float w, float h)
    {
        int index = 0;
                                          
        for (int y = 0; y <= HEIGHT; ++y)
        {
            float fy = y * h / HEIGHT;
            for (int x = 0; x <= WIDTH; ++x)
            {
                float fx = x * w / WIDTH;
                                                  
                setXY(mVerts, index, fx, fy);
                                                  
                index += 1;
            }
        }
    }
}

（本文轉載自：http://blog.csdn.net/leehong2005/article/details/9127095）

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