Android使用SurfaceView绘制动态图像
实例 SurfaceViewDrawDemo 绘制的是一幅静态图像,而使用 SurfaceView 可以绘制动态图像。
绘制动态图像的过程应该在一个单独的线程中完成,而不应该在主线程中进行。实例 SurfaceViewDynDrawDemo 演示了使用 SurfaceView 组件绘制动态图像的过程。
该实例修改自 Android SDK 提供的实例,绘制的是类似于 Windows 中的变幻线屏保的效果,运行效果如图 1 所示。
图 1 实例 SurfaceViewDynDrawDemo 的运行效果
实例 SurfaceViewDynDrawDemo 的布局文件 main.xml 内容如下:
绘制动态图像的过程应该在一个单独的线程中完成,而不应该在主线程中进行。实例 SurfaceViewDynDrawDemo 演示了使用 SurfaceView 组件绘制动态图像的过程。
该实例修改自 Android SDK 提供的实例,绘制的是类似于 Windows 中的变幻线屏保的效果,运行效果如图 1 所示。
图 1 实例 SurfaceViewDynDrawDemo 的运行效果
实例 SurfaceViewDynDrawDemo 的布局文件 main.xml 内容如下:
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical"> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" /> <SurfaceView android:id="@+id/surfaceViewl" android:layout_width="fill_parent" android:layout_height="fill_parent" /> </LinearLayout>实例 SurfaceViewDynDrawDemo 的主 Activity 为 SurfaceViewDynDrawDemoActivity,其代码如下:
import android.app.Activity; import android.graphics.Canvas; import android.graphics.Paint; import android.os.Bundle; import android.util.Log; import android.view.SurfaceHolder; import android.view.SurfaceView; public class SurfaceViewDynDrawDemoActivity extends Activity { private SurfaceView mySurfaceView; private DrawingThread mDrawingThread; SurfaceHolder surfaceHolder; /** * Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mySurfaceView = (SurfaceView) findViewById(R.id.surfaceViewl); surfaceHolder = mySurfaceView.getHolder(); surfaceHolder.addCallback(new SurfaceHolder.Callback() { @Override public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) { // TODO Auto-generated method stub } @Override public void surfaceCreated(SurfaceHolder holder) { // TODO Auto-generated method stub mDrawingThread = new DrawingThread(); mDrawingThread.mSurface = surfaceHolder; mDrawingThread.start(); } @Override public void surfaceDestroyed(SurfaceHolder holder) { // TODO Auto-generated method stub mDrawingThread.mQuit = true; } }); } static final class MovingPoint { float x, y, dx, dy; void init(int width, int height, float minStep) { x = (float) ((width - 1) * Math.random()); y = (float) ((height - 1) * Math.random()); dx = (float) (Math.random() * minStep * 2) + 1; dy = (float) (Math.random() * minStep * 2) + 1; } float adjDelta(float cur, float minStep, float maxStep) { cur += (Math.random() * minStep) - (minStep / 2); if (cur < 0 && cur > -minStep) cur = -minStep; if (cur >= 0 && cur < minStep) cur = minStep; if (cur > maxStep) cur = maxStep; if (cur < -maxStep) cur = -maxStep; return cur; } void step(int width, int height, float minStep, float maxStep) { x += dx; if (x <= 0 || x >= (width - 1)) { if (x <= 0) x = 0; else if (x >= (width - 1)) x = width - 1; dx = adjDelta(-dx, minStep, maxStep); } y += dy; if (y <= 0 || y >= (height - 1)) { if (y <= 0) y = 0; else if (y >= (height - 1)) y = height - 1; dy = adjDelta(-dy, minStep, maxStep); } } } class DrawingThread extends Thread { // These are protected by the Thread's lock SurfaceHolder mSurface; boolean mRunning; boolean mActive; boolean mQuit; // Internal state int mLineWidth; float mMinStep; float mMaxStep; boolean mInitialized = false; final MovingPoint mPoint1 = new MovingPoint(); final MovingPoint mPoint2 = new MovingPoint(); static final int NUM_OLD = 100; int mNum0ld = 0; final float[] m0ld = new float[NUM_OLD * 4]; final int[] m01dColor = new int[NUM_OLD]; int mBrightLine = 0; // X is red, Y is blue final MovingPoint mColor = new MovingPoint(); final Paint mBackground = new Paint(); final Paint mForeground = new Paint(); int makeGreen(int index) { int dist = Math.abs(mBrightLine - index); if (dist > 10) return 0; return (255 - (dist * (255 / 10))) << 8; } @Override public void run() { mLineWidth = (int) (getResources().getDisplayMetrics().density * 1.5); if (mLineWidth < 1) mLineWidth = 1; mMinStep = mLineWidth * 2; mMaxStep = mMinStep * 3; mBackground.setColor(0xff000000); mForeground.setColor(0xff00ffff); mForeground.setAntiAlias(false); mForeground.setStrokeWidth(mLineWidth); while (true) { if (mQuit) { return; } // Lock the canvas for drawing Canvas canvas = mSurface.lockCanvas(); if (canvas == null) { Log.i("WindowSurface", "Failure locking canvas"); continue; } // Update graphics if (!mInitialized) { mInitialized = true; mPoint1.init(canvas.getWidth(), canvas.getHeight(), mMinStep); mPoint2.init(canvas.getWidth(), canvas.getHeight(), mMinStep); mColor.init(127, 127, 1); } else { mPoint1.step(canvas.getWidth(), canvas.getHeight(), mMinStep, mMaxStep); mPoint2.step(canvas.getWidth(), canvas.getHeight(), mMinStep, mMaxStep); mColor.step(127, 127, 1, 3); } mBrightLine += 2; if (mBrightLine > (NUM_OLD * 2)) { mBrightLine = -2; } // Clear background canvas.drawColor(mBackground.getColor()); // Draw old lines for (int i = mNum0ld - 1; i >= 0; i--) { mForeground.setColor(m01dColor[i] | makeGreen(i)); mForeground.setAlpha(((NUM_OLD - i) * 255) / NUM_OLD); int p = i * 4; canvas.drawLine(m0ld[p], m0ld[p + 1], m0ld[p + 2], m0ld[p + 3], mForeground); } // Draw new line int red = (int) mColor.x + 128; if (red > 255) red = 255; int blue = (int) mColor.y + 128; if (blue > 255) blue = 255; int color = 0xff000000 | (red << 16) | blue; mForeground.setColor(color | makeGreen(-2)); canvas.drawLine(mPoint1.x, mPoint1.y, mPoint2.x, mPoint2.y, mForeground); // Add in the new line if (mNum0ld > 1) { System.arraycopy(m0ld, 0, m0ld, 4, (mNum0ld - 1) * 4); System.arraycopy(m01dColor, 0, m01dColor, 1, mNum0ld - 1); } if (mNum0ld < NUM_OLD) mNum0ld++; m0ld[0] = mPoint1.x; m0ld[1] = mPoint1.y; m0ld[2] = mPoint2.x; m0ld[3] = mPoint2.y; m01dColor[0] = color; // All done mSurface.unlockCanvasAndPost(canvas); } } } }需要注意的是,就像前面所提到的,绘制动态图像的过程必须在一个单独的线程中完成,而不能在主线程中进行。在该实例中,绘图过程是在 DrawingThread 中完成的。
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