如何使用游戏循环每五秒在屏幕上出现和消失一个对象

Posted 2023-03-10

【中文标题】如何使用游戏循环每五秒在屏幕上出现和消失一个对象

【英文标题】：How to appear and disappear an object on screen using game loop for every five second

【发布时间】：2012-09-05 12:53:03

【问题描述】：

我正在尝试学习 android 中的游戏开发。首先，我尝试每五秒钟使用游戏循环在屏幕上出现和消失一个对象。但我没有成功。我读过不同的教程和论坛。我在教程中应用了所有东西，但对象仍在连续绘制。它并没有消失。我没有得到我所缺少的东西？请指导我。

完整代码在这里：

MainGameActivity.java

package com.example.showandhideobject;

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.view.WindowManager;

public class MainGameActivity extends Activity 

    @Override
    public void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(new MainGamePanel(this));
      

MainGamePanel .java

package com.example.showandhideobject;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class MainGamePanel extends SurfaceView implements
        SurfaceHolder.Callback 

    private MainGameThread thread;
    private ImageObject image;

    // private long gameStartTime;

    public MainGamePanel(Context context) 
        super(context);
        // adding the callback (this) to the surface holder to intercept events
        getHolder().addCallback(this);
        // create the game loop thread
        thread = new MainGameThread(getHolder(), this);

        Bitmap imageBitMap = BitmapFactory.decodeResource(getResources(),
                R.drawable.rose);
        image = new ImageObject(imageBitMap, 100, 150);
        image.setAppeared(false);
        image.setDisappearTime(System.currentTimeMillis());

        // make the GamePanel focusable so it can handle events
        setFocusable(true);
    

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width,
            int height) 
    

    @Override
    public void surfaceCreated(SurfaceHolder holder) 
        // at this point the surface is created and
        // we can safely start the game loop

        thread.setRunning(true);
        thread.start();

    

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) 
    

    public void update() 

        Log.i("Image Status:::::::::::::    ",
                Boolean.valueOf(image.isAppeared()).toString());

        if (!image.isAppeared()
                && System.currentTimeMillis() - image.getDisappearTime() >= 5000) 

            Log.i("Image Object:::::::  ", "Showing");
            image.setAppeared(true);
            image.setAppearTime(System.currentTimeMillis());

        
        if (image.isAppeared()
                && (System.currentTimeMillis() - image.getAppearTime() >= 5000)) 

            Log.i("Image Object:::::::  ", "Not Showing");
            image.setAppeared(false);
            image.setDisappearTime(System.currentTimeMillis());
        
    

    public void render(Canvas canvas) 

        if (image.isAppeared()) 
            image.draw(canvas);
        
    

MainGameThread.java

package com.example.showandhideobject;

import android.graphics.Canvas;
import android.util.Log;
import android.view.SurfaceHolder;

public class MainGameThread extends Thread 

    // Surface holder that can access the physical surface
    private SurfaceHolder surfaceHolder;

    // The actual view that handles inputs
    // and draws to the surface
    private MainGamePanel gamePanel;

    // flag to hold game state
    private boolean running;

    public boolean isRunning() 
        return running;
    

    public void setRunning(boolean running) 
        this.running = running;
    

    public MainGameThread(SurfaceHolder surfaceHolder, MainGamePanel gamePanel) 
        super();
        this.surfaceHolder = surfaceHolder;
        this.gamePanel = gamePanel;
    

    @Override
    public void run() 
        Canvas canvas;

        while (isRunning()) 
            canvas = null;
            // try locking the canvas for exclusive pixel editing
            // in the surface
            try 
                canvas = this.surfaceHolder.lockCanvas();
                synchronized (surfaceHolder) 
                    Log.i("With in :::::::::", "Game Loop");
                    // update game state
                    gamePanel.update();
                    // render state to the screen and draw the canvas on the
                    // panel

                    gamePanel.render(canvas);
                    // gamePanel.onDraw(canvas);
                
             finally 
                // in case of an exception the surface is not left in an
                // inconsistent state
                if (canvas != null) 
                    surfaceHolder.unlockCanvasAndPost(canvas);
                
             // end finally
        
    

ImageObject.java

package com.example.showandhideobject;

import android.graphics.Bitmap;
import android.graphics.Canvas;

public class ImageObject 

    private Bitmap bitmap; // the actual bitmap
    private int x; // the X coordinate
    private int y; // the Y coordinate
    private boolean isAppeared;
    private long appearTime;
    private long disappearTime;

    // Constructor for this class
    public ImageObject(Bitmap bitmap, int x, int y) 
        this.bitmap = bitmap;
        this.x = x;
        this.y = y;
    

    public Bitmap getBitmap() 
        return bitmap;
    

    public void setBitmap(Bitmap bitmap) 
        this.bitmap = bitmap;
    

    public int getX() 
        return x;
    

    public void setX(int x) 
        this.x = x;
    

    public int getY() 
        return y;
    

    public void setY(int y) 
        this.y = y;
    

    public boolean isAppeared() 
        return isAppeared;
    

    public void setAppeared(boolean isAppeared) 
        this.isAppeared = isAppeared;
    

    public long getAppearTime() 
        return appearTime;
    

    public void setAppearTime(long appearTime) 
        this.appearTime = appearTime;
    

    public long getDisappearTime() 
        return disappearTime;
    

    public void setDisappearTime(long disappearTime) 
        this.disappearTime = disappearTime;
    

    /* Method to draw images on Canvas */
    public void draw(Canvas canvas) 
        canvas.drawBitmap(bitmap, x - (bitmap.getWidth() / 2),
                y - (bitmap.getHeight() / 2), null);
    

【问题讨论】：

乍一看，它似乎过度设计了。

您有一些日志消息：Log.i("Image ... 它们显示了什么？

【参考方案1】：

在这部分

if (image.isAppeared()) 
    image.draw(canvas);

你永远不会清理你的画布。你所做的实际上是在同一个地方一遍又一遍地绘制你的图像。

您可能需要在 cas isAppeared() is false 中重绘背景

编辑

您也可以在绘制图像之前使用 canvas.save()，当您不再需要该图像时使用 canvas.restore()。

【讨论】：

我刚刚使用了 canvas.drawColor(Color.CYAN);在 if 条件之外。 if (image.isAppeared()) image.draw(canvas); 谢谢 njzk2 :)

【参考方案2】：

不要尝试过早优化，游戏渲染通常效率低下，因为几乎所有屏幕的大部分都预计会发生变化。

循环应该是：

始终在画布上绘制背景 始终将所有游戏对象绘制到画布上，让它们决定它们是否可见，这将简化 MainGamePanel 类 最后总是显示画布（通过复制到图像）

扩展第 2 点：

/* Method to draw images on Canvas */  
public void draw(Canvas canvas)  
    if(!isAppeared) return; //let the object decide when it should be drawn
    canvas.drawBitmap(bitmap, x - (bitmap.getWidth() / 2),  
            y - (bitmap.getHeight() / 2), null);  
  

【参考方案3】：

将MainGamePanel.java中的方法render改为

if (image.isAppeared() && canvas != null) 
        image.draw(canvas);