Question

Hi in my application I have an explosion animation that comes up extremely often. when creating an explosion I load 3 images from resources then once the explosion animation is over I recycle those 3 images. I am constantly doing this and have noticed framerate drops. Is their a better way of doing this like static bitmaps or something?

Answer 1

I once made an application, a simple canvas on which bombs exploded.
I used a tiled bitmap composed of each step of the explosion and drew only a part of it, which changes often in order to create the animation effect.
It updates steps automatically following currentTimestamp

So this is the explosion class:

public class ExplosionAnimated {

private static final String TAG = ExplosionAnimated.class.getSimpleName();

private Bitmap mBitmap;
private Rect mSourceRect;
private int mFrameCountX;
private int mFrameCountY;
private int mCurrentFrame;
private long mFrameTicker;
private int mFramePeriod;

private int mSpriteWidth;
private int mSpriteHeight;

private int mX;
private int mY;

private boolean mFinished = false;

public ExplosionAnimated(Bitmap pBitmap, int pX, int pY, 
        int pFrameCountX, int pFrameCountY, int pFps) {

    this.mBitmap = pBitmap;
    this.mX = pX;
    this.mY = pY;
    this.mCurrentFrame = 0;
    this.mFrameCountX = pFrameCountX;
    this.mFrameCountY = pFrameCountY;
    this.mSpriteWidth = pBitmap.getWidth() / pFrameCountX;
    this.mSpriteHeight = pBitmap.getHeight() / pFrameCountY;
    this.mSourceRect = new Rect(0, 0, this.mSpriteWidth, this.mSpriteHeight);
    this.mFramePeriod = 1000 / pFps;
    this.mFrameTicker = 0l;
}

public void update(long gameTime) {

    if (gameTime > this.mFrameTicker + this.mFramePeriod) {
        this.mFrameTicker = gameTime;

        this.mCurrentFrame++;
        if (this.mCurrentFrame >= this.mFramePeriod) {
            this.mCurrentFrame = 0;
            this.mFinished = true;
        }
    }

    if (!this.mFinished) {

        this.mSourceRect.left = this.mCurrentFrame * this.mSpriteWidth;
        this.mSourceRect.right = this.mSourceRect.left + this.mSpriteWidth;
    }
}

public void draw(Canvas canvas) {

    Rect destRect = new Rect(this.mX, this.mY, 
            this.mX + this.mSpriteWidth, 
            this.mY + this.mSpriteHeight);
    canvas.drawBitmap(this.mBitmap, this.mSourceRect, destRect, null);
}

public boolean isFinished() {
    return this.mFinished;
}
}

These are methods from an object (Bomb.java for exemple) that starts explosion and draw it:

public void explode(Context pContext, Canvas pCanvas) {

    this.mState = State.EXPLODING;
    this.mExplosion = new ExplosionAnimated(this.mExplosionBitmap, 
            (int) this.mX, (int) this.mY, 7, 3, 7);
}

public void doDraw(Canvas pCanvas) {

    if (this.mState == State.EXPLODING) {

        if (this.mExplosion.isFinished()) {
            this.mState = State.EXPLODED;
        } else {
            this.mExplosion.update(System.currentTimeMillis());
            this.mExplosion.draw(pCanvas);
        }
    } else {
        pCanvas.drawBitmap(this.mBombBitmap, this.mX, this.mY, null);
    } 
}

I used a Thread and a SurfaceView to continually draw the bomb (or the explosion), giving just the currentTimestamp to update the explosion.

I hope it helps, and if you need I can show and explain more code