Android bitmap placing

Question

I've recently added an explosion in my game, for when enemies get killed, and it works fine and all, but the explosion wont "spawn" on the enemies x and y. The problem is that I'm not drawing the bitmap from the center, but from its 0,0 position, so the explosion spawns at my enemies 0,0. It's not like the explosion spawns at random places, it spawns around the enemies bitmap, but just not on the center, and it is really annoying to look at.

But if I try to change it so I add them at the center, It creates a really weird effect when rotating them that is hard to explain.

I cant use this: canvas.drawBitmap(bitmap, x - bitmap.getWidth/2, y - bitmap.getHeight/2, null);, or I'm just doing it wrong and missing something.

How I draw my enemies:

    public void draw(Canvas canvas) {
    canvas.save();
    canvas.rotate((float) rotater, x + (width / 2), y + (height/2));
    int srcX = currentFrame * width;
    int srcY = 0 * height;
    Rect src = new Rect(srcX, srcY, srcX + width, srcY + height);
    Rect dst = new Rect(x, y, x + width, y + height);
    canvas.drawBitmap(bitmap, src, dst, null);
    canvas.restore();
}

How I add my explosions:

    if (enemies.get(i).getHP() <= 0) {  //enemy death
        addExplosion(enemies.get(i).getX(), enemies.get(i).getY());

If you need any more info to be able to help, let me know. Thank you!

Answer 1

Try something like this (this is pseudocode, I don't know your objects actual fields)

1 - determine the enemy's center.

centerX = enemy.getX() + (enemy.getWidth() /2 );
centerY = enemy.getY() + (enemy.getHeight() / 2);

2 - assume the center of the explosion is the same center of the enemy and determine that explosion top-left from its size

explosion.setX(centerX - (explosion.getWidth() / 2);
explosion.setY(centerY - (explosion.getHeight() / 2);

Answer 2

When you add an explosion, your enemy object should return its center like this: addExplosion(enemies.get(i).getCenterX(), enemies.get(i).getCenterY());

The drawing of an explosion should happen after canvas.restore(); so that is not affected by the enemie's rotation. Every object drawn on Canvas can have its own canvas.save()/cavas.transform/canvas.restore() especially when the rotational pivotal point is not the same for all objects.

Do not create new objects in onDraw, such as new Rect. You can use the same ones with src.set(0,0,0,0);

For each group of objects create a draw method, and in onDraw just call them one by one and pass the canvas. i.e. drawEnemyShips(canvas); drawExplostions(canvas);