Archive for category Garbage Collector

Number Display

In my previous post, I mentioned a Number Display that I had created in order to display numbers to the screen without creating any garbage. I thought some people might find it useful, so here it is. It’s relatively simple. You initialize it with a GraphicsDevice, SpriteFont, and some magnitude to define the general size. The Number Display will then create a number palette to be used in displaying the numbers. To draw a number, use the Draw(…) function passing in the number you want to display. The Number Display will finally use a Spritebatch to draw all of the different digits from the palette. Since no strings are used, no garbage is created.

public class NumberDisplay
{
    GraphicsDevice drawDevice;
    SpriteBatch drawBatch;
    Texture2D numberTex;
    Rectangle[] aryNumberRects = new Rectangle[10];

    public NumberDisplay(GraphicsDevice newDevice, SpriteFont newFont, int digitMagnitude)
    {
        drawDevice = newDevice;
        drawBatch = new SpriteBatch(drawDevice);

        int rectSize = 2 * digitMagnitude;
        RenderTarget2D newRender = new RenderTarget2D(drawDevice, 10 * rectSize, rectSize, false,
            SurfaceFormat.Color, DepthFormat.None, 0, RenderTargetUsage.PreserveContents);

        // Create draw rects and texture map
        drawDevice.SetRenderTarget(newRender);
        drawDevice.Clear(Color.Transparent);
        drawBatch.Begin();

        Vector2 digitDim;
        for (int i = 0; i < aryNumberRects.Length; i++)
        {
            digitDim = newFont.MeasureString(i.ToString());
            aryNumberRects[i] = new Rectangle(i * rectSize, 0, rectSize, rectSize);
            drawBatch.DrawString(newFont, i.ToString(), new Vector2(
                aryNumberRects[i].Center.X, aryNumberRects[i].Center.Y), Color.White,
                0.0f, Vector2.Zero, rectSize / Math.Max(digitDim.X, digitDim.Y), SpriteEffects.None, 0.0f);
        }

        drawBatch.End();
        drawDevice.SetRenderTarget(null);
        numberTex = newRender;
    }

    // ***** ACCESSORS *****

    public Texture2D NumberPalette { get { return numberTex; } }

    // ***** USER METHODS *****

    public void Draw(int drawNum, Vector2 drawPos)
    {
        int drawDigit = drawNum;
        drawBatch.Begin();
        do
        {
            drawDigit = drawNum % 10;
            drawBatch.Draw(numberTex, drawPos, aryNumberRects[drawDigit], Color.White);
            drawPos.X -= aryNumberRects[drawDigit].Width;
            drawNum = drawNum / 10;
        } while (drawNum > 0);
        drawBatch.End();
    }
}
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More on the Garbage Collector

Pooled Objects

I had been meaning to come up with some sort of number display so I can write numbers (like the amount of Garbage) to the screen without worrying about it creating garbage. Well, I finally got around to it, and low and behold, my GC came to a complete halt. At first, I wasn’t so sure–perhaps my new number display was a bit off–so I threw in a couple lines that would specifically create garbage. Sure enough the GC kicked right back up again.

As you can imagine, I’m very happy. Now I can know what, exactly, is causing garbage the second I add it in. And already I’ve realized that I was wrong in thinking every class object that is added to a list creates garbage; it doesn’t! When I added those lines to test my display, I apparently had made an error. I added some class objects to a list that were from my already created pool of objects. The problem was that I still wasn’t seeing any garbage. I got a little worried because I figured that that meant there was a bug in my number display, but after a few minutes, I discovered the error.

Rather than adding objects from my pool, I added some newly creates ones–empty objects created in-line with the list. I ran the program and there it was; the GC was creating garbage again.

All this time, I always thought that that adding any class reference to a List would create garbage, but that’s not the case. As long as you add a reference form an object that will never be destroyed–say, one from an object pool–then no garbage will be created.

 

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