Question

I’m playing with MonoGame right now, and I was investigating the SpriteBatch.Draw() method.

Inside of the method, which can be called tens of thousands of times per second, I see the following:

public void Draw (Texture2D texture,
        Rectangle destinationRectangle,
        Rectangle? sourceRectangle,
        Color color,
        float rotation,
        Vector2 origin,
        SpriteEffects effect,
        float depth)
    {
        CheckValid(texture);

        DrawInternal(texture,
              new Vector4(destinationRectangle.X, //<-------------- Oh Noes! :O
                          destinationRectangle.Y,
                          destinationRectangle.Width,
                          destinationRectangle.Height),
              sourceRectangle,
              color,
              rotation,
              new Vector2(origin.X * ((float)destinationRectangle.Width (float)texture.Width), <-- Oh Noes!
                          origin.Y * ((float)destinationRectangle.Height / (float)texture.Height)),
              effect,
              depth);
    }

It would seem that thousands of new vectors are being allocated every 60th of a second or so.

MonoGame is a platform which is meant for (among other things) mobile development. I did some mobile development which ran on Dalvik, and allocating in this manner was never a good idea. On slow mobile processors the build up of objects in need of collection would eventually cause GC to run and cause a noticeable dip in performance (up to 200 milliseconds on some devices). Which leads me to my question:

Is there something about the way the CLR/Mono GC runs, or some other factor, that would prevent this performance hit from occurring, or is MonoGame doing something it shouldn’t in one of its most called functions?

Answer 1

The Vector4 type is not a class, it’s a structure. Creating a new instance of it doesn’t create an object on the heap, it creates a structure value. In this case the value is pushed onto the stack for the method call, so it’s basically the same work as pushing the members as separate parameters.