Determining distance before a sphere goes subpixel

Hi all,

The subject says it all. I'd like to know at what distance a sphere is roughly subpixel.

- First I calculate the screen size in world space:

screenSize = nearPlane * tangent( fieldOfView / 2 );

- Then I determine the size of a pixel in world space:

pixelWorldSize = screenWorld Size / ( screenResolution / 2.0f );

- Then I use the law of similar triangles to solve for distance:

worldDistance = radius * near / pixelSize

It seems to work well in my testing. I'm eyeballing it, plus multiplying transforming a sphere at this distance into screenSpace to check the extents are within a pixel.

Does this all sound reasonable? Also, any tips for testing?

Thanks,
unfadable