What is clipping and how can the MMX architecture be used to facilitate clipping operations?

Question

What will be an ideal response?

Answer 1

Clipping is used in graphics to hide some objects behind others. The fundamental operation in clipping is that a
value is constrained to a range. For example, if x is in the range 100 to 199, a value of x = 150 would not change.
A value of x = 34 would become 100 (the lowest legal value), and a value 345 would become 199 (the highest
legal value). You will notice that clipping is rather similar to saturating arithmetic.

We can see how clipping works by taking a simple example with 4?bit arithmetic. Suppose that saturating
arithmetic has the limits 0 and 15 (using unsigned 4?bit arithmetic). Now, suppose that the clipping range is 3 to
10. If we have an unknown value x, we add 5 to it to get x + 5. The value 5 is calculated by maximum saturation
level ? maximum clipping level (in this case 15 ? 10 = 5). Having done that, we subtract 5 from this value. If we
are within range, we will end up where we started from (x + 5) ? 5 = x. Now suppose x was 12, which is outside
its upper limit. Adding 5 gives 12 + 5 = 17 and that is reduced to 15 because of the saturating arithmetic. When
we subtract 5 from the clamped value of 15 the result is 10. We’ve clipped it.