Odd fog formulas

[JayFoxRox]

I noticed that some of the fog formulas might be weird. I'm not sure how I came up with them anymore either. See espes/xqemu#35

Note how the sheet does:

• fogParam[1] = 1 / (start - end) but the code below uses 1 / (end - start).
• fogParam[0] = 1 - end * fogParam[1] but the code below uses 1 + end * fogParam[1].

This is currently just a theory, it's possible I did miss another step somewhere.

Documentation of formula (GL) and inputs (D3D):

/* f = (end - d) / (end - start)
 *    fogParam[1] = 1 / (end - start)
 *    fogParam[0] = 1 + end * fogParam[1] = 1 + end / (end - start);
 */

Current implementation:

float fogFactor = fogParam[0] + fogDistance * fogParam[1] - 1.0;
float fogFactor = 1 + end / (end - start) + fogDistance / (end - start) - 1.0;
float fogFactor = end / (end - start) + fogDistance / (end - start);
float fogFactor = (end + fogDistance) / (end - start);

Proposed fix:

float fogFactor = fogParam[0] - fogDistance * fogParam[1] - 1.0;
float fogFactor = 1 + end / (end - start) - fogDistance / (end - start) - 1.0;
float fogFactor = end / (end - start) - fogDistance / (end - start);
float fogFactor = (end - fogDistance) / (end - start);

Alternative fix (inverted fog factor): Nevermind, this is broken:

float fogFactor = fogDistance * fogParam[1] - fogParam[0];
float fogFactor = fogDistance / (end - start) - end / (end - start) - 1.0;
float fogFactor = (fogDistance - end) / (end - start) - 1.0 = -(end - fogDistance) / (end - start) - 1.0

[JayFoxRox]

The original formulas seem to be fine, but the comments are wrong?

fogParam[1] = 1 / (end - start) should be fogParam[1] = -1 / (end - start) or fogParam[1] = 1 / (start - end)