Does anyone know what the ddx and ddy values do in the AABB ray intersect algorithm? Taken from the following site http://www.blitzbasic.com/codearcs/codearcs.php?code=1029 (show below).
Local txmin#,txmax#,tymin#,tymax#
// rox, rdx are the ray origin on the x axis, and ray delta on the x axis ... y-axis is roy and rdy
Local ddx# =1.0/(rox-rdx)
Local ddy# =1.0/(roy-rdy)
If ddx >= 0
txmin = (bminx - rox) * ddx
txmax = (bmaxx - rox) * ddx
Else
txmin = (bmaxx - rox) * ddx
txmax = (bminx - rox) * ddx
EndIf
If ddy >= 0
tymin = (bminy - roy) * ddy
tymax = (bmaxy - roy) * ddy
Else
tymin = (bmaxy - roy) * ddy
tymax = (bminy - roy) * ddy
EndIf
If ( (txmin > tymax) Or (tymin > txmax) ) Return 0
If (tymin > txmin) txmin = tymin
If (tymax < txmax) txmax = tymax
Local tzmin#,tzmax#
Local ddz# =1.0/(roz-rdz)
If ddz >= 0
tzmin = (bminz - roz) * ddz
tzmax = (bmaxz - roz) * ddz
Else
tzmin = (bmaxz - roz) * ddz
tzmax = (bminz - roz) * ddz
EndIf
If (txmin > tzmax) Or (tzmin > txmax) Return 0
Return 1