OBD:PLEA

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Revision as of 09:30, 12 September 2007 by Ssg (talk | contribs) (design)
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ONI BINARY DATA
OTLF << Other file types >> PNTA
PLEA : Plane Equation Array
switch to XML:PLEA page
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OBD.png


Plea a.gif


Offset Type Raw Hex Value Description
0x00 res_id 01 41 02 00 577 00577-.PLEA
0x04 lev_id 01 00 00 06 3 level 3
0x08 char[20] AD DE dead unused
0x1C int32 03 00 00 00 13554 array size
First element (black outline)
0x00 float 00 00 00 00 0.000000 1st coefficient of the plane equation (x-part of normal vector)
0x04 float 00 00 00 00 0.000000 2nd coefficient of the plane equation (y-part of normal vector)
0x08 float 00 00 80 3F 1.000000 3rd coefficient of the plane equation (z-part of normal vector)
0x0C float 00 00 19 44 612.000000 4th coefficient of the plane equation


Plane equation
The canonical equation for a plane in 3D is :
a * x + b * y + c * z + d = 0
where (a, b, c, d) are 4 real numbers. The plane is the set of points (x, y, z) verifying that equation.
It is likely that the four floats in one of a PLEA's packages are exactly the (a, b, c, d) of the above definition.
In that case, the first package of the above example defines the plane (0 * x + 0 * y + 1 * z + 612 = 0), i.e., the vertical plane z = -612.
It is possible, however, that the definition used is different, e.g. : a * x + b * y + c * z = d .
In that case, the first package of the above example defines the plane (0 * x + 0 * y + 1 * z = 612), i.e., the vertical plane z = 612.
Front/back
The 4 numbers (a, b, c, d) can also serve to define whether a 3D point (x, y, z) is on the "front" side of the plane or in the "back".
"points are in front of the plane if a * x + b * y + c * z >= d" (from commented Myth source)
That would mean the plane equation is a * x + b * y + c * z = d , not a * x + b * y + c * z + d = 0 .
It's rather easy to check (just flip the "normal" of the plane equation for a known axis-aligned quad).
The oriented "plane inequation" can be used for: culling; collision.
ONI BINARY DATA
OTLF << Other file types >> PNTA
PLEA : Plane Equation Array
Level file


ONI BINARY DATA
OTLF << Other file types >> PNTA
PLEA : Plane Equation Array
switch to XML:PLEA page
Overview @ Oni Stuff
OBD.png