OBD:PLEA

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

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	'a' coefficient of the plane equation (x component of plane's normal)
0x04	float	00 00 00 00	0.000000	'b' coefficient of the plane equation (y component of plane's normal)
0x08	float	00 00 80 3F	1.000000	'c' coefficient of the plane equation (z component of plane's normal)
0x0C	float	00 00 19 44	612.000000	'd' coefficient of the plane equation

Plane equation

The canonical equation for a plane in 3D is

a * x + b * y + c * z + d = 0,

with (a, b, c, d) being 4 real numbers and (a, b, c) forming a nonzero vector (the plane's "normal").

• The set of points (x, y, z) verifying a * x + b * y + c * z + d = 0 are said to be in the plane or at the plane.
• The set of points (x, y, z) verifying a * x + b * y + c * z + d > 0 are said to be in front of the plane.
• The set of points (x, y, z) verifying a * x + b * y + c * z + d < 0 are said to be behind the plane.

N.B. If a=b=c=0, then the equation is degenerate and applies either to the whole space (if d=0) or to no points at all (if d is non-zero).

As a further convention, if (a,b,c) is normalized at unit length (i.e., a*a + b*b + c*c = 1) then d is the distance from the plane to the world's origin, along the normal vector.

The four floats in each element of a PLEA are exactly the (a, b, c, d) of the above definition.

In the above example, the first element defines the plane (0 * x + 0 * y + 1 * z + 612 = 0), i.e., the vertical plane z = -612.

What planes are for and how they are referenced

Planes are used for environment culling, collision detection and BSP.

The plane equations stored in PLEA are referenced from such data as ABNA, AKBP, AKBA and AGQC by means of a 32-bit array index.

However, the high bit of those 32-bit references is not part of the array index, instead it indicates whether the facing of the plane should be flipped.

• If the high bit is not set, then the 4 values (a, b, c, d) are used as described above.
  (If referencing the above example without a high bit, then any points with z > - 612 will be in front of the plane, whereas points with z < -612 will be behind the plane.)
• If the high bit is set, then the plane equation coefficients become (-a, -b, -c, -d).
  (If referencing the above example with a high bit, then any point with z > - 612 will be behind the plane, whereas points with z < -612 will be in front of the plane.)

This means that the actual array index is a 31-bit value (i.e., there can only be up to 32768 distinct planes in a level), but the same array element can be used for two different facing directions.

ONI BINARY DATA
OTLF << Other file types >> PNTA
PLEA : Plane Equation Array
Level file