69 lines
1.8 KiB
C
69 lines
1.8 KiB
C
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/******************************Module*Header*******************************\
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* Module Name: math.c
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*
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* Useful math routines.
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*
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* Created: 14-Mar-1995 22:35:54
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* Author: Gilman Wong [gilmanw]
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*
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* Copyright (c) 1995 Microsoft Corporation
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*
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\**************************************************************************/
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#include <windows.h>
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#include <math.h>
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#include <gl/gl.h>
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#include "global.h"
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/******************************Public*Routine******************************\
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* calcNorm
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*
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* Compute the normal vector for the given three vertices. Assume CCW
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* ordering.
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*
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* History:
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* 14-Mar-1995 -by- Gilman Wong [gilmanw]
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* Taken from Otto's screen saver code.
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\**************************************************************************/
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void calcNorm(GLfloat *norm, GLfloat *p1, GLfloat *p2, GLfloat *p3)
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{
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GLfloat crossX, crossY, crossZ;
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GLfloat abX, abY, abZ;
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GLfloat acX, acY, acZ;
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GLfloat sqrLength;
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GLfloat invLength;
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if (!norm || !p1 || !p2 || !p3)
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{
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LBprintf("calcNorm: bad array (0x%lx, 0x%lx, 0x%lx, 0x%lx)",
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norm, p1, p2, p3);
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return;
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}
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abX = p2[0] - p1[0]; // calculate p2 - p1
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abY = p2[1] - p1[1];
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abZ = p2[2] - p1[2];
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acX = p3[0] - p1[0]; // calculate p3 - p1
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acY = p3[1] - p1[1];
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acZ = p3[2] - p1[2];
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crossX = (abY * acZ) - (abZ * acY); // get cross product
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crossY = (abZ * acX) - (abX * acZ); // (p2 - p1) X (p3 - p1)
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crossZ = (abX * acY) - (abY * acX);
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sqrLength = (crossX * crossX) + (crossY * crossY) +
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(crossZ * crossZ);
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if (sqrLength > ZERO_EPS)
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invLength = (float) (1.0 / sqrt(sqrLength));
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else
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invLength = 1.0f;
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norm[0] = crossX * invLength;
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norm[1] = crossY * invLength;
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norm[2] = crossZ * invLength;
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}
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