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Enhancement: Mtx_Inverse() returns a non-zero determinant if the matrix passed in can be inverted, otherwise returns zero if the matrix is singular/degenerative.

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Thompson Lee 2016-08-05 01:18:03 -04:00 committed by Michael Theall
parent 0dcc009ae3
commit ae0ce14c9d
2 changed files with 10 additions and 9 deletions
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6
include/c3d/maths.h
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@ -299,11 +299,11 @@ void Mtx_Multiply(C3D_Mtx* out, const C3D_Mtx* a, const C3D_Mtx* b);
/** /**
* @brief Inverse a matrix * @brief Inverse a matrix
* @note returns 0.0f if the matrix is degenerate; i.e. no inverse
* @param[in,out] out Matrix to inverse * @param[in,out] out Matrix to inverse
* @retval true Matrix was inverted * @return determinant
* @retval false Matrix is degenerate
*/ */
bool Mtx_Inverse(C3D_Mtx* out); float Mtx_Inverse(C3D_Mtx* out);
/** /**
* @brief Multiply 3x3 matrix by a FVec3 * @brief Multiply 3x3 matrix by a FVec3

13
source/maths/mtx_inverse.c
View File

@ -1,8 +1,10 @@
#include <float.h> #include <float.h>
#include <c3d/maths.h> #include <c3d/maths.h>
bool Mtx_Inverse(C3D_Mtx* out) float Mtx_Inverse(C3D_Mtx* out)
{ {
//Mtx_Inverse can be used to calculate the determinant and the inverse of the matrix.
C3D_Mtx inv; C3D_Mtx inv;
float det; float det;
int i; int i;
@ -39,7 +41,8 @@ bool Mtx_Inverse(C3D_Mtx* out)
out->r[0].z * inv.r[2].x + out->r[0].w * inv.r[3].x; out->r[0].z * inv.r[2].x + out->r[0].w * inv.r[3].x;
if (fabsf(det) < FLT_EPSILON) if (fabsf(det) < FLT_EPSILON)
return false; //Returns 0.0f if we find the determinant is less than +/- FLT_EPSILON.
return 0.0f;
inv.r[0].y = -out->r[0].y * out->r[2].z * out->r[3].w + inv.r[0].y = -out->r[0].y * out->r[2].z * out->r[3].w +
out->r[0].y * out->r[2].w * out->r[3].z + out->r[0].y * out->r[2].w * out->r[3].z +
@ -125,10 +128,8 @@ bool Mtx_Inverse(C3D_Mtx* out)
out->r[2].x * out->r[0].y * out->r[1].z - out->r[2].x * out->r[0].y * out->r[1].z -
out->r[2].x * out->r[0].z * out->r[1].y; out->r[2].x * out->r[0].z * out->r[1].y;
det = 1.0 / det;
for (i = 0; i < 16; i++) for (i = 0; i < 16; i++)
out->m[i] = inv.m[i] * det; out->m[i] = inv.m[i] / det;
return true; return det;
} }