56 lines
1.8 KiB
C
56 lines
1.8 KiB
C
#include <c3d/maths.h>
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C3D_FQuat Quat_FromMtx(const C3D_Mtx* m)
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{
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//Taken from Gamasutra:
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//http://www.gamasutra.com/view/feature/131686/rotating_objects_using_quaternions.php
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//Expanded upon from:
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//http://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToQuaternion/
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//Variables we need.
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float trace, sqrtTrace;
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C3D_FQuat q;
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//Check the main diagonal of the passed-in matrix for positive/negative signs.
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trace = m->r[0].c[0] + m->r[1].c[1] + m->r[2].c[2];
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if (trace > 0.0f)
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{
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//Diagonal is positive.
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sqrtTrace = sqrtf(trace + 1.0f);
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q.w = sqrtTrace / 2.0f;
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sqrtTrace = 0.5 / sqrtTrace;
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q.x = (m->r[1].c[2] - m->r[2].c[1]) * sqrtTrace;
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q.y = (m->r[2].c[0] - m->r[0].c[2]) * sqrtTrace;
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q.z = (m->r[0].c[1] - m->r[1].c[0]) * sqrtTrace;
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}
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else
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{
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//Diagonal is negative or equals to zero. We need to identify which major diagonal element has the greatest value.
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if (m->r[0].c[0] > m->r[1].c[1] && m->r[0].c[0] > m->r[2].c[2])
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{
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sqrtTrace = 2.0f * sqrtf(1.0f + m->r[0].c[0] - m->r[1].c[1] - m->r[2].c[2]);
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q.w = (m->r[2].c[1] - m->r[1].c[2]) / sqrtTrace;
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q.x = 0.25f * sqrtTrace;
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q.y = (m->r[0].c[1] - m->r[1].c[0]) / sqrtTrace;
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q.z = (m->r[0].c[2] - m->r[2].c[0]) / sqrtTrace;
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}
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else if (m->r[1].c[1] > m->r[2].c[2])
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{
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sqrtTrace = 2.0f * sqrtf(1.0f + m->r[1].c[1] - m->r[0].c[0] - m->r[2].c[2]);
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q.w = (m->r[0].c[2] - m->r[2].c[0]) / sqrtTrace;
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q.x = (m->r[0].c[1] - m->r[1].c[0]) / sqrtTrace;
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q.y = 0.25f * sqrtTrace;
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q.z = (m->r[1].c[2] - m->r[2].c[1]) / sqrtTrace;
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}
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else
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{
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sqrtTrace = 2.0f * sqrtf(1.0f + m->r[2].c[2] - m->r[0].c[0] - m->r[1].c[1]);
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q.w = (m->r[1].c[0] - m->r[0].c[1]) / sqrtTrace;
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q.x = (m->r[0].c[2] - m->r[2].c[0]) / sqrtTrace;
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q.y = (m->r[1].c[2] - m->r[2].c[1]) / sqrtTrace;
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q.z = 0.25f * sqrtTrace;
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}
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}
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return q;
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}
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