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/** \file
* Functions to/from NR::rotate.
*/
#include <glib.h>
#include "libnr/nr-rotate-ops.h"
#include "libnr/nr-rotate-fns.h"
/**
* Returns a rotation matrix corresponding by the specified angle about the origin.
*
* Angle direction in Inkscape code: If you use the traditional mathematics convention that y
* increases upwards, then positive angles are anticlockwise as per the mathematics convention. If
* you take the common non-mathematical convention that y increases downwards, then positive angles
* are clockwise, as is common outside of mathematics.
*/
NR::rotate
rotate_degrees(double degrees)
{
if (degrees < 0) {
return rotate_degrees(-degrees).inverse();
}
double const degrees0 = degrees;
if (degrees >= 360) {
degrees = fmod(degrees, 360);
}
NR::rotate ret(1., 0.);
if (degrees >= 180) {
NR::rotate const rot180(-1., 0.);
degrees -= 180;
ret = rot180;
}
if (degrees >= 90) {
NR::rotate const rot90(0., 1.);
degrees -= 90;
ret *= rot90;
}
if (degrees == 45) {
NR::rotate const rot45(M_SQRT1_2, M_SQRT1_2);
ret *= rot45;
} else {
double const radians = M_PI * ( degrees / 180 );
ret *= NR::rotate(cos(radians), sin(radians));
}
NR::rotate const raw_ret( M_PI * ( degrees0 / 180 ) );
g_return_val_if_fail(rotate_equalp(ret, raw_ret, 1e-8),
raw_ret);
return ret;
}
/*
Local Variables:
mode:c++
c-file-style:"stroustrup"
c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
indent-tabs-mode:nil
fill-column:99
End:
*/
// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4 :
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