plaffine.c

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// Affine manipulation routines for PLplot.
//
// Copyright (C) 2009-2014 Alan W. Irwin
//
// This file is part of PLplot.
//
// PLplot is free software; you can redistribute it and/or modify
// it under the terms of the GNU Library General Public License as published
// by the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// PLplot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Library General Public License for more details.
//
// You should have received a copy of the GNU Library General Public License
// along with PLplot; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
//
//

#include "plplotP.h"

//

void
plP_affine_identity( PLFLT *affine_vector )
{
    affine_vector[0] = 1.;
    affine_vector[1] = 0.;
    affine_vector[2] = 0.;
    affine_vector[3] = 1.;
    affine_vector[4] = 0.;
    affine_vector[5] = 0.;
}

void
plP_affine_translate( PLFLT *affine_vector, PLFLT xtranslate, PLFLT ytranslate )
{
    affine_vector[0] = 1.;
    affine_vector[1] = 0.;
    affine_vector[2] = 0.;
    affine_vector[3] = 1.;
    // If the new coordinate system axis is shifted by xtranslate and ytranslate
    // relative to the old, then the actual new coordinates are shifted in
    // the opposite direction.
    affine_vector[4] = -xtranslate;
    affine_vector[5] = -ytranslate;
}

void
plP_affine_scale( PLFLT *affine_vector, PLFLT xscale, PLFLT yscale )
{
    // If the new coordinate system axes are scaled by xscale and yscale
    // relative to the old, then the actual new coordinates are scaled
    // by the inverses.
    if ( xscale == 0. )
    {
        plwarn( "plP_affine_scale: attempt to scale X coordinates by zero." );
        xscale = 1.;
    }
    if ( yscale == 0. )
    {
        plwarn( "plP_affine_scale: attempt to scale Y coordinates by zero." );
        yscale = 1.;
    }
    affine_vector[0] = 1. / xscale;
    affine_vector[1] = 0.;
    affine_vector[2] = 0.;
    affine_vector[3] = 1. / yscale;
    affine_vector[4] = 0.;
    affine_vector[5] = 0.;
}

void
plP_affine_rotate( PLFLT *affine_vector, PLFLT angle )
{
    PLFLT cosangle = cos( PI * angle / 180. );
    PLFLT sinangle = sin( PI * angle / 180. );
    affine_vector[0] = cosangle;
    affine_vector[1] = -sinangle;
    affine_vector[2] = sinangle;
    affine_vector[3] = cosangle;
    affine_vector[4] = 0.;
    affine_vector[5] = 0.;
}


void
plP_affine_xskew( PLFLT *affine_vector, PLFLT angle )
{
    PLFLT tanangle = tan( PI * angle / 180. );
    affine_vector[0] = 1.;
    affine_vector[1] = 0.;
    affine_vector[2] = -tanangle;
    affine_vector[3] = 1.;
    affine_vector[4] = 0.;
    affine_vector[5] = 0.;
}


void
plP_affine_yskew( PLFLT *affine_vector, PLFLT angle )
{
    PLFLT tanangle = tan( PI * angle / 180. );
    affine_vector[0] = 1.;
    affine_vector[1] = -tanangle;
    affine_vector[2] = 0.;
    affine_vector[3] = 1.;
    affine_vector[4] = 0.;
    affine_vector[5] = 0.;
}


void
plP_affine_multiply(
    PLFLT *affine_vectorA,
    PLFLT_VECTOR affine_vectorB,
    PLFLT_VECTOR affine_vectorC )
{
    int   i;
    PLFLT result[NAFFINE];
    // Multiply two affine matrices stored in affine vector form.
    result[0] = affine_vectorB[0] * affine_vectorC[0] +
                affine_vectorB[2] * affine_vectorC[1];
    result[2] = affine_vectorB[0] * affine_vectorC[2] +
                affine_vectorB[2] * affine_vectorC[3];
    result[4] = affine_vectorB[0] * affine_vectorC[4] +
                affine_vectorB[2] * affine_vectorC[5] +
                affine_vectorB[4];

    result[1] = affine_vectorB[1] * affine_vectorC[0] +
                affine_vectorB[3] * affine_vectorC[1];
    result[3] = affine_vectorB[1] * affine_vectorC[2] +
                affine_vectorB[3] * affine_vectorC[3];
    result[5] = affine_vectorB[1] * affine_vectorC[4] +
                affine_vectorB[3] * affine_vectorC[5] +
                affine_vectorB[5];

    for ( i = 0; i < NAFFINE; i++ )
        affine_vectorA[i] = result[i];
}