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/*
* affine.c -- Affine Transforms for 2d objects
* Copyright (C) 2002 Charles Yates <charles.yates@pandora.be>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#include "affine.h"
static inline void Multiply( affine_transform_t *this, affine_transform_t *that )
{
double output[2][2];
register int i, j;
for ( i = 0; i < 2; i ++ )
for ( j = 0; j < 2; j ++ )
output[ i ][ j ] = this->matrix[ i ][ 0 ] * that->matrix[ j ][ 0 ] +
this->matrix[ i ][ 1 ] * that->matrix[ j ][ 1 ];
this->matrix[ 0 ][ 0 ] = output[ 0 ][ 0 ];
this->matrix[ 0 ][ 1 ] = output[ 0 ][ 1 ];
this->matrix[ 1 ][ 0 ] = output[ 1 ][ 0 ];
this->matrix[ 1 ][ 1 ] = output[ 1 ][ 1 ];
}
void affine_transform_init( affine_transform_t *this )
{
this->matrix[ 0 ][ 0 ] = 1;
this->matrix[ 0 ][ 1 ] = 0;
this->matrix[ 1 ][ 0 ] = 0;
this->matrix[ 1 ][ 1 ] = 1;
}
// Rotate by a given angle
void affine_transform_rotate( affine_transform_t *this, double angle )
{
affine_transform_t affine;
affine.matrix[ 0 ][ 0 ] = cos( angle * M_PI / 180 );
affine.matrix[ 0 ][ 1 ] = 0 - sin( angle * M_PI / 180 );
affine.matrix[ 1 ][ 0 ] = sin( angle * M_PI / 180 );
affine.matrix[ 1 ][ 1 ] = cos( angle * M_PI / 180 );
Multiply( this, &affine );
}
// Shear by a given value
void affine_transform_shear( affine_transform_t *this, double shear )
{
affine_transform_t affine;
affine.matrix[ 0 ][ 0 ] = 1;
affine.matrix[ 0 ][ 1 ] = shear;
affine.matrix[ 1 ][ 0 ] = 0;
affine.matrix[ 1 ][ 1 ] = 1;
Multiply( this, &affine );
}
void affine_transform_scale( affine_transform_t *this, double sx, double sy )
{
affine_transform_t affine;
affine.matrix[ 0 ][ 0 ] = sx;
affine.matrix[ 0 ][ 1 ] = 0;
affine.matrix[ 1 ][ 0 ] = 0;
affine.matrix[ 1 ][ 1 ] = sy;
Multiply( this, &affine );
}
// Obtain the mapped x coordinate of the input
double affine_transform_mapx( affine_transform_t *this, int x, int y )
{
return this->matrix[0][0] * x + this->matrix[0][1] * y;
}
// Obtain the mapped y coordinate of the input
double affine_transform_mapy( affine_transform_t *this, int x, int y )
{
return this->matrix[1][0] * x + this->matrix[1][1] * y;
}
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