plgradient.c

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//      Implement linear gradients 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"

// To keep track of whether a sofware fallback warning has been issued.

static int foo;
// software fallback for gradient.
static void
plgradient_soft( PLINT n, PLFLT_VECTOR x, PLFLT_VECTOR y, PLFLT angle );

// define where plshades plots gradient for software fallback for
// gradient.

static PLINT
gradient_defined( PLFLT x, PLFLT y );

//--------------------------------------------------------------------------
// void plgradient()
//
// Draws a linear gradient at an angle relative to the increasing x
// direction for the polygon bounded by the x and y vertices.  x, and
// y are expressed in world coordinates, and angle (in the world
// coordinate system) is expressed in degrees.  The gradient is
// expressed using colour and transparency information from cmap1.  The
// geometrical gradient direction is specified by the angle argument.
// The 0. to 1. range of the independent variable of cmap1 corresponds
// to the range of the polygon in the direction specified by angle.
//--------------------------------------------------------------------------

void
c_plgradient( PLINT n, PLFLT_VECTOR x, PLFLT_VECTOR y, PLFLT angle )
{
    if ( plsc->level < 3 )
    {
        plabort( "plgradient: Please set up window first" );
        return;
    }
    if ( n < 3 )
    {
        plabort( "plgradient: Not enough vertices in polygon" );
        return;
    }

    if ( !plsc->dev_gradient )
    {
        if ( !foo )
        {
            plwarn( "Driver does not support native gradients, switching to software fallback gradient.\n" );
            foo = 1;
        }

        plgradient_soft( n, x, y, angle );
    }
    else
    {
      #define NGRAD    2
        int   i, irot_min;
        PLINT _xpoly[PL_MAXPOLY], _ypoly[PL_MAXPOLY];
        PLINT *xpoly, *ypoly;
        PLINT xgrad[NGRAD], ygrad[NGRAD], clpxmi, clpxma, clpymi, clpyma;
        PLFLT dxgrad[NGRAD], dygrad[NGRAD], xrot, xrot_min, xrot_max;
        PLINT npts;

        // Find (x1, y1) and (x2, y2) corresponding to beginning and end
        // of gradient vector.
        double cosangle = cos( PI * angle / 180. );
        double sinangle = sin( PI * angle / 180. );
        xrot     = x[0] * cosangle + y[0] * sinangle;
        xrot_min = xrot;
        xrot_max = xrot;
        irot_min = 0;
        for ( i = 1; i < n; i++ )
        {
            xrot = x[i] * cosangle + y[i] * sinangle;
            if ( xrot < xrot_min )
            {
                xrot_min = xrot;
                irot_min = i;
            }
            else if ( xrot > xrot_max )
            {
                xrot_max = xrot;
            }
        }
        // xrot_min and xrot_max are the minimum and maximum rotated x
        // coordinate of polygon vertices. Use the vertex corresponding
        // to the minimum  as the (xgrad[0], ygrad[0]) base of the
        // gradient vector, and calculate the (xgrad[1], ygrad[1]) tip of
        // the gradient vector from the range in rotated x coordinate and
        // the angle of the gradient.
        dxgrad[0] = x[irot_min];
        dxgrad[1] = dxgrad[0] + ( xrot_max - xrot_min ) * cosangle;
        dygrad[0] = y[irot_min];
        dygrad[1] = dygrad[0] + ( xrot_max - xrot_min ) * sinangle;
        for ( i = 0; i < NGRAD; i++ )
        {
            xgrad[i] = plP_wcpcx( dxgrad[i] );
            ygrad[i] = plP_wcpcy( dygrad[i] );
        }
        if ( plsc->difilt )
            difilt( xgrad, ygrad, NGRAD, &clpxmi, &clpxma, &clpymi, &clpyma );
        plsc->xgradient = xgrad;
        plsc->ygradient = ygrad;
        plsc->ngradient = NGRAD;

        npts = n;
        if ( n > PL_MAXPOLY - 1 )
        {
            xpoly = (PLINT *) malloc( (size_t) ( n + 1 ) * sizeof ( PLINT ) );
            ypoly = (PLINT *) malloc( (size_t) ( n + 1 ) * sizeof ( PLINT ) );

            if ( ( xpoly == NULL ) || ( ypoly == NULL ) )
            {
                plexit( "plgradient: Insufficient memory for large polygon" );
            }
        }
        else
        {
            xpoly = _xpoly;
            ypoly = _ypoly;
        }

        for ( i = 0; i < n; i++ )
        {
            xpoly[i] = plP_wcpcx( x[i] );
            ypoly[i] = plP_wcpcy( y[i] );
        }
        if ( x[0] != x[n - 1] || y[0] != y[n - 1] )
        {
            n++;
            xpoly[n - 1] = plP_wcpcx( x[0] );
            ypoly[n - 1] = plP_wcpcy( y[0] );
        }
        plP_plfclp( xpoly, ypoly, n, plsc->clpxmi, plsc->clpxma,
            plsc->clpymi, plsc->clpyma, plP_gradient );
        // Plot line corresponding to gradient to give visual
        // debugging cue.
        //plline( NGRAD, dxgrad, dygrad );

        // Check the original number of points
        if ( npts > PL_MAXPOLY - 1 )
        {
            free( xpoly );
            free( ypoly );
        }
    }
}

//--------------------------------------------------------------------------
// void plgradient_soft()
//
// Software fallback for gradient.  See c_plgradient for an explanation
// of the arguments.
//--------------------------------------------------------------------------

void
plgradient_soft( PLINT n, PLFLT_VECTOR x, PLFLT_VECTOR y, PLFLT angle )
{
    PLFLT xrot, xrot_min, xrot_max, cosangle, sinangle;
    PLFLT xmin, xmax, ymin, ymax;
    PLFLT **z, *edge, xcoord, ycoord;
    PLINT i, j;

    if ( n < 3 )
    {
        plabort( "plgradient_soft: Not enough vertices in polygon" );
        return;
    }


    // Define polygon boundary so it is accessible from gradient_defined.
    plsc->n_polygon = n;
    plsc->x_polygon = x;
    plsc->y_polygon = y;

    // Find x and y range of polygon.
    xmin = x[0];
    xmax = xmin;
    ymin = y[0];
    ymax = ymin;
    // Also find x range in rotated coordinate system where
    // xrot = x*cosangle + y*sinangle.
    cosangle = cos( PI / 180. * angle );
    sinangle = sin( PI / 180. * angle );
    xrot     = x[0] * cosangle + y[0] * sinangle;
    xrot_min = xrot;
    xrot_max = xrot;
    for ( i = 1; i < n; i++ )
    {
        if ( x[i] < xmin )
            xmin = x[i];
        else if ( x[i] > xmax )
            xmax = x[i];

        if ( y[i] < ymin )
            ymin = y[i];
        else if ( y[i] > ymax )
            ymax = y[i];

        xrot = x[i] * cosangle + y[i] * sinangle;
        if ( xrot < xrot_min )
            xrot_min = xrot;
        else if ( xrot > xrot_max )
            xrot_max = xrot;
    }

    // 2 x 2 array more than sufficient to define plane.
    // Temporarily use more to overcome irregular edge issue on defined
    // region.
    #define NX    20
    #define NY    20
    plAlloc2dGrid( &z, NX, NY );
    for ( i = 0; i < NX; i++ )
    {
        xcoord = xmin + ( (PLFLT) i ) * ( xmax - xmin ) / (PLFLT) ( NX - 1 );
        for ( j = 0; j < NY; j++ )
        {
            ycoord  = ymin + ( (PLFLT) j ) * ( ymax - ymin ) / (PLFLT) ( NY - 1 );
            xrot    = xcoord * cosangle + ycoord * sinangle;
            z[i][j] = ( xrot - xrot_min ) / ( xrot_max - xrot_min );
        }
    }
    // 101 edges gives reasonably smooth results for example 30.
    #define NEDGE    101
    // Define NEDGE shade edges (or NEDGE-1 shade levels)
    // from 0. to 1.
    if ( ( edge = (PLFLT *) malloc( NEDGE * sizeof ( PLFLT ) ) ) == NULL )
        plexit( "plgradient_soft: Insufficient memory for large polygon"
            );
    for ( i = 0; i < NEDGE; i++ )
        edge[i] = (PLFLT) i / (PLFLT) ( NEDGE - 1 );

    plshades( (PLFLT_MATRIX) z, NX, NY, gradient_defined, xmin, xmax, ymin, ymax,
        edge, NEDGE, 0, 0, 0, plfill, 1, NULL, NULL );
    free( (void *) edge );
    plFree2dGrid( z, NX, NY );
}

static PLINT
gradient_defined( PLFLT x, PLFLT y )
{
    return plP_pointinpolygon( plsc->n_polygon, plsc->x_polygon, plsc->y_polygon,
        x, y );
}