gv_quick.c

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/*!
   \file lib/ogsf/gv_quick.c
 
   \brief OGSF library -
 
   GRASS OpenGL gsurf OGSF Library
 
   Trying some stuff to draw a quick version of a vector map, to represent
   it when doing interactive translations.
 
   SPDX-FileCopyrightText: 1999-2008 GRASS Development Team
   SPDX-License-Identifier: GPL-2.0-or-later
 
   \author Bill Brown, USACERL (December 1993)
   \author Doxygenized by Martin Landa <landa.martin gmail.com> (May 2008)
 */
 
#include <stdio.h>
#include <stdlib.h>
 
#include <grass/gis.h>
#include <grass/ogsf.h>
 
#include "rowcol.h"
 
/*!
   \brief target number of desired points to represent entire file
 */
#define TFAST_PTS 800
 
/*!
   \brief max number of lines desired
 */
#define MFAST_LNS 400
 
static geoline *copy_line(geoline *);
static geoline *thin_line(geoline *, float);
 
/*!
   \brief Copy line
 
   \param gln source line (geoline)
 
   \return pointer to geoline struct
   \return on failure
 */
static geoline *copy_line(geoline *gln)
{
    geoline *newln;
    int i, np;
 
    newln = (geoline *)G_malloc(sizeof(geoline)); /* G_fatal_error */
    if (!newln) {
        return (NULL);
    }
 
    np = newln->npts = gln->npts;
 
    if (2 == (newln->dims = gln->dims)) {
        newln->p2 = (Point2 *)G_calloc(np, sizeof(Point2)); /* G_fatal_error */
        if (!newln->p2) {
            return (NULL);
        }
 
        for (i = 0; i < np; i++) {
            newln->p2[i][X] = gln->p2[i][X];
            newln->p2[i][Y] = gln->p2[i][Y];
        }
    }
    else {
        newln->p3 = (Point3 *)G_calloc(np, sizeof(Point3)); /* G_fatal_error */
        if (!newln->p3) {
            return (NULL);
        }
 
        for (i = 0; i < np; i++) {
            newln->p3[i][X] = gln->p3[i][X];
            newln->p3[i][Y] = gln->p3[i][Y];
            newln->p3[i][Z] = gln->p3[i][Z];
        }
    }
 
    newln->next = NULL;
 
    return (newln);
}
 
/*!
   \brief Thin line
 
   For now, just eliminate points at regular interval
 
   \param gln line (geoline)
   \param factor
 
   \return pointer to geoline struct
   \return NULL on failure
 */
static geoline *thin_line(geoline *gln, float factor)
{
    geoline *newln;
    int i, nextp, targp;
 
    newln = (geoline *)G_malloc(sizeof(geoline)); /* G_fatal_error */
    if (!newln) {
        return (NULL);
    }
 
    targp = (int)(gln->npts / factor);
 
    if (targp < 2) {
        targp = 2;
    }
 
    newln->npts = targp;
 
    if (2 == (newln->dims = gln->dims)) {
        newln->p2 =
            (Point2 *)G_calloc(targp, sizeof(Point2)); /* G_fatal_error */
        if (!newln->p2) {
            return (NULL);
        }
 
        for (i = 0; i < targp; i++) {
            if (i == targp - 1) {
                nextp = gln->npts - 1; /* avoid rounding error */
            }
            else {
                nextp = (int)((i * (gln->npts - 1)) / (targp - 1));
            }
 
            newln->p2[i][X] = gln->p2[nextp][X];
            newln->p2[i][Y] = gln->p2[nextp][Y];
        }
    }
    else {
        newln->p3 =
            (Point3 *)G_calloc(targp, sizeof(Point3)); /* G_fatal_error */
        if (!newln->p3) {
            return (NULL);
        }
 
        for (i = 0; i < targp; i++) {
            if (i == targp - 1) {
                nextp = gln->npts - 1; /* avoid rounding error */
            }
            else {
                nextp = (int)((i * (gln->npts - 1)) / (targp - 1));
            }
 
            newln->p3[i][X] = gln->p3[nextp][X];
            newln->p3[i][Y] = gln->p3[nextp][Y];
            newln->p3[i][Z] = gln->p3[nextp][Z];
        }
    }
 
    newln->next = NULL;
 
    return (newln);
}
 
/*!
   \brief Get line width
 
   \param gln line (geoline)
 
   \return line width
 */
float gv_line_length(geoline *gln)
{
    int n;
    float length = 0.0;
 
    for (n = 0; n < gln->npts - 1; n++) {
        if (gln->p2) {
            length += GS_P2distance(gln->p2[n + 1], gln->p2[n]);
        }
        else {
            length += GS_distance(gln->p3[n + 1], gln->p3[n]);
        }
    }
 
    return (length);
}
 
/*!
   \brief Get number of line vertices
 
   \param gln line (geoline)
 
   \return number of vertices
 */
int gln_num_points(geoline *gln)
{
    int np = 0;
    geoline *tln;
 
    for (tln = gln; tln; tln = tln->next) {
        np += tln->npts;
    }
 
    return (np);
}
 
/*!
   \brief Get number of points in vector
 
   \param gv vector (geovect)
 
   \return number of points
 */
int gv_num_points(geovect *gv)
{
    return (gln_num_points(gv->lines));
}
 
/*!
   \brief Decimate line
 
   strategy here: if line has more than average number of points, decimate
   by eliminating points, otherwise decimate by eliminating shorter lines
 
   \param gv vector (geovect)
 
   \return
 */
int gv_decimate_lines(geovect *gv)
{
    int T_pts, A_ppl, N_s;
    float decim_factor, slength[MFAST_LNS], T_slength, A_slength;
    geoline *gln, *prev;
 
    /* should check if already exists & free if != gv->lines */
    if (TFAST_PTS > (T_pts = gv_num_points(gv))) {
        gv->fastlines = gv->lines;
 
        return (1);
    }
 
    N_s = 0;
    T_slength = 0.0;
    decim_factor = T_pts / TFAST_PTS;
    A_ppl = T_pts / gv->n_lines; /* (int) Average points per line */
 
    prev = NULL;
 
    for (gln = gv->lines; gln; gln = gln->next) {
        if (gln->npts > A_ppl) {
            if (prev) {
                prev->next = thin_line(gln, decim_factor);
                prev = prev->next;
            }
            else {
                prev = gv->fastlines = thin_line(gln, decim_factor);
            }
        }
        else if (N_s < MFAST_LNS) {
            T_slength += slength[N_s++] = gv_line_length(gln);
        }
    }
 
    A_slength = T_slength / N_s;
    N_s = 0;
 
    for (gln = gv->lines; gln; gln = gln->next) {
        if (gln->npts <= A_ppl) {
            if (N_s < MFAST_LNS) {
                if (slength[N_s++] > A_slength) {
                    if (prev) {
                        prev->next = copy_line(gln);
                        prev = prev->next;
                    }
                    else {
                        prev = gv->fastlines = copy_line(gln);
                    }
                }
            }
        }
    }
 
    G_debug(3, "Decimated lines have %d points.",
            gln_num_points(gv->fastlines));
 
    return (1);
}