lwiterator.c

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/**********************************************************************
 *
 * PostGIS - Spatial Types for PostgreSQL
 * http://postgis.net
 *
 * PostGIS 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.
 *
 * PostGIS 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 PostGIS.  If not, see <http://www.gnu.org/licenses/>.
 *
 **********************************************************************
 *
 * Copyright 2015 Daniel Baston <dbaston@gmail.com>
 *
 **********************************************************************/


#include "liblwgeom.h"
#include "lwgeom_log.h"

struct LISTNODE
{
        struct LISTNODE* next;
        void* item;
};
typedef struct LISTNODE LISTNODE;

/* The LWPOINTITERATOR consists of two stacks of items to process: a stack
 * of geometries, and a stack of POINTARRAYs extracted from those geometries.
 * The index "i" refers to the "next" point, which is found at the top of the
 * pointarrays stack.
 *
 * When the pointarrays stack is depleted, we pull a geometry from the geometry
 * stack to replenish it.
 */
struct LWPOINTITERATOR
{
        LISTNODE* geoms;
        LISTNODE* pointarrays;
        uint32_t i;
        char allow_modification;
};

static LISTNODE*
prepend_node(void* g, LISTNODE* front)
{
        LISTNODE* n = lwalloc(sizeof(LISTNODE));
        n->item = g;
        n->next = front;

        return n;
}

static LISTNODE*
pop_node(LISTNODE* i)
{
        LISTNODE* next = i->next;
        lwfree(i);
        return next;
}

static int
add_lwgeom_to_stack(LWPOINTITERATOR* s, LWGEOM* g)
{
        if (lwgeom_is_empty(g))
                return LW_FAILURE;

        s->geoms = prepend_node(g, s->geoms);
        return LW_SUCCESS;
}

static LISTNODE*
extract_pointarrays_from_lwgeom(LWGEOM* g)
{
        switch(lwgeom_get_type(g))
        {
        case POINTTYPE:
                return prepend_node(lwgeom_as_lwpoint(g)->point, NULL);
        case LINETYPE:
                return prepend_node(lwgeom_as_lwline(g)->points, NULL);
        case TRIANGLETYPE:
                return prepend_node(lwgeom_as_lwtriangle(g)->points, NULL);
        case CIRCSTRINGTYPE:
                return prepend_node(lwgeom_as_lwcircstring(g)->points, NULL);
        case POLYGONTYPE:
        {
                LISTNODE* n = NULL;

                LWPOLY* p = lwgeom_as_lwpoly(g);
                int i;
                for (i = p->nrings - 1; i >= 0; i--)
                {
                        n = prepend_node(p->rings[i], n);
                }

                return n;
        }
        default:
                lwerror("Unsupported geometry type for lwpointiterator");
        }

        return NULL;
}

static void
unroll_collection(LWPOINTITERATOR* s)
{
        int i;
        LWCOLLECTION* c;

        if (!s->geoms)
        {
                return;
        }

        c = (LWCOLLECTION*) s->geoms->item;
        s->geoms = pop_node(s->geoms);

        for (i = c->ngeoms - 1; i >= 0; i--)
        {
                LWGEOM* g = lwcollection_getsubgeom(c, i);

                add_lwgeom_to_stack(s, g);
        }
}

static void
unroll_collections(LWPOINTITERATOR* s)
{
        while(s->geoms && lwgeom_is_collection(s->geoms->item))
        {
                unroll_collection(s);
        }
}

static int
lwpointiterator_advance(LWPOINTITERATOR* s)
{
        s->i += 1;

        /* We've reached the end of our current POINTARRAY.  Try to see if there
         * are any more POINTARRAYS on the stack. */
        if (s->pointarrays && s->i >= ((POINTARRAY*) s->pointarrays->item)->npoints)
        {
                s->pointarrays = pop_node(s->pointarrays);
                s->i = 0;
        }

        /* We don't have a current POINTARRAY.  Pull a geometry from the stack, and
         * decompose it into its POINTARRARYs. */
        if (!s->pointarrays)
        {
                LWGEOM* g;
                unroll_collections(s);

                if (!s->geoms)
                {
                        return LW_FAILURE;
                }

                s->i = 0;
                g = s->geoms->item;
                s->pointarrays = extract_pointarrays_from_lwgeom(g);

                s->geoms = pop_node(s->geoms);
        }

        if (!s->pointarrays)
        {
                return LW_FAILURE;
        }
        return LW_SUCCESS;
}

/* Public API implementation */

int
lwpointiterator_peek(LWPOINTITERATOR* s, POINT4D* p)
{
        if (!lwpointiterator_has_next(s))
                return LW_FAILURE;

        return getPoint4d_p(s->pointarrays->item, s->i, p);
}

int
lwpointiterator_has_next(LWPOINTITERATOR* s)
{
        if (s->pointarrays && s->i < ((POINTARRAY*) s->pointarrays->item)->npoints)
                return LW_TRUE;
        return LW_FALSE;
}

int
lwpointiterator_next(LWPOINTITERATOR* s, POINT4D* p)
{
        if (!lwpointiterator_has_next(s))
                return LW_FAILURE;

        /* If p is NULL, just advance without reading */
        if (p && !lwpointiterator_peek(s, p))
                return LW_FAILURE;

        lwpointiterator_advance(s);
        return LW_SUCCESS;
}

int
lwpointiterator_modify_next(LWPOINTITERATOR* s, const POINT4D* p)
{
        if (!lwpointiterator_has_next(s))
                return LW_FAILURE;

        if (!s->allow_modification)
        {
                lwerror("Cannot write to read-only iterator");
                return LW_FAILURE;
        }

        ptarray_set_point4d(s->pointarrays->item, s->i, p);

        lwpointiterator_advance(s);
        return LW_SUCCESS;
}

LWPOINTITERATOR*
lwpointiterator_create(const LWGEOM* g)
{
        LWPOINTITERATOR* it = lwpointiterator_create_rw((LWGEOM*) g);
        it->allow_modification = LW_FALSE;

        return it;
}

LWPOINTITERATOR*
lwpointiterator_create_rw(LWGEOM* g)
{
        LWPOINTITERATOR* it = lwalloc(sizeof(LWPOINTITERATOR));

        it->geoms = NULL;
        it->pointarrays = NULL;
        it->i = 0;
        it->allow_modification = LW_TRUE;

        add_lwgeom_to_stack(it, g);
        lwpointiterator_advance(it);

        return it;
}

void
lwpointiterator_destroy(LWPOINTITERATOR* s)
{
        while (s->geoms != NULL)
        {
                s->geoms = pop_node(s->geoms);
        }

        while (s->pointarrays != NULL)
        {
                s->pointarrays = pop_node(s->pointarrays);
        }

        lwfree(s);
}