server_clip.c revision e0e0c19eefceaf5d4ec40f9466b58a771f50e799
/* Copyright (c) 2001, Stanford University
* All rights reserved
*
* See the file LICENSE.txt for information on redistributing this software.
*/
/*
* This code contributed by Karl Rasche <rkarl@vr.clemson.edu>
*/
#include <math.h>
#include "cr_server.h"
#include "cr_mem.h"
#include "server.h"
static void
__find_intersection(double *s, double *e, double *clp, double *clp_next,
double *intr)
{
double v1[2], v2[2];
double A, B, T;
v1[0] = e[0] - s[0];
v1[1] = e[1] - s[1];
v2[0] = clp_next[0] - clp[0];
v2[1] = clp_next[1] - clp[1];
if ((v1[1]) && (v2[0]))
{
A = (clp[1]-s[1])/v1[1] + (v2[1]/v1[1])*(s[0]-clp[0])/v2[0];
B = 1.-(v2[1]/v1[1])*(v1[0]/v2[0]);
if (B)
T = A/B;
else
{
T = 0;
}
intr[0] = s[0]+T*v1[0];
intr[1] = s[1]+T*v1[1];
}
else
if (v1[1])
{
/* clp -> clp_next is vertical */
T = (clp[0]-s[0])/v1[0];
intr[0] = s[0]+T*v1[0];
intr[1] = s[1]+T*v1[1];
}
else
{
/* s -> e is horizontal */
T = (s[1]-clp[1])/v2[1];
intr[0] = clp[0]+T*v2[0];
intr[1] = clp[1]+T*v2[1];
}
}
static void
__clip_one_side(double *poly, int npnts, double *clp, double *clp_next,
double *norm,
double **new_poly_in, int *new_npnts_in,
double **new_poly_out, int *new_npnts_out)
{
int a, sin, ein;
double *s, *e, intr[2];
*new_poly_in = (double *)crAlloc(2*npnts*2*sizeof(double));
*new_npnts_in = 0;
*new_poly_out = (double *)crAlloc(2*npnts*2*sizeof(double));
*new_npnts_out = 0;
s = poly;
for (a=0; a<npnts; a++)
{
e = poly+2*((a+1)%npnts);
if (((e[0]-clp[0])*norm[0]) + ((e[1]-clp[1])*norm[1]) >= 0)
ein = 0;
else
ein = 1;
if (((s[0]-clp[0])*norm[0]) + ((s[1]-clp[1])*norm[1]) >= 0)
sin = 0;
else
sin = 1;
if (sin && ein)
{
/* case 1: */
crMemcpy(*new_poly_in+2*(*new_npnts_in), e, 2*sizeof(double));
(*new_npnts_in)++;
}
else
if (sin && (!ein))
{
/* case 2: */
__find_intersection(s, e, clp, clp_next, intr);
crMemcpy(*new_poly_in+2*(*new_npnts_in), intr, 2*sizeof(double));
(*new_npnts_in)++;
crMemcpy(*new_poly_out+2*(*new_npnts_out), intr, 2*sizeof(double));
(*new_npnts_out)++;
crMemcpy(*new_poly_out+2*(*new_npnts_out), e, 2*sizeof(double));
(*new_npnts_out)++;
}
else
if ((!sin) && ein)
{
/* case 4: */
__find_intersection(s, e, clp, clp_next, intr);
crMemcpy((*new_poly_in)+2*(*new_npnts_in), intr, 2*sizeof(double));
(*new_npnts_in)++;
crMemcpy((*new_poly_in)+2*(*new_npnts_in), e, 2*sizeof(double));
(*new_npnts_in)++;
crMemcpy(*new_poly_out+2*(*new_npnts_out), intr, 2*sizeof(double));
(*new_npnts_out)++;
}
else
{
crMemcpy(*new_poly_out+2*(*new_npnts_out), e, 2*sizeof(double));
(*new_npnts_out)++;
}
s = e;
}
}
/*
* Sutherland/Hodgman clipping for interior & exterior regions.
* length_of((*new_vert_out)[a]) == nclip_to_vert
*/
static void
__clip(double *poly, int nvert, double *clip_to_poly, int nclip_to_vert,
double **new_vert_in, int *nnew_vert_in,
double ***new_vert_out, int **nnew_vert_out)
{
int a, side, *nout;
double *clip_normals, *s, *e, *n, *new_vert_src;
double *norm, *clp, *clp_next;
double **out;
*new_vert_out = (double **)crAlloc(nclip_to_vert*sizeof(double *));
*nnew_vert_out = (int *)crAlloc(nclip_to_vert*sizeof(int));
/*
* First, compute normals for the clip poly. This
* breaks for multiple (3+) adjacent colinear verticies
*/
clip_normals = (double *)crAlloc(nclip_to_vert*2*sizeof(double));
for (a=0; a<nclip_to_vert; a++)
{
s = clip_to_poly+2*a;
e = clip_to_poly+2*((a+1)%nclip_to_vert);
n = clip_to_poly+2*((a+2)%nclip_to_vert);
norm = clip_normals+2*a;
norm[0] = e[1]-s[1];
norm[1] = -1*(e[0]-s[0]);
/*
* if dot(norm, n-e) > 0), the normals are backwards,
* assuming the clip region is convex
*/
if (norm[0]*(n[0]-e[0]) + norm[1]*(n[1]-e[1]) > 0)
{
norm[0] *= -1;
norm[1] *= -1;
}
}
new_vert_src = (double *)crAlloc(nvert*nclip_to_vert*2*sizeof(double));
crMemcpy(new_vert_src, poly, 2*nvert*sizeof(double));
for (side=0; side<nclip_to_vert; side++)
{
clp = clip_to_poly+2*side;
clp_next = clip_to_poly+2*((side+1)%nclip_to_vert);
norm = clip_normals+2*side;
*nnew_vert_in = 0;
nout = (*nnew_vert_out)+side;
out = (*new_vert_out)+side;
__clip_one_side(new_vert_src, nvert, clp, clp_next, norm,
new_vert_in, nnew_vert_in,
out, nout);
crMemcpy(new_vert_src, (*new_vert_in), 2*(*nnew_vert_in)*sizeof(double));
if (side != nclip_to_vert-1)
crFree(*new_vert_in);
nvert = *nnew_vert_in;
}
}
/*
* Given a bitmap and a group of 'base' polygons [the quads we are testing],
* perform the unions and differences specified by the map and return
* the resulting geometry
*/
static void
__execute_combination(CRPoly **base, int n, int *mask, CRPoly **head)
{
int a, b, got_intr;
int nin, *nout, last;
double *in, **out;
CRPoly *intr, *diff, *p;
*head = NULL;
intr = (CRPoly *)crAlloc(sizeof(CRPoly));
intr->next = NULL;
got_intr = 0;
/* first, intersect the first 2 polys marked */
for (a=0; a<n; a++)
if (mask[a]) break;
for (b=a+1; b<n; b++)
if (mask[b]) break;
__clip(base[a]->points, base[a]->npoints,
base[b]->points, base[b]->npoints,
&in, &nin, &out, &nout);
last = b;
crFree (nout);
for (a=0; a<base[last]->npoints; a++)
if (out[a])
crFree(out[a]);
crFree(out);
if (nin)
{
intr->npoints = nin;
intr->points = in;
got_intr = 1;
}
while (1)
{
for (a=last+1; a<n; a++)
if (mask[a]) break;
if (a == n) break;
if (got_intr)
{
__clip(base[a]->points, base[a]->npoints,
intr->points, intr->npoints,
&in, &nin, &out, &nout);
crFree (nout);
for (b=0; b<intr->npoints; b++)
if (out[b])
crFree(out[b]);
crFree(out);
if (nin)
{
intr->npoints = nin;
intr->points = in;
}
else
{
got_intr = 0;
break;
}
}
else
{
__clip(base[a]->points, base[a]->npoints,
base[last]->points, base[last]->npoints,
&in, &nin, &out, &nout);
crFree (nout);
for (b=0; b<base[last]->npoints; b++)
{
if (out[b])
crFree(out[b]);
}
crFree(out);
if (nin)
{
intr->npoints = nin;
intr->points = in;
got_intr = 1;
}
}
last = a;
if (a == n) break;
}
/* can't subract something from nothing! */
if (got_intr)
*head = intr;
else
return;
/* find the first item to subtract */
for (a=0; a<n; a++)
if (!mask[a]) break;
if (a == n) return;
last = a;
/* and subtract it */
diff = NULL;
__clip(intr->points, intr->npoints,
base[last]->points, base[last]->npoints,
&in, &nin, &out, &nout);
crFree(in);
for (a=0; a<base[last]->npoints; a++)
{
if (!nout[a]) continue;
p = (CRPoly *)crAlloc(sizeof(CRPoly));
p->npoints = nout[a];
p->points = out[a];
p->next = diff;
diff = p;
}
*head = diff;
while (1)
{
intr = diff;
diff = NULL;
for (a=last+1; a<n; a++)
if (!mask[a]) break;
if (a == n) return;
last = a;
/* subtract mask[a] from everything in intr and
* plop it into diff */
while (intr)
{
__clip(intr->points, intr->npoints,
base[last]->points, base[last]->npoints,
&in, &nin, &out, &nout);
crFree(in);
for (a=0; a<base[last]->npoints; a++)
{
if (!nout[a]) continue;
p = (CRPoly *)crAlloc(sizeof(CRPoly));
p->npoints = nout[a];
p->points = out[a];
p->next = diff;
diff = p;
}
intr = intr->next;
}
*head = diff;
}
}
/*
* Here we generate all valid bitmaps to represent union/difference
* conbinations. Each bitmap is N elements long, where N is the
* number of polys [quads] that we are testing for overlap
*/
static void
__generate_masks(int n, int ***mask, int *nmasks)
{
int a, b, c, d, e;
int i, idx, isec_size, add;
*mask = (int **)crAlloc((unsigned int)pow(2, n)*sizeof(int));
for (a=0; a<pow(2, n); a++)
(*mask)[a] = (int *)crAlloc(n*sizeof(int));
/* compute combinations */
idx = 0;
for (isec_size=1; isec_size<n; isec_size++)
{
for (a=0; a<n; a++)
{
for (b=a+1; b<n; b++)
{
crMemset((*mask)[idx], 0, n*sizeof(int));
(*mask)[idx][a] = 1;
add = 1;
for (c=0; c<isec_size; c++)
{
i = (b+c) % n;
if (i == a) add = 0;
(*mask)[idx][i] = 1;
}
/* dup check */
if ((add) && (idx))
{
for (d=0; d<idx; d++)
{
add = 0;
for (e=0; e<n; e++)
{
if ((*mask)[idx][e] != (*mask)[d][e])
add = 1;
}
if (!add)
break;
}
}
if (add)
idx++;
}
}
}
*nmasks = idx;
}
/*
* To compute the overlap between a series of quads (This should work
* for n-gons, but we'll only need quads..), first generate a series of
* bitmaps that represent which elements to union together, and which
* to difference. This goes into 'mask'. We then evaluate each bitmap with
* Sutherland-Hodgman clipping to find the interior (union) and exterior
* (difference) regions.
*
* In the map, 1 == union, 0 == difference
*
* (*res)[a] is the head of a poly list for all the polys that conver
* regions of overlap between a+1 polys ((*res)[0] == NULL)
*/
void
crComputeOverlapGeom(double *quads, int nquad, CRPoly ***res)
{
int a, b, idx, isec_size, **mask;
CRPoly *p, *next, **base;
base = (CRPoly **)crAlloc(nquad*sizeof(CRPoly *));
for (a=0; a<nquad; a++)
{
p = (CRPoly *)crAlloc(sizeof(CRPoly));
p->npoints = 4;
p->points = (double *)crAlloc(8*sizeof(double));
for (b=0; b<8; b++)
{
p->points[b] = quads[8*a+b];
}
p->next = NULL;
base[a] = p;
}
*res = (CRPoly **)crAlloc(nquad*sizeof(CRPoly *));
for (a=0; a<nquad; a++)
(*res)[a] = NULL;
__generate_masks(nquad, &mask, &idx);
for (a=0; a<idx; a++)
{
isec_size = 0;
for (b=0; b<nquad; b++)
if (mask[a][b]) isec_size++;
isec_size--;
__execute_combination(base, nquad, mask[a], &p);
while (p)
{
next = p->next;
p->next = (*res)[isec_size];
(*res)[isec_size] = p;
p = next;
}
}
for (a=0; a<nquad; a++)
{
crFree(base[a]->points);
crFree(base[a]);
}
crFree(base);
}
/*
* This is similar to ComputeOverlapGeom above, but for "knockout"
* edge blending.
*
* my_quad_idx is an index of quads indicating which display tile
* we are computing geometry for. From this, we either generate
* geometry, or not, such that all geometry can be drawn in black
* and only one tile will show through the blend as non-black.
*
* To add a combination to our set of geom, we must test that:
* + mask[a][my_quad_idx] is set
* + mask[a][my_quad_idx] is not the first element set in
* mask[a].
* If these conditions hold, execute mask[a] and draw the resulting
* geometry in black
*
* Unlike ComputeOverlapGeom, res is just a list of polys to draw in black
*/
void
crComputeKnockoutGeom(double *quads, int nquad, int my_quad_idx, CRPoly **res)
{
int a, b, idx, first, **mask;
CRPoly *p, *next, **base;
base = (CRPoly **) crAlloc(nquad*sizeof(CRPoly *));
for (a=0; a<nquad; a++)
{
p = (CRPoly *) crAlloc(sizeof(CRPoly));
p->npoints = 4;
p->points = (double *) crAlloc(8*sizeof(double));
for (b=0; b<8; b++)
{
p->points[b] = quads[8*a+b];
}
p->next = NULL;
base[a] = p;
}
(*res) = NULL;
__generate_masks(nquad, &mask, &idx);
for (a=0; a<idx; a++)
{
/* test for above conditions */
if (!mask[a][my_quad_idx]) continue;
first = -1;
for (b=0; b<nquad; b++)
if (mask[a][b])
{
first = b;
break;
}
if (first == my_quad_idx) continue;
__execute_combination(base, nquad, mask[a], &p);
while (p)
{
next = p->next;
p->next = *res;
*res = p;
p = next;
}
}
for (a=0; a<nquad; a++)
{
crFree(base[a]->points);
crFree(base[a]);
}
crFree(base);
}