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Add the geopoly_regular(X,Y,R,N) function to the geopoly extension.

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FossilOrigin-Name: 4505bbae58357eacab262b642b2a56d6dd380de72faceb5bbfd042eb94a12c06
This commit is contained in:
drh
2018-09-28 14:01:17 +00:00
parent 601c8f2829
commit 60afcb80ee
4 changed files with 80 additions and 8 deletions
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59
ext/rtree/geopoly.c
View File

@ -486,6 +486,64 @@ static void geopolyAreaFunc(
}
}
#define GEOPOLY_PI 3.1415926535897932385
/* Fast approximation for cosine(X) for X between -0.5*pi and 2*pi
*/
static double geopolyCosine(double r){
assert( r>=-0.5*GEOPOLY_PI && r<=2.0*GEOPOLY_PI );
if( r>=1.5*GEOPOLY_PI ){
r -= 2.0*GEOPOLY_PI;
}
if( r>=0.5*GEOPOLY_PI ){
return -geopolyCosine(r-GEOPOLY_PI);
}else{
double r2 = r*r;
double r3 = r2*r;
double r5 = r3*r2;
return 0.9996949*r - 0.1656700*r3 + 0.0075134*r5;
}
}
/*
** Function: geopoly_regular(X,Y,R,N)
**
** Construct a simple, convex, regular polygon centered at X, Y
** with circumradius R and with N sides.
*/
static void geopolyRegularFunc(
sqlite3_context *context,
int argc,
sqlite3_value **argv
){
double x = sqlite3_value_double(argv[0]);
double y = sqlite3_value_double(argv[1]);
double r = sqlite3_value_double(argv[2]);
int n = sqlite3_value_int(argv[3]);
int i;
GeoPoly *p;
if( n<3 || r<=0.0 ) return;
if( n>1000 ) n = 1000;
p = sqlite3_malloc64( sizeof(*p) + (n-1)*2*sizeof(GeoCoord) );
if( p==0 ){
sqlite3_result_error_nomem(context);
return;
}
i = 1;
p->hdr[0] = *(unsigned char*)&i;
p->hdr[1] = 0;
p->hdr[2] = (n>>8)&0xff;
p->hdr[3] = n&0xff;
for(i=0; i<n; i++){
double rAngle = 2.0*GEOPOLY_PI*i/n;
p->a[i*2] = x - r*geopolyCosine(rAngle-0.5*GEOPOLY_PI);
p->a[i*2+1] = y + r*geopolyCosine(rAngle);
}
sqlite3_result_blob(context, p->hdr, 4+8*n, SQLITE_TRANSIENT);
sqlite3_free(p);
}
/*
** If pPoly is a polygon, compute its bounding box. Then:
**
@ -1654,6 +1712,7 @@ static int sqlite3_geopoly_init(sqlite3 *db){
{ geopolyDebugFunc, 1, 0, "geopoly_debug" },
{ geopolyBBoxFunc, 1, 1, "geopoly_bbox" },
{ geopolyXformFunc, 7, 1, "geopoly_xform" },
{ geopolyRegularFunc, 4, 1, "geopoly_regular" },
};
static const struct {
void (*xStep)(sqlite3_context*,int,sqlite3_value**);

13
ext/rtree/visual01.txt
View File

@ -586,4 +586,17 @@ SELECT geopoly_svg(poly,'style="fill:none;stroke:black;stroke-width:2"')
ROLLBACK;
.print '</svg>'
.print '<h1>Regular Polygons</h1>'
.print '<svg width="1000" height="200" style="border:1px solid black">'
SELECT geopoly_svg(geopoly_regular(100,100,40,3),'style="fill:none;stroke:red;stroke-width:1"');
SELECT geopoly_svg(geopoly_regular(200,100,40,4),'style="fill:none;stroke:orange;stroke-width:1"');
SELECT geopoly_svg(geopoly_regular(300,100,40,5),'style="fill:none;stroke:green;stroke-width:1"');
SELECT geopoly_svg(geopoly_regular(400,100,40,6),'style="fill:none;stroke:blue;stroke-width:1"');
SELECT geopoly_svg(geopoly_regular(500,100,40,7),'style="fill:none;stroke:purple;stroke-width:1"');
SELECT geopoly_svg(geopoly_regular(600,100,40,8),'style="fill:none;stroke:red;stroke-width:1"');
SELECT geopoly_svg(geopoly_regular(700,100,40,10),'style="fill:none;stroke:orange;stroke-width:1"');
SELECT geopoly_svg(geopoly_regular(800,100,40,20),'style="fill:none;stroke:green;stroke-width:1"');
SELECT geopoly_svg(geopoly_regular(900,100,40,30),'style="fill:none;stroke:blue;stroke-width:1"');
.print '</svg>'
.print '</html>'