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From: kriso@northstar5 (Kris Olander)
Newsgroups: comp.windows.x
Subject: Using XPolygonRegion for getting pointer locations
Summary: Unclear on concept/usage of XPolygonRegion.
Keywords: XPolygonRegion
Message-ID: <23220@dartvax.Dartmouth.EDU>
Date: 18 Jul 90 00:42:57 GMT
Sender: news@dartvax.Dartmouth.EDU
Distribution: comp
Lines: 61

I'm creating a map.  I'm using XFillPolygon to display the countries, and
then I use XPolygonRegion to distinguish a the location of each country.

I'm under the assumption that I don't have to specify an offset using
XOffsetRegion if I want the drawable origin (the window that contains all
the countries) to be the regions origin.

After I've created all the countries and attached a 'Region' to each
country, I have been trapping Button1 'down' events as a means of selecting
a country.  I then go through the list of countries passing each
country's Region pointer into XPointInRegion to see which region the pointer
is trying to access.

The problem: none of my country's Regions ever match.  The Nut Shell books
give a whapping two pages describing Regions.

Can anyone clue me in?  Is this approach bogus?  I'd rather not dive into
the clipping algorithms for many sided polygons if X11 will do it for me.

Here's some of the code:
	} /* end Switch */
	for (i=0; i<geo->ncoords; i++) {
	    xy_array[i].x = (geo->coords[i]->x - bX ) / mX;
	    xy_array[i].y = (geo->coords[i]->y -bY ) / mY;
	}

	geo->locator = XPolygonRegion(xy_array, geo->ncoords,EvenOddRule);
	fprintf (stdout, "locator : %x \n", geo->locator);
------- and --------
DisplayRegion(window, button_event)
Window window;
XButtonEvent *button_event;
{
    GeoRegion *geo_check;
    int i, x, y;
    
    x = button_event->x; y = button_event->y;
 
    fprintf (stdout, "x, y: %d, %d\n", x, y);
    for (geo_check = First_region; 
	 geo_check != NULL;
	 geo_check = geo_check->next_region) {
	if(XPointInRegion(geo_check->locator,x, y))
	    break;
	fprintf (stdout, "region,locator: %s,%x\n",
		 geo_check->name, geo_check->locator);
    }
    if(geo_check)
	fprintf (stdout, "Region: %s\n", geo_check->name);
    else
	fprintf (stdout, "FAILED FINDING LOCATION OF POINTER\n");

}
----------------------- Sorry this is so long :( -------------------

				-Kris Olander

# Kris Olander ---- ---- arpa: Kris.Olander@Dartmouth.Edu    #
# ---------------------------------------------------------- #
# System Eng. Project NORTHSTAR                              #
# Thayer School of Eng., Dartmouth College                   #