b3d9f313d4
This makes a change to the original point_in_poly algorithm from: http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html The aim was to tune the test so that tests against screen aligned rectangles are more resilient to some in-precision in how we transformed that rectangle into screen coordinates. In particular gnome-shell was finding that for some stage sizes then row 0 of the stage would become a dead zone when going through the software picking fast-path and this was because the y position of screen aligned rectangles could end up as something like 0.00024 and the way the algorithm works it doesn't have any epsilon/fuz factor to consider that in-precision. We've avoided introducing an epsilon factor to the comparisons since we feel there's a risk of changing some semantics in ways that might not be desirable. One of those is that if you transform two polygons which share an edge and test a point close to that edge then this algorithm will currently give a positive result for only one polygon. Another concern is the way this algorithm resolves the corner case where the horizontal ray being cast to count edge crossings may cross directly through a vertex. The solution is based on the "idea of Simulation of Simplicity" and "pretends to shift the ray infinitesimally down so that it either clearly intersects, or clearly doesn't touch". I'm not familiar with the idea myself so I expect a misplaced epsilon is likely to break that aspect of the algorithm. The simple solution this patch applies is to pixel align the polygon vertices which should eradicate most noise due to in-precision. https://bugzilla.gnome.org/show_bug.cgi?id=641197
100 lines
4.1 KiB
C
100 lines
4.1 KiB
C
/*
|
|
* Point Inclusion in Polygon Test
|
|
*
|
|
* Copyright (c) 1970-2003, Wm. Randolph Franklin
|
|
* Copyright (C) 2011 Intel Corporation.
|
|
*
|
|
* Permission is hereby granted, free of charge, to any person obtaining
|
|
* a copy of this software and associated documentation files (the
|
|
* "Software"), to deal in the Software without restriction, including
|
|
* without limitation the rights to use, copy, modify, merge, publish,
|
|
* distribute, sublicense, and/or sell copies of the Software, and to
|
|
* permit persons to whom the Software is furnished to do so, subject to
|
|
* the following conditions:
|
|
*
|
|
* 1. Redistributions of source code must retain the above copyright
|
|
* notice, this list of conditions and the following disclaimers.
|
|
* 2. Redistributions in binary form must reproduce the above
|
|
* copyright notice in the documentation and/or other materials
|
|
* provided with the distribution.
|
|
* 3. The name of W. Randolph Franklin may not be used to endorse or
|
|
* promote products derived from this Software without specific
|
|
* prior written permission.
|
|
*
|
|
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
|
|
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
|
|
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
|
|
* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
|
|
* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
|
|
* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
|
|
* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
|
|
*
|
|
* Note:
|
|
* The algorithm for this point_in_poly() function was learnt from:
|
|
* http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html
|
|
*/
|
|
|
|
#ifdef HAVE_CONFIG_H
|
|
#include "config.h"
|
|
#endif
|
|
|
|
#include "cogl-util.h"
|
|
|
|
#include <glib.h>
|
|
|
|
/* We've made a notable change to the original algorithm referenced
|
|
* above to make sure we have reliable results for screen aligned
|
|
* rectangles even though there may be some numerical in-precision in
|
|
* how the vertices of the polygon were calculated.
|
|
*
|
|
* We've avoided introducing an epsilon factor to the comparisons
|
|
* since we feel there's a risk of changing some semantics in ways that
|
|
* might not be desirable. One of those is that if you transform two
|
|
* polygons which share an edge and test a point close to that edge
|
|
* then this algorithm will currently give a positive result for only
|
|
* one polygon.
|
|
*
|
|
* Another concern is the way this algorithm resolves the corner case
|
|
* where the horizontal ray being cast to count edge crossings may
|
|
* cross directly through a vertex. The solution is based on the "idea
|
|
* of Simulation of Simplicity" and "pretends to shift the ray
|
|
* infinitesimally down so that it either clearly intersects, or
|
|
* clearly doesn't touch". I'm not familiar with the idea myself so I
|
|
* expect a misplaced epsilon is likely to break that aspect of the
|
|
* algorithm.
|
|
*
|
|
* The simple solution we've gone for is to pixel align the polygon
|
|
* vertices which should eradicate most noise due to in-precision.
|
|
*/
|
|
int
|
|
_cogl_util_point_in_screen_poly (float point_x,
|
|
float point_y,
|
|
void *vertices,
|
|
size_t stride,
|
|
int n_vertices)
|
|
{
|
|
int i, j, c = 0;
|
|
|
|
for (i = 0, j = n_vertices - 1; i < n_vertices; j = i++)
|
|
{
|
|
float vert_xi = *(float *)((guint8 *)vertices + i * stride);
|
|
float vert_xj = *(float *)((guint8 *)vertices + j * stride);
|
|
float vert_yi = *(float *)((guint8 *)vertices + i * stride +
|
|
sizeof (float));
|
|
float vert_yj = *(float *)((guint8 *)vertices + j * stride +
|
|
sizeof (float));
|
|
|
|
vert_xi = COGL_UTIL_NEARBYINT (vert_xi);
|
|
vert_xj = COGL_UTIL_NEARBYINT (vert_xj);
|
|
vert_yi = COGL_UTIL_NEARBYINT (vert_yi);
|
|
vert_yj = COGL_UTIL_NEARBYINT (vert_yj);
|
|
|
|
if (((vert_yi > point_y) != (vert_yj > point_y)) &&
|
|
(point_x < (vert_xj - vert_xi) * (point_y - vert_yi) /
|
|
(vert_yj - vert_yi) + vert_xi) )
|
|
c = !c;
|
|
}
|
|
|
|
return c;
|
|
}
|
|
|