1f0826543e
This adds a utility function that can determine if a given point intersects an arbitrary polygon, by counting how many edges a "semi-infinite" horizontal ray crosses from that point. The plan is to use this for a software based read-pixel fast path that avoids using the GPU to rasterize journaled primitives and can instead intersect a point being read with quads in the journal to determine the correct color.
70 lines
2.6 KiB
C
70 lines
2.6 KiB
C
/*
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* Point Inclusion in Polygon Test
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*
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* Copyright (c) 1970-2003, Wm. Randolph Franklin
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* Copyright (C) 2011 Intel Corporation.
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimers.
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* 2. Redistributions in binary form must reproduce the above
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* copyright notice in the documentation and/or other materials
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* provided with the distribution.
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* 3. The name of W. Randolph Franklin may not be used to endorse or
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* promote products derived from this Software without specific
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* prior written permission.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*
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* Note:
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* The algorithm for this point_in_poly() function was learnt from:
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* http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <glib.h>
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int
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_cogl_util_point_in_poly (float point_x,
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float point_y,
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void *vertices,
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size_t stride,
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int n_vertices)
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{
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int i, j, c = 0;
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for (i = 0, j = n_vertices - 1; i < n_vertices; j = i++)
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{
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float vert_xi = *(float *)((guint8 *)vertices + i * stride);
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float vert_xj = *(float *)((guint8 *)vertices + j * stride);
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float vert_yi = *(float *)((guint8 *)vertices + i * stride +
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sizeof (float));
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float vert_yj = *(float *)((guint8 *)vertices + j * stride +
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sizeof (float));
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if (((vert_yi > point_y) != (vert_yj > point_y)) &&
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(point_x < (vert_xj - vert_xi) * (point_y - vert_yi) /
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(vert_yj - vert_yi) + vert_xi) )
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c = !c;
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}
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return c;
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}
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