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/* The GIMP -- an image manipulation program
* Copyright (C) 1995 Spencer Kimball and Peter Mattis
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#include "config.h"
#include <glib.h>
#include "libgimpmath/gimpmath.h"
#include "tools-utils.h"
/**
* gimp_tool_motion_constrain_helper:
* @dx: the (fixed) delta-x
* @dy: a suggested delta-y
*
* Returns an adjusted dy' near dy such that the slope (dx,dy')
* is a multiple of 15 degrees.
**/
static gdouble
gimp_tool_motion_constrain_helper (gdouble dx,
gdouble dy)
{
static const gdouble slope[4] = { 0, 0.26795, 0.57735, 1 };
static const gdouble divider[3] = { 0.13165, 0.41421, 0.76732 };
gint i;
if (dy < 0)
return - gimp_tool_motion_constrain_helper (dx, -dy);
dx = fabs (dx);
for (i = 0; i < 3; i ++)
if (dy < dx * divider[i])
break;
dy = dx * slope[i];
return dy;
}
/**
* gimp_tool_motion_constrain:
* @start_x:
* @start_y:
* @end_x:
* @end_y:
*
* Restricts the motion vector to 15 degree steps by changing the end
* point (if necessary).
**/
void
gimp_tool_motion_constrain (gdouble start_x,
gdouble start_y,
gdouble *end_x,
gdouble *end_y)
{
gdouble dx = *end_x - start_x;
gdouble dy = *end_y - start_y;
/* This algorithm changes only one of dx and dy, and does not try
* to constrain the resulting dx and dy to integers. This gives
* at least two benefits:
* 1. gimp_tool_motion_constrain is idempotent, even if followed by
* a rounding operation.
* 2. For any two lines with the same starting-point and ideal
* 15-degree direction, the points plotted by
* gimp_paint_core_interpolate for the shorter line will always
* be a superset of those plotted for the longer line.
*/
if (fabs (dx) > fabs (dy))
*end_y = (start_y + gimp_tool_motion_constrain_helper (dx, dy));
else
*end_x = (start_x + gimp_tool_motion_constrain_helper (dy, dx));
}
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