/usr/include/mapnik/agg/agg_span_gouraud_gray.h is in libmapnik-dev 2.2.0+ds1-6build2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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// Anti-Grain Geometry - Version 2.4
// Copyright (C) 2002-2005 Maxim Shemanarev (http://www.antigrain.com)
//
// Permission to copy, use, modify, sell and distribute this software
// is granted provided this copyright notice appears in all copies.
// This software is provided "as is" without express or implied
// warranty, and with no claim as to its suitability for any purpose.
//
//----------------------------------------------------------------------------
// Contact: mcseem@antigrain.com
// mcseemagg@yahoo.com
// http://www.antigrain.com
//----------------------------------------------------------------------------
//
// Adaptation for high precision colors has been sponsored by
// Liberty Technology Systems, Inc., visit http://lib-sys.com
//
// Liberty Technology Systems, Inc. is the provider of
// PostScript and PDF technology for software developers.
//
//----------------------------------------------------------------------------
#ifndef AGG_SPAN_GOURAUD_GRAY_INCLUDED
#define AGG_SPAN_GOURAUD_GRAY_INCLUDED
#include "agg_basics.h"
#include "agg_color_gray.h"
#include "agg_dda_line.h"
#include "agg_span_gouraud.h"
namespace agg
{
//=======================================================span_gouraud_gray
template<class ColorT> class span_gouraud_gray : public span_gouraud<ColorT>
{
public:
typedef ColorT color_type;
typedef typename color_type::value_type value_type;
typedef span_gouraud<color_type> base_type;
typedef typename base_type::coord_type coord_type;
enum subpixel_scale_e
{
subpixel_shift = 4,
subpixel_scale = 1 << subpixel_shift
};
private:
//--------------------------------------------------------------------
struct gray_calc
{
void init(const coord_type& c1, const coord_type& c2)
{
m_x1 = c1.x - 0.5;
m_y1 = c1.y - 0.5;
m_dx = c2.x - c1.x;
double dy = c2.y - c1.y;
m_1dy = (fabs(dy) < 1e-10) ? 1e10 : 1.0 / dy;
m_v1 = c1.color.v;
m_a1 = c1.color.a;
m_dv = c2.color.v - m_v1;
m_da = c2.color.a - m_a1;
}
void calc(double y)
{
double k = (y - m_y1) * m_1dy;
if(k < 0.0) k = 0.0;
if(k > 1.0) k = 1.0;
m_v = m_v1 + iround(m_dv * k);
m_a = m_a1 + iround(m_da * k);
m_x = iround((m_x1 + m_dx * k) * subpixel_scale);
}
double m_x1;
double m_y1;
double m_dx;
double m_1dy;
int m_v1;
int m_a1;
int m_dv;
int m_da;
int m_v;
int m_a;
int m_x;
};
public:
//--------------------------------------------------------------------
span_gouraud_gray() {}
span_gouraud_gray(const color_type& c1,
const color_type& c2,
const color_type& c3,
double x1, double y1,
double x2, double y2,
double x3, double y3,
double d = 0) :
base_type(c1, c2, c3, x1, y1, x2, y2, x3, y3, d)
{}
//--------------------------------------------------------------------
void prepare()
{
coord_type coord[3];
base_type::arrange_vertices(coord);
m_y2 = int(coord[1].y);
m_swap = cross_product(coord[0].x, coord[0].y,
coord[2].x, coord[2].y,
coord[1].x, coord[1].y) < 0.0;
m_c1.init(coord[0], coord[2]);
m_c2.init(coord[0], coord[1]);
m_c3.init(coord[1], coord[2]);
}
//--------------------------------------------------------------------
void generate(color_type* span, int x, int y, unsigned len)
{
m_c1.calc(y);
const gray_calc* pc1 = &m_c1;
const gray_calc* pc2 = &m_c2;
if(y < m_y2)
{
// Bottom part of the triangle (first subtriangle)
//-------------------------
m_c2.calc(y + m_c2.m_1dy);
}
else
{
// Upper part (second subtriangle)
//-------------------------
m_c3.calc(y - m_c3.m_1dy);
pc2 = &m_c3;
}
if(m_swap)
{
// It means that the triangle is oriented clockwise,
// so that we need to swap the controlling structures
//-------------------------
const gray_calc* t = pc2;
pc2 = pc1;
pc1 = t;
}
// Get the horizontal length with subpixel accuracy
// and protect it from division by zero
//-------------------------
int nlen = abs(pc2->m_x - pc1->m_x);
if(nlen <= 0) nlen = 1;
dda_line_interpolator<14> v(pc1->m_v, pc2->m_v, nlen);
dda_line_interpolator<14> a(pc1->m_a, pc2->m_a, nlen);
// Calculate the starting point of the gradient with subpixel
// accuracy and correct (roll back) the interpolators.
// This operation will also clip the beginning of the span
// if necessary.
//-------------------------
int start = pc1->m_x - (x << subpixel_shift);
v -= start;
a -= start;
nlen += start;
int vv, va;
enum lim_e { lim = color_type::base_mask };
// Beginning part of the span. Since we rolled back the
// interpolators, the color values may have overflow.
// So that, we render the beginning part with checking
// for overflow. It lasts until "start" is positive;
// typically it's 1-2 pixels, but may be more in some cases.
//-------------------------
while(len && start > 0)
{
vv = v.y();
va = a.y();
if(vv < 0) vv = 0; if(vv > lim) vv = lim;
if(va < 0) va = 0; if(va > lim) va = lim;
span->v = (value_type)vv;
span->a = (value_type)va;
v += subpixel_scale;
a += subpixel_scale;
nlen -= subpixel_scale;
start -= subpixel_scale;
++span;
--len;
}
// Middle part, no checking for overflow.
// Actual spans can be longer than the calculated length
// because of anti-aliasing, thus, the interpolators can
// overflow. But while "nlen" is positive we are safe.
//-------------------------
while(len && nlen > 0)
{
span->v = (value_type)v.y();
span->a = (value_type)a.y();
v += subpixel_scale;
a += subpixel_scale;
nlen -= subpixel_scale;
++span;
--len;
}
// Ending part; checking for overflow.
// Typically it's 1-2 pixels, but may be more in some cases.
//-------------------------
while(len)
{
vv = v.y();
va = a.y();
if(vv < 0) vv = 0; if(vv > lim) vv = lim;
if(va < 0) va = 0; if(va > lim) va = lim;
span->v = (value_type)vv;
span->a = (value_type)va;
v += subpixel_scale;
a += subpixel_scale;
++span;
--len;
}
}
private:
bool m_swap;
int m_y2;
gray_calc m_c1;
gray_calc m_c2;
gray_calc m_c3;
};
}
#endif
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