genode/repos/gems/include/polygon_gfx/clipping.h

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/*
* \brief Polygon clipping
* \date 2015-06-19
* \author Norman Feske
*/
/*
* Copyright (C) 2015-2017 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU Affero General Public License version 3.
*/
#ifndef _INCLUDE__POLYGON_GFX__CLIPPING_H_
#define _INCLUDE__POLYGON_GFX__CLIPPING_H_
namespace Polygon {
struct Point_base;
inline int intersect_ratio(int, int, int);
template <typename> struct Clipper_vertical;
template <typename> struct Clipper_horizontal;
struct Clipper_min;
struct Clipper_max;
template <typename, typename, typename> struct Clipper;
template <typename> struct Clipper_2d;
}
/**
* Common base class of polygon points
*/
struct Polygon::Point_base : Genode::Point<>
{
/*
* Number of attributes to interpolate along the polygon edges. This value
* must be defined by each derived class.
*/
enum { NUM_EDGE_ATTRIBUTES = 1 };
/**
* Constructors
*/
Point_base() { }
Point_base(int x, int y): Genode::Point<>(x, y) { }
/**
* Return edge attribute by ID
*/
inline int edge_attr(int) const { return x(); }
/**
* Assign value to edge attribute with specified ID
*/
inline void edge_attr(int, int value) { *this = Point_base(value, y()); }
};
/**
* Calculate ratio of range intersection
*
* \param v_start Start of range
* \param v_end End of range
* \param v_cut Range cut (should be in interval v_start...v_end)
* \return Ratio of intersection as 16.16 fixpoint
*
* The input arguments 'v_start', 'v_end', 'v_cut' must use only
* the lower 16 bits of the int type.
*/
inline int Polygon::intersect_ratio(int v_start, int v_end, int v_cut)
{
int dv = v_end - v_start,
dv_cut = v_cut - v_start;
return dv ? (dv_cut<<16)/dv : 0;
}
/**
* Support for vertical clipping boundary
*/
template <typename POINT>
struct Polygon::Clipper_vertical
{
/**
* Select clipping-sensitive attribute from polygon point
*/
static int clip_value(POINT p) { return p.x(); }
/**
* Calculate intersection point
*/
static POINT clip(POINT p1, POINT p2, int clip)
{
/*
* Enforce unique x order of points to apply rounding errors
* consistently also when edge points are specified in reverse.
* Typically the same edge is used in reverse direction by
* each neighboured polygon.
*/
if (clip_value(p1) > clip_value(p2)) { POINT tmp = p1; p1 = p2; p2 = tmp; }
/* calculate ratio of the intersection of edge and clipping boundary */
int ratio = intersect_ratio(p1.x(), p2.x(), clip);
/* calculate y value at intersection point */
POINT result;
*(Point_base *)&result = Point_base(clip, p1.y() + ((ratio*(p2.y() - p1.y()))>>16));
/* calculate intersection values for edge attributes other than x */
for (int i = 1; i < POINT::NUM_EDGE_ATTRIBUTES; i++) {
int v1 = p1.edge_attr(i),
v2 = p2.edge_attr(i);
result.edge_attr(i, v1 + ((ratio*(v2 - v1))>>16));
}
return result;
}
};
/**
* Support for horizontal clipping boundary
*/
template <typename POINT>
struct Polygon::Clipper_horizontal
{
/**
* Select clipping-sensitive attribute from polygon point
*/
static int clip_value(POINT p) { return p.y(); }
/**
* Calculate intersection point
*/
static POINT clip(POINT p1, POINT p2, int clip)
{
if (clip_value(p1) > clip_value(p2)) { POINT tmp = p1; p1 = p2; p2 = tmp; }
/* calculate ratio of the intersection of edge and clipping boundary */
int ratio = intersect_ratio(clip_value(p1), clip_value(p2), clip);
/* calculate y value at intersection point */
POINT result;
*(Point_base *)&result = Point_base(p1.x() + ((ratio*(p2.x() - p1.x()))>>16), clip);
/* calculate intersection values for edge attributes other than x */
for (int i = 1; i < POINT::NUM_EDGE_ATTRIBUTES; i++) {
int v1 = p1.edge_attr(i),
v2 = p2.edge_attr(i);
result.edge_attr(i, v1 + ((ratio*(v2 - v1))>>16));
}
return result;
}
};
/**
* Support for clipping against a lower boundary
*/
struct Polygon::Clipper_min
{
static bool inside(int value, int boundary) { return value >= boundary; }
};
/**
* Support for clipping against a higher boundary
*/
struct Polygon::Clipper_max
{
static bool inside(int value, int boundary) { return value <= boundary; }
};
/**
* One-dimensional clipping
*
* This template allows for the aggregation of the policies defined above to
* build specialized 1D-clipping functions for upper/lower vertical/horizontal
* clipping boundaries and for polygon points with different attributes.
*/
template <typename CLIPPER_DIRECTION, typename CLIPPER_MINMAX, typename POINT>
struct Polygon::Clipper : CLIPPER_DIRECTION, CLIPPER_MINMAX
{
/**
* Check whether point is inside the clipping area or not
*/
static bool inside(POINT p, int clip)
{
return CLIPPER_MINMAX::inside(CLIPPER_DIRECTION::clip_value(p), clip);
}
};
/**
* Create clipping helpers
*
* This class is used as a compound containing all rules to
* clip a polygon against a 2d region such as the clipping
* region of a Canvas.
*/
template <typename POINT>
struct Polygon::Clipper_2d
{
typedef Clipper<Clipper_horizontal<POINT>, Clipper_min, POINT> Top;
typedef Clipper<Clipper_horizontal<POINT>, Clipper_max, POINT> Bottom;
typedef Clipper<Clipper_vertical<POINT>, Clipper_min, POINT> Left;
typedef Clipper<Clipper_vertical<POINT>, Clipper_max, POINT> Right;
};
#endif /* _INCLUDE__POLYGON_GFX__CLIPPING_H_ */