degenerate_policy.h

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/** @file
 *  @author Bram de Greve (bramz@users.sourceforge.net)
 *  @author Tom De Muer (tomdemuer@users.sourceforge.net)
 *
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 *  the License. You may obtain a copy of the License at 
 *  http://lass.sourceforge.net/cpal-license. The License is based on the 
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 *  with Exhibit B.
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 *  The Original Code is LASS - Library of Assembled Shared Sources.
 *  
 *  The Initial Developer of the Original Code is Bram de Greve and Tom De Muer.
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 *  *** END LICENSE INFORMATION ***
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/** @defgroup DegeneratePolicy DegeneratePolicy
 *  @brief policies to specify the rules for degenerate polygons and others..
 *  @author Bram de Greve
 *  @date 2003
 *
 *  Polygons and triangles can be degenerate.  e.g. when they have less than
 *  3 vertices, or some vertices are coincident, or colinear.  We provide a few
 *  policies to deal with this.
 */

#ifndef LASS_GUARDIAN_OF_INCLUSION_PRIM_DEGENERATE_POLICY_H
#define LASS_GUARDIAN_OF_INCLUSION_PRIM_DEGENERATE_POLICY_H


#include "prim_common.h"
#include "../util/enforcer.h"

namespace lass
{
namespace prim
{

/** @ingroup DegeneratePolicy
 */
class DegenerationError: public util::Exception
{
public:
    DegenerationError(const std::string& msg, const std::string& loc): util::Exception(msg, loc) {}
private:
    LASS_UTIL_EXCEPTION_PRIVATE_IMPL(DegenerationError)
};



/** @ingroup DegeneratePolicy
 *
 *  This is the default policy
 *
 *  NoDegenerate will not prevent a primitive to become degenerate, but it will check some
 *  basic conditions when you try to do "unsafe" operations and throws
 *  an exception on failure.  e.g. CheckDegenerate will not allow you to get the @c edge(0)
 *  or @c vector(0) of a polygon with only one vertex.
 *
 *  However, it will not check all posible conditions.  It will avoid expensive predicates.
 *  e.g. it will avoid to test if a polygon is simple, because that's too expensive.  If you
 *  want all conditions to be checked, you should use StrictNoDegenerate
 */
struct NoDegenerate
{
    template <class Primitive>
    static void enforceEdge(const Primitive& iPrimitive, int iIndexOfTailVertex)
    {
        if (iPrimitive.at(iIndexOfTailVertex) == iPrimitive.at(iIndexOfTailVertex + 1))
        {
            LASS_THROW_EX(DegenerationError, "Degenerate edge detected at tail vertex '" << iIndexOfTailVertex << "'.");
        }
    }

    template <class Primitive>
    static void enforceSimple(const Primitive& /*iPrimitive*/)
    {
    }

    template <class Primitive>
    static const typename Primitive::TValue enforceNonZeroSignedArea(const Primitive& iPrimitive)
    {
        const typename Primitive::TValue result = iPrimitive.signedArea();
        if (result == Primitive::TNumTraits::zero)
        {
            LASS_THROW_EX(DegenerationError, "Area of primitive is zero.");
        }
        return result;
    }
};



/** @ingroup DegeneratePolicy
 *
 *  This is the default policy
 *
 *  StrictNoDegenerate is similar to NoDegenerate, but will check more conditions.  However, this
 *  might go wild on cpu usage (read: be very slow).  Use this if you really need to be on the safe
 *  side.
 */
struct StrictNoDegenerate
{
    template <class Primitive>
    static void enforceEdge(const Primitive& iPrimitive, int iIndexOfTailVertex)
    {
        if (iPrimitive.at(iIndexOfTailVertex) == iPrimitive.at(iIndexOfTailVertex + 1))
        {
            LASS_THROW_EX(DegenerationError, "Degenerate edge detected at tail vertex '" << iIndexOfTailVertex << "'.");
        }
    }

    template <class Primitive>
    static void enforceSimple(const Primitive& iPrimitive)
    {
        if (!iPrimitive.isSimple())
        {
            LASS_THROW_EX(DegenerationError, "polygon is not simple.");
        }
    }

    template <class Primitive>
    static const typename Primitive::TValue enforceNonZeroSignedArea(const Primitive& iPrimitive)
    {
        const typename Primitive::TValue result = iPrimitive.signedArea();
        if (result == Primitive::TNumTraits::zero)
        {
            LASS_THROW_EX(DegenerationError, "Area of primitive is zero.");
        }
        return result;
    }
};



/** @ingroup DegeneratePolicy
 *
 *  AllowDegenerate puts the responsibility on the user.  It will assume all conditions are fullfilled
 *  and continue like nothing is wrong.  This is the "best guess" thing.
 */
struct AllowDegenerate
{
    template <class Primitive>
    static void enforceEdge(const Primitive& /*iPrimitive*/, int /*iIndexOfTailVertex*/)
    {
    }

    template <class Primitive>
    static void enforceSimple(const Primitive& /*iPrimitive*/)
    {
    }

    template <class Primitive>
    static const typename Primitive::TValue enforceNonZeroSignedArea(const Primitive& iPrimitive)
    {
        return iPrimitive.signedArea();
    }
};


}

}

// --- implementation ------------------------------------------------------------------------------

namespace lass
{
namespace prim
{
namespace impl
{

/** raises exception in case primitive is degenerate and we have restricting
 *  @relates lass::prim::Bounded
 */
/*
struct DegenerateRaiser
{
    template <class T>
    static void raise(const T&, const std::string& iMessage, const char* iLocus)
    {
        LASS_THROW_EX(DegenerationError, iMessage << '\n' << iLocus);
    }
};
*/

}

}

}



#endif

// EOF