keystoplerp.cxx

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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#include <basegfx/utils/keystoplerp.hxx>
#include <com/sun/star/uno/Sequence.hxx>
#include <osl/diagnose.h>
 
#include <algorithm>
 
static void validateInput(const std::vector<double>& rKeyStops)
{
#ifdef DBG_UTIL
    OSL_ENSURE( rKeyStops.size() > 1,
                "KeyStopLerp::KeyStopLerp(): key stop vector must have two entries or more" );
 
    // rKeyStops must be sorted in ascending order
    for( std::size_t i=1, len=rKeyStops.size(); i<len; ++i )
    {
        if( rKeyStops[i-1] > rKeyStops[i] )
            OSL_FAIL( "KeyStopLerp::KeyStopLerp(): time vector is not sorted in ascending order!" );
    }
#else
    (void)rKeyStops;
#endif
}
 
namespace basegfx::utils
{
        KeyStopLerp::KeyStopLerp( std::vector<double>&& rKeyStops ) :
            maKeyStops(std::move(rKeyStops)),
            mnLastIndex(0)
        {
            validateInput(maKeyStops);
        }
 
        KeyStopLerp::KeyStopLerp( const ::css::uno::Sequence<double>& rKeyStops ) :
            maKeyStops(rKeyStops.begin(), rKeyStops.end()),
            mnLastIndex(0)
        {
            validateInput(maKeyStops);
        }
 
        KeyStopLerp::ResultType KeyStopLerp::lerp(double fAlpha) const
        {
            // cached value still okay?
            if( maKeyStops.at(mnLastIndex) < fAlpha ||
                maKeyStops.at(mnLastIndex+1) >= fAlpha )
            {
                // nope, find new index
                mnLastIndex = std::min<std::ptrdiff_t>(
                    maKeyStops.size()-2,
                    // range is ensured by max below
                    std::max<std::ptrdiff_t>(
                        0,
                        std::distance( maKeyStops.begin(),
                                       std::lower_bound( maKeyStops.begin(),
                                                         maKeyStops.end(),
                                                         fAlpha )) - 1 ));
            }
 
            // lerp between stop and stop+1
            const double fRawLerp=
                (fAlpha-maKeyStops.at(mnLastIndex)) /
                (maKeyStops.at(mnLastIndex+1) - maKeyStops.at(mnLastIndex));
 
            // clamp to permissible range (input fAlpha might be
            // everything)
            return ResultType(
                mnLastIndex,
                std::clamp(fRawLerp,0.0,1.0));
        }
}
 
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