SunLightBlending.cpp

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// Copyright 2010 Jens-Michael Hoffmann <jmho@c-xx.com>
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library 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
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library. If not, see <http://www.gnu.org/licenses/>.

#include "SunLightBlending.h"

#include "MarbleDebug.h"
#include "SunLocator.h"
#include "TextureTile.h"
#include "TileLoaderHelper.h"
#include "MarbleGlobal.h"

#include <QImage>

#include <cmath>

namespace Marble
{

SunLightBlending::SunLightBlending( const SunLocator * sunLocator )
    : Blending(),
      m_sunLocator( sunLocator ),
      m_levelZeroColumns( 0 ),
      m_levelZeroRows( 0 )
{
}

SunLightBlending::~SunLightBlending()
{
}

void SunLightBlending::blend( QImage * const tileImage, TextureTile const * const top ) const
{
    if ( tileImage->depth() != 32 )
        return;

    // TODO add support for 8-bit maps?
    // add sun shading
    const TileId id = top->id();
    const qreal  global_width  = tileImage->width()
        * TileLoaderHelper::levelToColumn( m_levelZeroColumns, id.zoomLevel() );
    const qreal  global_height = tileImage->height()
        * TileLoaderHelper::levelToRow( m_levelZeroRows, id.zoomLevel() );
    const qreal lon_scale = 2*M_PI / global_width;
    const qreal lat_scale = -M_PI / global_height;
    const int tileHeight = tileImage->height();
    const int tileWidth = tileImage->width();

    // First we determine the supporting point interval for the interpolation.
    const int n = maxDivisor( 30, tileWidth );
    const int ipRight = n * (int)( tileWidth / n );

    const QImage *nighttile = top->image();

    for ( int cur_y = 0; cur_y < tileHeight; ++cur_y ) {
        const qreal lat = lat_scale * ( id.y() * tileHeight + cur_y ) - 0.5*M_PI;
        const qreal a = sin( ( lat+DEG2RAD * m_sunLocator->getLat() )/2.0 );
        const qreal c = cos(lat)*cos( -DEG2RAD * m_sunLocator->getLat() );

        QRgb* scanline  = (QRgb*)tileImage->scanLine( cur_y );
        const QRgb* nscanline = (QRgb*)nighttile->scanLine( cur_y );

        qreal lastShade = -10.0;

        int cur_x = 0;

        while ( cur_x < tileWidth ) {

            const bool interpolate = ( cur_x != 0 && cur_x < ipRight && cur_x + n < tileWidth );

            qreal shade = 0;

            if ( interpolate ) {
                const int check = cur_x + n;
                const qreal checklon   = lon_scale * ( id.x() * tileWidth + check );
                shade = m_sunLocator->shading( checklon, a, c );

                // if the shading didn't change across the interpolation
                // interval move on and don't change anything.
                if ( shade == lastShade && shade == 1.0 ) {
                    scanline += n;
                    nscanline += n;
                    cur_x += n;
                    continue;
                }
                if ( shade == lastShade && shade == 0.0 ) {
                    for ( int t = 0; t < n; ++t ) {
                        m_sunLocator->shadePixelComposite( *scanline, *nscanline, shade );
                        ++scanline;
                        ++nscanline;
                    }
                    cur_x += n;
                    continue;
                }
                for ( int t = 0; t < n ; ++t ) {
                    qreal lon   = lon_scale * ( id.x() * tileWidth + cur_x );
                    shade = m_sunLocator->shading( lon, a, c );
                    m_sunLocator->shadePixelComposite( *scanline, *nscanline, shade );
                    ++scanline;
                    ++nscanline;
                    ++cur_x;
                }
            }

            else {
                // Make sure we don't exceed the image memory
                if ( cur_x < tileWidth ) {
                    qreal lon   = lon_scale * ( id.x() * tileWidth + cur_x );
                    shade = m_sunLocator->shading( lon, a, c );
                    m_sunLocator->shadePixelComposite( *scanline, *nscanline, shade );
                    ++scanline;
                    ++nscanline;
                    ++cur_x;
                }
            }
            lastShade = shade;
        }
    }
}

void SunLightBlending::setLevelZeroLayout( int levelZeroColumns, int levelZeroRows )
{
    m_levelZeroColumns = levelZeroColumns;
    m_levelZeroRows = levelZeroRows;
}

// TODO: This should likely go into a math class in the future ...
int SunLightBlending::maxDivisor( int maximum, int fullLength )
{
    // Find the optimal interpolation interval n for the
    // current image canvas width
    int best = 2;

    int nEvalMin = fullLength;
    for ( int it = 1; it <= maximum; ++it ) {
        // The optimum is the interval which results in the least amount
        // supporting points taking into account the rest which can't
        // get used for interpolation.
        int nEval = fullLength / it + fullLength % it;
        if ( nEval < nEvalMin ) {
            nEvalMin = nEval;
            best = it;
        }
    }
    return best;
}

}