linelistlabel.cpp

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/***************************************************************************
                    linelistlabel.cpp -  K Desktop Planetarium
                             -------------------
    begin               : 2007-08-08
    copyright           : (C) 2007 James B. Bowlin
    email               : bowlin@mindspring.com
 ***************************************************************************/

/***************************************************************************
 *                                                                       *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or   *
 *   (at your option) any later version.                                   *
 *                                                                       *
 ***************************************************************************/

#include <QString>

#include "linelistlabel.h"
#include "Options.h"
#include "skyobjects/skypoint.h"
#include "skymap.h"
#include "skylabeler.h"
#include "linelist.h"
#include "projections/projector.h"

LineListLabel::LineListLabel( const QString& text )
        : m_text( text )
{
    m_skyLabeler = SkyLabeler::Instance();

    // prevent a crash if drawGuideLabel() is called before reset()
    for ( int i = 0; i < 4; i++ ) {
        m_labList[i] = 0;
        m_labIndex[i] = 0;
    }
}

void LineListLabel::reset()
{
    // These are the indices of the farthest left point, farthest right point,
    // etc.  The are data members so the drawLabels() routine can use them.
    // Zero indicates an index that was never set and is considered invalid
    // inside of drawLabels().
    for ( int i = 0; i < 4; i++ ) {
        m_labList[i] = 0;
        m_labIndex[i] = 0;
    }

    // These are used to keep track of the element that is farthest left,
    // farthest right, etc.
    m_farLeft  = 100000.0;
    m_farRight = 0.0;
    m_farTop   = 100000.0;
    m_farBot   = 0.0;

    m_skyLabeler->getMargins( m_text, &m_marginLeft, &m_marginRight,
                              &m_marginTop, &m_marginBot );
}

void LineListLabel::updateLabelCandidates( qreal x, qreal y, LineList* lineList, int i )
{
    if ( i < 1 ) return;

    if ( x < m_marginLeft || x > m_marginRight ||
            y < m_marginTop  || y > m_marginBot ) return;

    if ( x < m_farLeft ) {
        m_labIndex[LeftCandidate] = i;
        m_labList[LeftCandidate]  = lineList;
        m_farLeft = x;
    }
    if ( x > m_farRight ) {
        m_labIndex[RightCandidate] = i;
        m_labList[RightCandidate]  = lineList;
        m_farRight = x;
    }
    if (  y > m_farBot ) {
        m_labIndex[BotCandidate] = i;
        m_labList[BotCandidate]  = lineList;
        m_farBot = x;
    }
    if ( y < m_farTop ) {
        m_labIndex[TopCandidate] = i;
        m_labList[TopCandidate]  = lineList;
        m_farTop = x;
    }
}


void LineListLabel::draw()
{
    const Projector *proj = SkyMap::Instance()->projector();

    double comfyAngle = 40.0;  // the first valid candidate with an angle
    // smaller than this gets displayed.  If you set
    // this to > 90. then the first valid candidate
    // will be displayed, regardless of angle.

    // We store info about the four candidate points in arrays to make several
    // of the steps easier, particularly choosing the valid candidate with the
    // smallest angle from the horizontal.

    int       idx[4];                                 // index of candidate
    LineList* list[4];                                // LineList of candidate
    double    a[4] = { 360.0, 360.0, 360.0, 360.0 };  // angle, default to large value
    QPointF   o[4];                                   // candidate point
    bool      okay[4] = { true, true, true, true };   // flag  candidate false if it
    // overlaps a previous label.

    // We no longer adjust the order but if we were to it would be here
    static int Order[4]  =
        { LeftCandidate, BotCandidate, TopCandidate, LeftCandidate };

    for ( int j = 0; j < 4; j++ ) {
        idx[j]  = m_labIndex[ Order[ j ] ];
        list[j] = m_labList[  Order[ j ] ];
    }

    // Make sure start with a valid candidate
    int first = 0;
    for ( ; first < 4; first++ ) {
        if ( idx[first] ) break;
    }

    // return if there are no valid candidates
    if ( first >= 4 ) return;


    // Try the points in order and print the label if we can draw it at
    // a comfortable angle for viewing;
    for ( int j = first; j < 4; j++ ) {
        o[j] = angleAt( proj, list[j], idx[j], &a[j] );

        if ( ! idx[j] || ! proj->checkVisibility( list[j]->at( idx[j] ) ) ) {
            okay[j] = false;
            continue;
        }

        if ( fabs( a[j] ) > comfyAngle )
            continue;

        if ( m_skyLabeler->drawGuideLabel( o[j], m_text, a[j] ) )
            return;

        okay[j] = false;
    }

    //--- No angle was comfy so pick the one with the smallest angle ---

    // Index of the index/angle/point that gets displayed
    int best = first;

    // find first valid candidate that does not overlap existing labels
    for ( ; best < 4; best++ ) {
        if ( idx[best] && okay[best] ) break;
    }

    // return if all candiates either overlap or are invalid
    if ( best >= 4 ) return;

    // find the valid non-overlap candidate with the smallest angle
    for ( int j = best + 1; j < 4; j++ ) {
        if ( idx[j] && okay[j] && fabs(a[j]) < fabs(a[best]) ) best = j;
    }

    m_skyLabeler->drawGuideLabel( o[best], m_text, a[best] );
}


QPointF LineListLabel::angleAt( const Projector *proj, LineList* list, int i, double *angle )
{
    SkyPoint* pThis = list->at( i );
    SkyPoint* pLast = list->at( i - 1 );

    QPointF oThis = proj->toScreen( pThis );
    QPointF oLast = proj->toScreen( pLast );

    double sx = double( oThis.x() - oLast.x() );
    double sy = double( oThis.y() - oLast.y() );

    *angle = atan2( sy, sx ) * 180.0 / dms::PI;

    // FIXME: use clamp in KSUtils
    // Never draw the label upside down
    if ( *angle < -90.0 ) *angle += 180.0;
    if ( *angle >  90.0 ) *angle -= 180.0;

    return oThis;
}