basegfx/source/tools/zoomtools.cxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  */
   9
  10 #include <basegfx/tools/zoomtools.hxx>
  11
  12 namespace basegfx
  13 {
  14 namespace zoomtools
  15 {
  16
  17 /** 2^(1/6) as the default step
  18
  19     This ensures (unless the rounding is used) that 6 steps lead
  20     to double / half zoom level.
  21 */
  22 const double ZOOM_FACTOR = 1.12246205;
  23
  24 /**
  25 * Round a value against a specified multiple. Values below half
  26 * of the multiple are rounded down and all others are rounded up.
  27 *
  28 * @param nCurrent current value
  29 * @param nMultiple multiple against which the current value is rounded
  30 */
  31 static long roundMultiple(long nCurrent, int nMultiple)
  32 {
  33     // round zoom to a multiple of nMultiple
  34     return (( nCurrent + nMultiple / 2 ) - ( nCurrent + nMultiple / 2 ) % nMultiple);
  35 }
  36
  37 /**
  38 * Convert geometric progression results into more common values by
  39 * rounding them against certain multiples depending on the size.
  40 * Beginning with 50 the multiple is 5, with 100, 10, and so on.
  41 *
  42 * @param nCurrent current zoom factor
  43 */
  44 static long roundZoom(double nCurrent)
  45 {
  46     // convert nCurrent properly to int
  47     long nNew = nCurrent + 0.5;
  48
  49     // round to more common numbers above 50
  50     if (nNew > 1000) {
  51         nNew = roundMultiple(nNew, 100);
  52     } else if ( nNew > 500 ) {
  53         nNew = roundMultiple(nNew, 50);
  54     } else if ( nNew > 100 ) {
  55         nNew = roundMultiple(nNew, 10);
  56     } else if ( nNew > 50 ) {
  57         nNew = roundMultiple(nNew, 5);
  58     }
  59
  60     return nNew;
  61 }
  62
  63 /**
  64 * Make sure that a certain step isn't skipped during the zooming
  65 * progress.
  66 *
  67 * @param nCurrent current zoom factor
  68 * @param nPrevious previous zoom factor
  69 * @param nStep step which shouldn't be skipped
  70 */
  71 static long enforceStep(long nCurrent, long nPrevious, int nStep)
  72 {
  73     if ((( nCurrent > nStep ) && ( nPrevious < nStep ))
  74     || (( nCurrent < nStep ) && ( nPrevious > nStep )))
  75         return nStep;
  76     else
  77         return nCurrent;
  78 }
  79
  80 /**
  81 * Increasing the zoom level.
  82 *
  83 * @param nCurrent current zoom factor
  84 */
  85 long zoomIn(long nCurrent)
  86 {
  87     long nNew = roundZoom( nCurrent * ZOOM_FACTOR );
  88     // make sure some values are not skipped
  89     nNew = enforceStep(nNew, nCurrent, 200);
  90     nNew = enforceStep(nNew, nCurrent, 100);
  91     nNew = enforceStep(nNew, nCurrent, 75);
  92     nNew = enforceStep(nNew, nCurrent, 50);
  93     nNew = enforceStep(nNew, nCurrent, 25);
  94     return nNew;
  95 }
  96
  97 /**
  98 * Decreasing the zoom level.
  99 *
 100 * @param nCurrent current zoom factor
 101 */
 102 long zoomOut(long nCurrent)
 103 {
 104     long nNew = roundZoom( nCurrent / ZOOM_FACTOR );
 105     // make sure some values are not skipped
 106     nNew = enforceStep(nNew, nCurrent, 200);
 107     nNew = enforceStep(nNew, nCurrent, 100);
 108     nNew = enforceStep(nNew, nCurrent, 75);
 109     nNew = enforceStep(nNew, nCurrent, 50);
 110     nNew = enforceStep(nNew, nCurrent, 25);
 111     return nNew;
 112 }
 113 } // namespace zoomtools
 114 } // namespace basegfx
 115
 116 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */