optimized zoom to use more common intervals

Round zoom values beginning with 50 to a multiple of 5, with 100 to one
of 10, with 500 to one of 50 and with 1000 to one of 100.
The step 100 is enforced to have one fixed point.

1 files changed, 150 insertions, 0 deletions

diff --git a/basegfx/source/tools/zoomtools.cxx b/basegfx/source/tools/zoomtools.cxx
new file mode 100644
index 000000000000..c6c8044c5953
--- /dev/null
+++ b/basegfx/source/tools/zoomtools.cxx
@@ -0,0 +1,150 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * Version: MPL 1.1 / GPLv3+ / LGPLv3+
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License or as specified alternatively below. You may obtain a copy of
+ * the License at http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * Major Contributor(s):
+ * Copyright (C) 2012 Tim Hardeck <thardeck@suse.com>
+ *
+ * All Rights Reserved.
+ *
+ * For minor contributions see the git repository.
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 3 or later (the "GPLv3+"), or
+ * the GNU Lesser General Public License Version 3 or later (the "LGPLv3+"),
+ * in which case the provisions of the GPLv3+ or the LGPLv3+ are applicable
+ * instead of those above.
+ */
+
+#include <basegfx/tools/zoomtools.hxx>
+
+namespace basegfx
+{
+namespace zoomtools
+{
+
+/** 2^(1/4) as the default step
+
+    This ensures (unless the rounding is used) that 4 steps lead
+    to double / half zoom level.
+*/
+const double ZOOM_FACTOR = 1.1892071150027210667175;
+
+/**
+* Round a value against a specified multiple. Values below half
+* of the multiple are rounded down and all others are rounded up.
+*
+* @param nCurrent current value
+* @param nMultiple multiple against which the current value is rounded
+*/
+static long roundMultiple(long nCurrent, int nMultiple)
+{
+    // round zoom to a multiple of nMultiple
+    return (( nCurrent + nMultiple / 2 ) - ( nCurrent + nMultiple / 2 ) % nMultiple);
+}
+
+/**
+* Convert geometric progression results into more common values by
+* rounding them against certain multiples depending on the size.
+* Beginning with 50 the multiple is 5, with 100, 10, and so on.
+*
+* @param nCurrent current zoom factor
+*/
+static long roundZoom(double nCurrent)
+{
+    // convert nCurrent properly to int
+    long nNew = nCurrent + 0.5;
+
+    // round to more common numbers above 50
+    if (nNew > 1000) {
+        nNew = roundMultiple(nNew, 100);
+    } else if ( nNew > 500 ) {
+        nNew = roundMultiple(nNew, 50);
+    } else if ( nNew > 100 ) {
+        nNew = roundMultiple(nNew, 10);
+    } else if ( nNew > 50 ) {
+        nNew = roundMultiple(nNew, 5);
+    }
+
+    return nNew;
+}
+
+/**
+* Make sure that a certain step isn't skipped during the zooming
+* progress.
+*
+* @param nCurrent current zoom factor
+* @param nPrevious previous zoom factor
+* @param nStep step which shouldn't be skipped
+*/
+static long enforceStep(long nCurrent, long nPrevious, int nStep)
+{
+    if ((( nCurrent > nStep ) && ( nPrevious < nStep ))
+    || (( nCurrent < nStep ) && ( nPrevious > nStep )))
+        return nStep;
+    else
+        return nCurrent;
+}
+
+/**
+* Increasing the zoom level.
+*
+* @param nCurrent current zoom factor
+*/
+long zoomIn(long nCurrent)
+{
+    long nNew = roundZoom( nCurrent * ZOOM_FACTOR );
+    // make sure 100% isn't skipped
+    nNew = enforceStep(nNew, nCurrent, 100);
+    nNew = enforceStep(nNew, nCurrent, 25);
+    return nNew;
+}
+
+/**
+* Decreasing the zoom level.
+*
+* @param nCurrent current zoom factor
+*/
+long zoomOut(long nCurrent)
+{
+    long nNew = roundZoom( nCurrent / ZOOM_FACTOR );
+    // make sure 100% isn't skipped
+    nNew = enforceStep(nNew, nCurrent, 100);
+    nNew = enforceStep(nNew, nCurrent, 25);
+    return nNew;
+}
+
+/**
+* Increasing the zoom level.
+*
+* @param nCurrent current zoom factor
+*/
+int zoomIn(int nCurrent)
+{
+    return static_cast<int>( zoomIn( long( nCurrent ) ) );
+}
+
+/**
+* Decreasing the zoom level.
+*
+* @param nCurrent current zoom factor
+*/
+int zoomOut(int nCurrent)
+{
+    return static_cast<int>( zoomOut( long( nCurrent ) ) );
+}
+
+} // namespace zoomtools
+} // namespace basegfx
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */