1 files changed, 113 insertions, 0 deletions
diff --git a/basegfx/source/tools/zoomtools.cxx b/basegfx/source/tools/zoomtools.cxx
new file mode 100644
index 000000000..488b19b31
--- /dev/null
+++ b/basegfx/source/tools/zoomtools.cxx
@@ -0,0 +1,113 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <basegfx/utils/zoomtools.hxx>
+
+namespace basegfx::zoomtools
+{
+
+/** 2^(1/6) as the default step
+
+    This ensures (unless the rounding is used) that 6 steps lead
+    to double / half zoom level.
+*/
+const double ZOOM_FACTOR = 1.12246205;
+
+/**
+* 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 some values are not skipped
+    nNew = enforceStep(nNew, nCurrent, 200);
+    nNew = enforceStep(nNew, nCurrent, 100);
+    nNew = enforceStep(nNew, nCurrent, 75);
+    nNew = enforceStep(nNew, nCurrent, 50);
+    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 some values are not skipped
+    nNew = enforceStep(nNew, nCurrent, 200);
+    nNew = enforceStep(nNew, nCurrent, 100);
+    nNew = enforceStep(nNew, nCurrent, 75);
+    nNew = enforceStep(nNew, nCurrent, 50);
+    nNew = enforceStep(nNew, nCurrent, 25);
+    return nNew;
+}
+} // namespace
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */