Update change-log and documentation regarding improved HighDPI support

Author: ptziegler

CHANGELOG.md

@@ -7,7 +7,11 @@
 
 ## Zest
 
+## General
 
+- Experimental: The native HighDPI scaling provided by SWT can be replaced with a Draw2D-based scaling may by setting
+                the `*draw2d.enableAutoscale*` to `*true*`. Doing so avoids visual artifacts that result from
+                fractional scaling. This property is only available on Windows and enabled by default.
 
 # GEF Classic 3.25.0
 

org.eclipse.gef.doc.isv/guide-src/guide.adoc

@@ -20,6 +20,7 @@ endif::[]
 * xref:#tools-and-the-palette[Tools and Palette]
 * xref:#types-of-interactions-in-gef[Interactions] - the GEF interactions and
   the players involved
+* xref:#highdpi-support[HighDPI Support]
 
 === [#overview]#Overview#
 
@@ -1068,4 +1069,21 @@ connection to avoid figures. The handles for creating and moving
 bendpoints are labeled with the index that the BendpointRequest will
 contain. The index is the same as the current (or eventual) index of the
 bendpoint in the routing constraint's List.
-|===
+|===
+
+=== [#highdpi-support]#HighDPI Support#
+
+The `*Figures*` used for visualization of the `*EditParts*` are painted using absolute coordinates. When used in
+combination with fractional scaling, the resulting rounding errors may cause glitches and other visual artifacts in the
+editor. GEF provides an experimental mode, where the scaling is not done by SWT, but rather by Draw2D. 
+
+By setting the `*draw2d.enableAutoscale*` system property, the native auto-scaling functionality of the `*Canvas*`,
+which is normally provided by SWT, is replaced by a Draw2D-based scaling. A `*ZoomChanged*` is hooked to the 
+`*EditPartViewer*`, listening to changes to the `*monitorScale*` of the underlying `*Control*` and setting the current
+zoom as property of the viewer. The `*RootEditPart*` listens to changes of this property and updates the scale of its 
+`*ScalableFigure*`.
+
+image:images/highdpi.svg[Relation between the FigureCanvas, EditPartViewer and RootEditPart with respect to the device zoom]
+
+image:images/important.gif[image] Fractional scaling is currently only supported for Windows, where this system property
+is enabled by default. On Linux and MacOS, this system property is ignored.