[Lazarus] Calling DrawFocusRect() outside the Paint() event
nc-gaertnma at netcologne.de
Mon Oct 10 11:49:32 CEST 2016
On Mon, 10 Oct 2016 10:21:48 +0100
Graeme Geldenhuys via Lazarus <lazarus at lists.lazarus-ide.org> wrote:
> Working on a visual report designer for the upcoming fpReport. We use
> Canvas.DrawFocusRect() to draw a selection rectangle around a reporting
> element (eg: a memo). We can drag that rectangle around in the report
> designer (which itself is a custom widget). We call the
> Canvas.DrawFocusRect() from within the MouseMove event. It seems to work
> fine under LCL-GTK2, but could this be problematic on other platforms,
> as painting outside the Paint event can normally have undefined results.
Some widgetsets like Carbon can only paint during the Paint event.
> Or has LCL somehow resolved the issues of painting outside the Paint event?
If you want to optimize for mini changes like the focusrect you might
want to use a bitmap.
> On a side note:
> The Paint() event for the report designer can potentially have very
> lengthy code, so we definitely don't want to repaint everything simply
> because we are dragging a focus rectangle around on the canvas. So if we
> must, we can obviously work around this by using various states in the
> Paint method.
You need to optimize the Paint event anyway.
You don't need to draw everything when using InvalidateRect instead
And in Paint use Canvas.GetClipRect or lclintf's GetClipRGN to avoid
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