Re: [OpenMap Users] How can I effectively use repaint()?

From: Don Dietrick <>
Date: Fri, 25 Mar 2005 13:10:54 -0500

Hi Chris,

On Mar 25, 2005, at 12:28 PM, Chris Allport wrote:

> When repaint() is called, does it simply redraw the current layer, or
> does
> it try to redraw all layers?

All the layers are redrawn when a layer.repaint() method is called.

> In a BufferedMapBean application with multiple layers, does it make
> sense to
> allow each layer to call repaint() as they change, or should one,
> single
> repaint() be called after all layers are updated?

You have no accurate information available to you to make that
assessment. Layers are quite independent, and you can't assume that
their requests for painting mean they are in a stable state. In
theory, only a layer knows what it's supposed to be showing at any
given time. If it's told to render before it's ready, it should draw
nothing, and call for a repaint when it has something new to display.

> In reviewing EditableOMGraphic, it seems that when the object is moved:
> - the entire map is marked dirty - map.setBufferDirty(true)

Only when the drawing tool is finished. Not while it's being edited.
The map is marked dirty to clean up anything left over from the XOR
rendering from the drawing tool, and also to render the modified
OMGraphic in it's place in the layer that had it changed. The
OMDrawingTool paints that EditableOMGraphic on top of the map when it's
being moved. If the receiving layer isn't visible, or if it's covered
by other layers, the complete repaint needs to happen to get the layer
ordering correct.

> - all of the graphics are repainted -
> map.paintChildren(map.getGraphics())
> Now, if a user is dragging an object around, they obviously cannot be
> dragging around multiple objects, so maybe regerating the whole map
> during a
> drag makes sense.

That shouldn't be happening during a drag. The drag should be XOR
rendering some lightweight representation of the objects around on top
of the map, with a repaint happening when all of the editing is

> However, what is the best way to manage repaint() in an
> application with multiple graphics on multiple layers that are
> constantly
> updated?

Move the unchanging layers to the background layer in the
BufferedLayerMapBean, and use a timer to limit update map repaints to
specific intervals for the changing layers, maybe having a separate
repaint2() method that works with a centralized timer object. You
still want the main repaint() method to work in response to projection

- Don

Don Dietrick,
BBN Technologies, Cambridge, MA

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Received on Fri Mar 25 2005 - 13:11:40 EST

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