Re: Creating a radar sweep effect
Re: Creating a radar sweep effect
- Subject: Re: Creating a radar sweep effect
- From: Graham Cox <email@hidden>
- Date: Sun, 27 Sep 2009 16:50:24 +1000
Hi John,
The difficulty with this kind of display is simulating the persistence
of the old cathode-ray tubes in a realistic way. Just drawing a shadow
is unlikely to work, though it might help get you some way by creating
the glow caused by scattering.
One possibility is to use OpenGL. It has a "history buffer" mode (may
not be called that - I forget exactly) that stores the previous image
at a diminished brightness and that can be stacked for a series of
frames, giving a fade or trail effect.
Alternatively you can model persistence yourself by buffering up
several frames (for example, using a NSBitmapImageRep) and then
drawing the stack for each frame followed by the latest content. I
have used this approach to simulate an oscilloscope display and it
works well in terms of realism, but performance can be an issue.
You'll probably need to store at least 3 or 4 "previous" frames to get
the effect you want - there's no really good way to do it in one pass
and get realism. Fact is those old tubes literally stored the image in
the phosphors which naturally faded in their own time after the beam
passed - to simulate that realistically requires that you model the
image storage.
--Graham
On 27/09/2009, at 11:19 AM, John Cebasek wrote:
Hi All:
I'm wondering what the best way to create a radar sweep effect is?
(Like in old war movies?)
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