| Re: Expose Events (easy questions) [message #30026] |
Thu, 04 April 2002 09:59 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Ted Cary (tedcary@yahoo.com) writes:
> it's just hard to believe they'd make such claims
> in the documentation for no reason.
I guess you have never worked for a software company.
I can think of 10 reasons just off the top of my head. :-)
Cheers,
David
--
David W. Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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| Re: Expose Events (easy questions) [message #30028 is a reply to message #30026] |
Thu, 04 April 2002 08:38  |
Ted Cary
Messages: 53
Registered: October 2001
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Member |
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David Fanning wrote:
> If you want my opinion, I'd stay as far away
> from the APP_SCROLL keyword as possible.
The behavior on our Macs here has nothing to do with APP_SCROLL. I replaced
the APP_SCROLL switch with /VIEWPORT_EVENTS, /EXPOSE_EVENTS. No difference.
I've tested the program on 3 different Macs now, even an iMac, and the X field
of the expose event structure always contains the y screen size. Did anyone
else test this on a Macintosh?
I'm still wondering why the documentation says to use this technique "when
displaying images or anything else displayed in device units." It's supposed
to be "good for displaying large images because the entire image does not have
to be redrawn when viewport events are generated."
Is setting RETAIN to 0 and then handling expose and viewport motion events
really the correct what to deal with large images? The documentation makes it
sound like it's the preferred way, but nobody seems to have ever used it. I'll
write something to test if this method is really any better... it's just hard
to believe they'd make such claims in the documentation for no reason.
Thanks to everyone who took the time to test this out,
Ted Cary
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| Re: Expose Events (easy questions) [message #30060 is a reply to message #30028] |
Wed, 03 April 2002 09:49 |
Ted Cary
Messages: 53
Registered: October 2001
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Member |
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"David Fanning" <david@dfanning.com> wrote in message
news:MPG.1714eb51cd25064b989861@news.frii.com...
> Ted Cary (tedcary@yahoo.com) writes:
>
>
> But, that said, the values in IDL 5.4 Windows of the
> X and Y fields of the event structure are the locations
> of the lower-left corner of the window in viewport
> coordinates, which is exactly what I would expect.
That's what I expected too, but at least on my Mac at work the X field does
not appear to have anything to do viewport X-coordinates. It's the
scr_ysize, every time. I spent 3 hours toying with it yesterday, so I'm
pretty sure about it. I'll post the code later.
I was hoping that by using APP_SCROLL and then explicitly redrawing only the
viewable portion of the window that I would speed things up. Drawing a
larger image in an object graphics hierarchy to a scrollable window takes a
long time--noticeably longer than drawing a smaller image. My cursor lags
too much during drag-drawing with the mouse, when the hierarchy is redrawn
with every motion event. The lag is definitely proportional to image size.
The documentation for WIDGET_DRAW maintains that one should always use
APP_SCROLL with large images, and in fact with anything drawn in device
coordinates (I think). I was assuming this was because of the slowness
problem? If not, what's the point?
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| Re: Expose Events (easy questions) [message #30061 is a reply to message #30060] |
Wed, 03 April 2002 10:17 |
James Kuyper
Messages: 425
Registered: March 2000
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Senior Member |
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David Fanning wrote:
> Ted Cary (tedcary@yahoo.com) writes:
>
>
>> The APP_SCROLL draw widget is in a resizable base
>
>
> I have to admit, I don't get the APP_SCROLL keyword!
> On Windows, at least, it appears to disable the
> scrolling ability of the operating system and *makes*
> you scroll the image yourself. (Tell me again, *why*
> do I want to do that when you already take care of it!?)
>
> But, that said, the values in IDL 5.4 Windows of the
> X and Y fields of the event structure are the locations
> of the lower-left corner of the window in viewport
> coordinates, which is exactly what I would expect.
>
> It is no problem copying the right part of the image
> from a pixmap, or from the image itself, using these
> values. But I still don't understand why you would
> want to. (I guess if you were going from the image
> data directly it would make some sense. But then it
> wouldn't be particularly fast.)
I think the most reasonable use of this would be to implement something
that uses the same interface as scrolling, but does something different
from what the built-in does. For instance, a vertical scroll that takes
your through the sections of a document at a constant rate, even though
some sections are much larger than others. Or an image might be
displayed with different magnifications, depending upon which part
you're viewing.
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| Re: Expose Events (easy questions) [message #30063 is a reply to message #30060] |
Wed, 03 April 2002 09:35 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Ted Cary (tedcary@yahoo.com) writes:
> The APP_SCROLL draw widget is in a resizable base
I have to admit, I don't get the APP_SCROLL keyword!
On Windows, at least, it appears to disable the
scrolling ability of the operating system and *makes*
you scroll the image yourself. (Tell me again, *why*
do I want to do that when you already take care of it!?)
But, that said, the values in IDL 5.4 Windows of the
X and Y fields of the event structure are the locations
of the lower-left corner of the window in viewport
coordinates, which is exactly what I would expect.
It is no problem copying the right part of the image
from a pixmap, or from the image itself, using these
values. But I still don't understand why you would
want to. (I guess if you were going from the image
data directly it would make some sense. But then it
wouldn't be particularly fast.)
Cheers,
David
--
David W. Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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| Re: Expose Events (easy questions) [message #30065 is a reply to message #30063] |
Wed, 03 April 2002 09:09 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Ted Cary (tedcary@yahoo.com) writes:
> Anyone with experience using scrollable, resizable draw widgets and RETAIN=0
> should be able to answer these easily.
Leaves me out, sorry. :-(
> What is contained in the X and Y fields of the structure generated by a draw
> widget expose event ?
You've got me. The documentation is...well...the documentation. :-(
> The APP_SCROLL draw widget is in a resizable base. The expose events are
> generated when the base is resized
I don't understand how this can happen. Can
you provide more details about this?
> Finally, is this even the fastest way to scroll through a large image?
> That's the motivation behind using APP_SCROLL in the first place. Should I
> be using any other techniques as well, like DEVICE_COPYING from pixmaps or
> anything like that?
I haven't done this in a LONG time, but I used
a Device Copy from a much larger pixmap into
the smaller draw widget, using the values obtained
from the VIEWPORT event structure to tell me where
to start copying in my pixmap. It worked great, as
far as I remember. I haven't been able to find that
program, but I've changed computers several times
since I wrote it.
Do you have a simple example you can provide us to
fool around with?
Cheers,
David
--
David W. Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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