Very Computer

Hi, All,

I have a problem. I am using DirectX 8.0's overlay to play
sequence of bitmaps. When a bright object in very dark
background, the bright object will leave trace of its
shadows in the background when its screen position changes
during play the sequence. Those shadows are not there when
I look at each bitmap by itself.

For my situation, when the figure itself is moving, there
is no shadows. Shadows are only happening when the figure
and background are not moving themselve, but their screen
positions change. I have tested them on DELL flat panel
1701 and Sony trinitron 20" monitor with Gforce 3 graphic
card.

Will appreciate any hint and help

Thanks.

Yi Zhang.

[Please do not mail me a copy of your followup]

Quote:>I have a problem. I am using DirectX 8.0's overlay to play
>sequence of bitmaps. When a bright object in very dark
>background, the bright object will leave trace of its
>shadows in the background when its screen position changes
>during play the sequence.

This is a property of the CRT phosphors.  They don't immediately turn
off when you switch from a full-white pixel to a completely black
pixel.  All CRT monitors will have this phenomenon, but depending on
the particular phosphor formulation some will exhibit more 'trails'
than others.  LCD displays do not have this characteristic since they
don't have phosphors, but they have other issues with their display
technology.
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I'm sure what you're seeing is real (not a monitor
artifact) because of some recent weird (cool) things I've
displayed by accident. If instead of Clear()ing the
device between frames you paint a screen-sized quad with
an alpha-containing texture you can manipulate the
blending ops to create persistent trails behind objects.
To avoid this, check that you either use device->Clear()
or find the logical error in your texture blending states.
Regards

characteristic since they

Quote:>don't have phosphors, but they have other issues with
their display
>technology.
>--
>Ask me about my upcoming book on Direct3D from Addison-
Wesley!
>  Direct3D Book http://www.xmission.com/~legalize/book/
>    Don't Support Spammers!  Boycott Fractal Painter 7!
>     http://www.xmission.com/~legalize/spammers.html
>.

[Please do not mail me a copy of your followup]

Quote:>I'm sure what you're seeing is real (not a monitor
>artifact) because of some recent weird (cool) things I've
>displayed by accident.

Well yes, if you don't Clear() the frame, then you're going to be left
with the previous frame's contents, unless you used the DISCARD swap
effect -- in which case you'd be left with junk.

However, because the original poster said this:

Quote:>>>[...] When a bright object in very dark
>>>background, the bright object will leave trace of its
>>>shadows in the background when its screen position
>changes
>>>during play the sequence.

I'm guessing its the monitor trail because he specifically notes that
this happens with bright objects only.
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After a more careful look, I realize that the shadows are
parts of a bitmap which will be shown, say, 10 bitmaps,
later.  It only happens areas where are in very dark color.

It seems to me Direct Draw has some kind of "intelegence"
which "knows" to not redaw pixels under certain shresholds.

Regards.

specifically notes that

Quote:>this happens with bright objects only.
>--
>Ask me about my upcoming book on Direct3D from Addison-
Wesley!
>  Direct3D Book http://www.xmission.com/~legalize/book/
>    Don't Support Spammers!  Boycott Fractal Painter 7!
>     http://www.xmission.com/~legalize/spammers.html
>.

After a more careful look, I realize that the shadows are
parts of a bitmap which will be shown, say, 10 bitmaps,
later.  It only happens areas where are in very dark color.

It seems to me Direct Draw has some kind of "intelegence"
which "knows" to not redaw pixels under certain shresholds.

Regards.

specifically notes that

Quote:>this happens with bright objects only.
>--
>Ask me about my upcoming book on Direct3D from Addison-
Wesley!
>  Direct3D Book http://www.xmission.com/~legalize/book/
>    Don't Support Spammers!  Boycott Fractal Painter 7!
>     http://www.xmission.com/~legalize/spammers.html
>.