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AppGameKit Classic Chat / Timer Based Alpha

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bjadams
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Posted: 31st Oct 2011 13:41
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I have sprites that I want to fade away.
I am using Alpha.

However I want them to fade away at a constant rate, if the game plays at 60fps or 30fps, etc...

I thought of using the same concept as time based movement. But somehow the results are strange and irregular.

Does anyone have any experience on the subject and can illuminate me?
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baxslash
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Posted: 31st Oct 2011 15:53
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I use something like this:


Set a time when it should no longer be visible then reduce the alpha based on the current time.

(untested code)

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bjadams
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Posted: 31st Oct 2011 20:06
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I was using GetFrameTime() to increase Alpha values!
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baxslash
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Posted: 1st Nov 2011 10:45
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That might be unreliable as you might get a compounding error. Using an end time that you track from the timer is more stable.

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bjadams
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Posted: 1st Nov 2011 11:56
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Even for X & Y movement, you think GetFrameTime() is unreliable?
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baxslash
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Posted: 1st Nov 2011 12:14
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Just not as accurate.

I could be wrong but it seems like testing the difference between the last frame and the current one wouldn't be as accurate.

Logically it might be wrong as small floats are more accurate than large floats but maybe some testing would be a good idea?

I just prefer to measure increments from a fixed point rather than one at a time to avoid cumulative errors. In the real world it tends to be more accurate but I'm not 100% certain when it comes to this specific situation...

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bjadams
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Posted: 1st Nov 2011 16:30
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I followed the simplest route and used GetFrameTime()

Fingers crossed I hope this works quite ok overall.
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Mobiius
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Posted: 1st Nov 2011 20:14
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I checked these and GetFrameTime() was exactly the same as the whole ( LastFrame# - CurrentFrame# ) I use for my timer based mavement in all my apps, AppGameKit and DBP.

My signature is NOT a moderator plaything! Stop changing it!
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bjadams
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Posted: 1st Nov 2011 21:52
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Yes I made the same tests and printed the values, and the multiplier flats are the same.

Having a timer multiplier is good for X & Y movements, but for ANGLES and ALPHA I am doing something wrong as with 30fps the angle value is obviously bigger than with 60fps, so the sprite rotates more!

I need to find another solution!
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