Real Time Screen Effects - GameCreators Forum

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Sad Professor

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Posted: 17th Jun 2005 20:46

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I'm after the quickest method of grabbing a section of the screen and applying some effects to the section (mainly changeing the values of the pixels) and then pasting it back on the screen - I've tried doing this using the 'get image' and turning the image into a sprite so I can use alpha, but this seems incredibly slow to do every frame - and I've been warned off doing this using memblocks - anyone any ideas?

Cheers

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BatVink

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Posted: 17th Jun 2005 22:55 Edited at: 17th Jun 2005 22:57

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Memblocks is the only solution faster than GET IMAGE. You can actually dump the screen straight to a memblock, and dump it back again afterwards....

+ Code Snippet

mem = screen width() * screen height() * 4

make memblock 1, mem
copy memory get memblock ptr(1), get pixels pointer(), mem

...

lock pixels
copy memory get pixels pointer(), get memblock ptr(1), mem
unlock pixels

That could actually be faster than using GET IMAGE on small sections of the screen.beacuse it uses direct memory manipulation.

You should make the memblock before you get into your main code loop.

BatVink

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Sad Professor

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Posted: 17th Jun 2005 23:02

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But...I have tried this and it proved slow - I posted another topic on this (search: slow memblocks?) and people have told me its slow as I am using main memory as opposed to gpu and its passing from main to gpu which is why its slowing down.....I'm getting a lot of mixed opinions on this.

I'm starting to think that if you use memblocks you pay an initial penalty for the transfer from main memory to gpu, but after that actual calculations on it are faster that get image etc. So if you are going to be using memblocks then make sure that you are making hte most of them (ie a lot of drawing operations) to make them worthwhile because of the performance hit.
Does this make sense?
cheers

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Hamish McHaggis

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Posted: 17th Jun 2005 23:28

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If you're using a camera, and not wanting to capture sprites or other images, then use SET CAMERA TO IMAGE. The quickest way then would be through some sort of plugin probably, as there is no low level access to images withDBPro except through memblocks.

More tea Vicar?

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Sad Professor

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Posted: 17th Jun 2005 23:32

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I'm using it for 2d stuff currenty - is my assumption correct that using memblocks will mean taking a hit during access but realtively speaking operations are faster?

Should I be using memblocks for real time effects?

THanks again

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Raven

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Posted: 18th Jun 2005 00:29

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Depends on what R/T Effects your talking about.

Personally I wouldn't waste the processor time with even convering to a memblock.

It's far quicker to use direct memory.

+ Code Snippet

Global BackBufferPtr, EffectBufferPtr, SizeOfBackBuffer As Integer
BackBufferPtr = Get Pixels Pointer()
SizeOfBackBuffer = Screen Pitch() * Screen Height() * (Screen Depth() / 8)

EffectBufferPtr = Make Memory(SizeOfBackBuffer)
Copy Memory EffectBufferPtr, BackBufferPtr, SizeOfBackBuffer

...

Lock Pixels
Copy Memory BackBufferPtr, EffectBufferPtr, SizeOfBackBuffer
UnLock Pixels

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Three Score

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Posted: 18th Jun 2005 01:35

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i knew it!
raven would bring up the backbuffer

but yes writing straight to the buffer is fast(no memory moving)

now if only there was a way to switch buffers like in blitz basic

http://free-space.myftp.org/thread1.html

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BatVink

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Posted: 18th Jun 2005 02:09 Edited at: 18th Jun 2005 02:10

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What's the difference speedwise between making memory and making a memblock?

And a second question...can you write words and dwords to memory, like you can with memblocks, or just bytes?

You still have the problem of moving from GPU to memory though, don't you?

BatVink

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BatVink

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Posted: 18th Jun 2005 02:24

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Quote: "Posted: 7th Sep 2004 17:46

--------------------------------------------------------------------------------
Memblocks are approx 2-3x slower than using Data Pointers.
Memblock creation itself is actually EXTREMELY costly timewise, so try to make sure your memory you use is constant to get better speed rather than constant init/free.

That said they're not exactly sluggish (unless you look at other languages), should be fast enough for most things.
"

BatVink

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Raven

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Posted: 18th Jun 2005 03:01

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Data Pointers will shift the data size that you use to move them

e.g.

+ Code Snippet

Type BufferType
 B As Byte
 W As Word
 D As Dword
EndType

Global Address As Integer
Global Buffer As BufferType

Address = Make Memory(4)

*Address = 0x55FFAA88

Buffer.B = *Address
Buffer.W = *Address
Buffer.D = *Address

Print Buffer.B
Print Buffer.W
Print Buffer.D

Wait Key
Delete Memory Address

erm. lol well that didn't work quite right but you get the idea ^_^

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DarkBASIC Professional Discussion / Real Time Screen Effects