Questions re: Efficient blitting

[earok]

A little bit of background on my work in progress game
[ Show youtube player ]

It's AGA, dual playfield with 4 bitplanes on each playfield. The background layer contains the trees, grass etc, and essentially is never drawn to (except for permanent damage to the background, such as the bodies of the enemies).

The foreground layer is where the BOBs (in this case, the purple enemies - the player and his projectiles are sprites) are drawn to.



The current configuration is this - every frame, the BOB is wiped out with an erase blit (to prevent it leaving trails), and redrawn, simple as that. I don't use BBlit because I don't need to keep what was there previously, there's nothing on the foreground playfield except for the BOBs themselves.

So my questions are these:
- I don't really need a "cookie" mask shape, as the BOBs are essentially square and shouldn't overlap with each other - in other words, I don't mind at all if a previously opaque pixel is wiped out by a transparent pixel on the BOB. Is there a way of blitting without "cookie" masks in Blitz, and do you get a performance gain from this?
- In addition to the above, if say I had a 1 pixel transparent border around my BOB, and only moved it by no more than 1 pixel per frame - would this negate the need for having an erase blit at all if it was being blitted without a mask?
- Is there anything else that I can do that might boost blitter performance? For reference, the minimum target of the game will be a stock AGA machine (2mb, 68020)


Thanks in advance

[Havie]

Looking good!

In answer to your question, looking through my Blitz manual you should use Blit Shape#.X.Y and as you say cookie mode is on. The other modes can be selected by using BlitMode but I don't think any of them will be or use as they are either erasemode, invmode and solidmode.

Block shape#,X,Y is faster but restricts you to shapes that are multiples of 16 and position at mulitples of 16 (x position only so block could be useful for objects that move up and down the screen). Like the old ZX Speccy you could have preshifted bobs but this would mean that you would need 16 versions of each image and might be a memory problem (although if you have 16 frames of animation...)

I would have thought that just bliting using Blit and having a 1 pixel border would work fine - remember that in Blitz colour 0 is transparent.

[Cylon]

Originally Posted by earok

A little bit of background on my work in progress game

- Is there anything else that I can do that might boost blitter performance? For reference, the minimum target of the game will be a stock AGA machine (2mb, 68020)

About that cookie issue:
If you create your shapes with shapesmaker, there is an option in the menu for "make cookie" - uncheck it.

You can blit in any fancy way you like -
use the cmd 'blitmode ' to set the required minterms.
Useful values are already known as constants (well, not really)
SolidMode,
CookieMode and
EraseMode.

To speed up things:
If you're sure, the bobs will not interfere you can blit them all every frame without eraseblit and then use simple CLS to erase the whole bmap. I guess you use dblbuffer?

[earok]

Thanks guys, I did a few experiments and such.

It appears that I can do a straight blitter copy (without mask) by using a custom blitter mode, eg

#CopyMode=$DC0
BlitMode #CopyMode

(Though I'm not sure that's the optimal way to do it)

I've experiment with a bunch of different ways to wipe the enemies from the backbuffer and redraw them, the QBlit method appears to be the most efficient. I tried CLS but it's painfully slow (I guess because my backbuffer is 4 fullscreen bitplanes)

[Master484]

I've experiment with a bunch of different ways to wipe the enemies from the backbuffer and redraw them, the QBlit method appears to be the most efficient. I tried CLS but it's painfully slow (I guess because my backbuffer is 4 fullscreen bitplanes)

Yes, the QBlit seems to be the fastest command to use with dual playfields. And the "Unqueue" command seems to clean the backbuffer quite fast.

I too have experimented with all sorts methods to make the unbuffering faster, but there aren't that many ways...CLS is slow, and so is full screen "filled Box" drawing. But I also tried this method: I drew everything with "Blit", and as usual had two Bitmaps for Buffering, but also made a third empty Bitmap, as large as the screen, filled with background color. And at the start of every frame I would "BlockScroll" the contents of this third Bitmap to my current Backbuffer, which achieved a "CLS" effect.

And I think this was a faster way of emptying the screen than doing a real CLS, but still way slower than a series of QBlit-Unqueues. Although in those cases when the screen was totally filled with BOBS, like about 50 large characters, it was faster to empty the backbuffer with the "BlockScroll-CLS", than doing "Unqueues" for 50 large BOBs. So in some cases this method might be useful, but only in games that would constantly draw extremely lot of stuff, and which would run around 20fps, such as BOB based 1st person shooters maybe?

And also it was interesting that when I tried the Blockscroll trick from a 1 bitplane Bitmap to a 3 bitplane Bitmap, it was a lot faster, but it only erased some colors of the BOBs, leaving other 2 bitplanes intact. This phenomenon could also be useful in some cases, but it could be hard to use in normal games.

[earok]

Thanks for that! I assumed all drawing commands were CPU based whereas BlockScroll etc is Blitter based, so that could be why..

I'm thinking of attempting a super simple Mario Kart engine, with just one bitplane for the track to keep 3D overhead to a bare minimum (UI and Karts would be rendered with sprites and a second playfield) that BlockScroll trick would probably be useful here.

[idrougge]

If you have a "clean" background buffer, you can use that as a source for restoration with Unqueue. Add the clean bitmap as a second parameter to Unqueue, such as:

Unqueue 1,3

[Master484]

If you have a "clean" background buffer, you can use that as a source for restoration with Unqueue. Add the clean bitmap as a second parameter to Unqueue

Thanks, I'll have to test this.

I'm thinking of attempting a super simple Mario Kart engine, with just one bitplane for the track to keep 3D overhead to a bare minimum (UI and Karts would be rendered with sprites and a second playfield) that BlockScroll trick would probably be useful here.

That sounds possible, although still the blockscroll method is rather slow, and 50fps most likely isn't possible to achieve if it's used. Although I've only tested it on an A500 setup, it might be faster on an A1200.

One game idea that I've been thinking about is basically Doom, but made like Backlash:
http://hol.abime.net/12

So there would be no walls or real levels, just lots of enemies and action. I think that even A500 could run it at 50fps, with occasional slowdowns. A dual playfield setup would be used for speed, and when the action gets too hot, then maybe the Blockscroll trick + Frameskip could save the day.

[earok]

Originally Posted by Master484

Thanks, I'll have to test this.
That sounds possible, although still the blockscroll method is rather slow, and 50fps most likely isn't possible to achieve if it's used. Although I've only tested it on an A500 setup, it might be faster on an A1200.

Well.. I'll give it a go. It's only one bitplane I want to clear, and even then at most it'd be only the lower half of the screen (320x128).

If it's not 50FPS on A500 then I suppose I could make the project AGA only. Though it'd be nice if it was OCS, so far as I know there's no OCS Mario Kart clone (I don't count games like Bump N Burn that have Outrun style turning, and of course Xtreme Racing was AGA only).

[earok]

Digging this up again because I had a further question -

Is it possible (or even a good idea to?) easily disable blitter waits? I was thinking of using the blitter interrupt to let the game know when it's safe to draw again, and while it's still waiting to be able to draw it'd instead do game logic things etc (so program flow would only halt if it attempted to draw another Bob, but there was already a Bob render outstanding)

[Shatterhand]

Sorry Earok, I can't answer your question, though I am curious if someone can answer it too.

If you're sure, the bobs will not interfere you can blit them all every frame without eraseblit and then use simple CLS to erase the whole bmap

Are you sure clearing the whole bitmap is faster than clearing just parts of it ? I don't think QBlit is slower than Blit, it's just "slower" because you have to erase the shape before drawing it again (which is necessary anyway)

Clearing the whole screen is a good idea if it's actually faster than erasing just the necessary shapes. I tried it before, but without using a Double Buffer, so the bitmap became basically garbage.

Though that's something really easy to check out.

[idrougge]

CLS doesn't seem to be the optimal way of clearing the screen. There is a vector graphics example in the Examples directory which uses a piece of inline assembly to clear the screen instead.