Less than 50 fps...?

[pmc]

Good morning people.

If I have an effect that will run in 50fps (or 60fps - hi there NTSC guys ) then I can do what I do now and just have a copper triggered level 3 interrupt for it and everything's nicely synced with the display.

But, what happens when an effect won't run in 50fps and I need more time...?

What are the strategies for syncing with the display while running at a lower frame rate...?

As always, apologies if this is a really stupid question.

[StingRay]

Originally Posted by pmc

What are the strategies for syncing with the display while running at a lower frame rate...?

First of all, try to optimize your code so it may run in 50 FPS. If that isn't possible, then you can either cheat (that's what demo coding is all about anyway) or remove your routine from the interrupt and call it in a normal "Wait for vblank, do effect" loop, f.e.

LOOP    bsr WaitRaster
    bsr lame_and_slow_effect ; ;D
    btst #6,$bfe001
    bne.b LOOP
    rts

WaitRaster
.wait    move.l $dff004,d0
    and.l #$1ff00,d0
    cmp.l #303<<8,d0    ; 303 = line to wait for
    bne.b .wait
    rts

[pmc]

Originally Posted by StingRay

First of all, try to optimize your code so it may run in 50 FPS.

Originally Posted by StingRay

    bsr lame_and_slow_effect ; ;D

I just read those and roared with laughter - thanks man.

Let me assure you that this is hypothetical slow effect! I was just interested in what to do in this situation.

While we're on the subject of waiting for vbl - I understand your wait for vbl code just fine (in fact, thanks to your generosity it's the identical routine that's now part of my standard code ) but where did you get line 303 from...?

Again this is probably a very stupid question and I just didn't read the HRM properly or something but where is it stated that line 303 == start of vbl...?

[oRBIT]

Just curious, is that WaitVbl-code valid for both NTSC/PAL Amigas?

[StingRay]

Originally Posted by pmc

While we're on the subject of waiting for vbl - I understand your wait for vbl code just fine (in fact, thanks to your generosity it's the identical routine that's now part of my standard code ) but where did you get line 303 from...?

This is just shortly before the VBlank starts to give a bit more time for the code. Since line 303 is not visible anymore there are no problems. Only valid for a standard PAL display of course.

Originally Posted by oRBIT

Just curious, is that WaitVbl-code valid for both NTSC/PAL Amigas?

No, it's PAL only.