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Old 18 October 2020, 00:46   #1
a1k3k
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Help with smooth 3D Cube in C on A500 using Draw() and Move()

As a challenge, I've taken it upon myself to delve into Amiga coding in C and attempt to make a few 3D routines.

Is it possible to create a decently smooth wireframe rotating cube using C that runs on a stock A500?

I ask because I've seen [ Show youtube player ] and it seems he's managed to do it using pure C, but I haven't managed to do so yet.


In my own attempt, I've tried double buffering (swapping out two bitmaps every frame). The flicker is reduced, but the frame rate is still abysmally slow, something like 1-2 frames per second.

Even when I turn off rotation and just have basic horizontal movement, it's slow. On a souped-up UAE config it's smooth though.

So I reckon it's nothing to do with the transformation parts, which are integer and use lookup tables for trig functions.

I'm using a 320x200 screen with 2 bitplanes.

My cube is pretty much self-explanatory:

struct node cubeNodes[8] = {{-1, -1, -1},{-1, -1, 1},{-1, 1, -1},{-1, 1, 1},{1, -1, -1},{1, -1, 1},{1, 1, -1},{1, 1, 1}};


struct edge cubeEdges[12] = {{0, 1},{1, 3},{3, 2},{2, 0},{4, 5},{5, 7},{7, 6},{6, 4},{0, 4},{1, 5},{2, 6},{3, 7}};


My bitmap swapper:

void swapBitmap(){
static int bitmap = 0;

if (bitmap==0) {
rp.BitMap = &b2;
ri.BitMap = &b2;
SetRast(&rp,0);
bitmap=1;
} else {
rp.BitMap = &b;
ri.BitMap = &b;
SetRast(&rp,0);
bitmap=0;
}
}


where rp is the RastPort and ri is RastInfo.

My copper list updater:

void updateCopperLists() {
MakeVPort (&v, &vp);
MrgCop (&v);
LoadView (&v);
WaitTOF();
WaitBlit();
}


and finally, my draw routine which basically iterates through the object edges and does a Move() on the first vertex and a Draw() on the second vertex. On entry it swaps in the bitmap on which it'll draw on, and prior to exit updates the copper list so the bitmap is shown:

     swapBitmap();

for (i = 0; i < obj->edgeSize; i++)
{

/* Draw line using screen coordinates */
Move (&rp,
obj->nodes[obj->edges[i].nodeA].x + WIDTH / 2 + obj->centerAt.x,
-obj->nodes[obj->edges[i].nodeA].y + HEIGHT / 2 + obj->centerAt.y);
Draw (&rp, obj->nodes[obj->edges[i].nodeB].x + WIDTH / 2 +
obj->centerAt.x, -obj->nodes[obj->edges[i].nodeB].y + HEIGHT / 2 +
obj->centerAt.y);
}
}

updateCopperLists();


FWIW I've also tried starting the main code with Forbid() and Disable() but it doesn't help speed up in any measurable sense.

Anyone has any tips? Maybe it's something I'm overlooking? I'm pretty new to coding for the Amiga but I'd love to keep at it and get better as I've always wanted to code my own demo routines that can run on a bog standard A500.

I'd like to move on to assembler later on, but first I'd like to be able to hash it out in C.
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Old 18 October 2020, 09:32   #2
Ernst Blofeld
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I think your updateCopperLists function may be doing more than it needs to. I don't think you should be calling MrgCop on every buffer flip. This example http://amigadev.elowar.com/read/ADCD.../node05B3.html certainly looks like it does less.

I have used the second method described here http://amigadev.elowar.com/read/ADCD.../node0346.html with success before, but can't find my code at the moment to demonstrate.

Last edited by Ernst Blofeld; 18 October 2020 at 09:46.
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Old 18 October 2020, 16:57   #3
Samurai_Crow
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The OS routines are abysmally slow. Interface directly with the hardware for a massive speed boost.
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Old 18 October 2020, 22:52   #4
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Quote:
Originally Posted by Ernst Blofeld View Post
I think your updateCopperLists function may be doing more than it needs to. I don't think you should be calling MrgCop on every buffer flip. This example http://amigadev.elowar.com/read/ADCD.../node05B3.html certainly looks like it does less.
The example uses Intuition's RethinkDisplay() which apparently does MrgCop() and LoadView(). Since I'm not using Intuition screens and bypassing it altogether, I just thought I'd do the same. Though you may be right that it probably shouldn't be called on every flip as they indicate in the RKM "WARNING: This routine can take several milliseconds to run, so do not use it lightly." but the example provided does not heed that.

Quote:
Originally Posted by Ernst Blofeld View Post
I have used the second method described here http://amigadev.elowar.com/read/ADCD.../node0346.html with success before, but can't find my code at the moment to demonstrate.
I've now tried this second method and it's still slow. Maybe a bit faster, but nothing usable.
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Old 18 October 2020, 22:55   #5
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Quote:
Originally Posted by Samurai_Crow View Post
The OS routines are abysmally slow. Interface directly with the hardware for a massive speed boost.
Any pointers on how to do that in C? I'm fairly new to Amiga coding (although an old hand with coding in general).
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Old 18 October 2020, 23:13   #6
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Quote:
Originally Posted by a1k3k View Post
The example uses Intuition's RethinkDisplay() which apparently does MrgCop() and LoadView(). Since I'm not using Intuition screens and bypassing it altogether, I just thought I'd do the same. Though you may be right that it probably shouldn't be called on every flip as they indicate in the RKM "WARNING: This routine can take several milliseconds to run, so do not use it lightly." but the example provided does not heed that.


I've now tried this second method and it's still slow. Maybe a bit faster, but nothing usable.
How fast is it if you remove everything except for the buffer swapping? ie leaving very little apart from LoadView swapping buffers? And, conversely, how fast is it if you just use single buffering? It would be useful to know where the overhead really is.
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Old 19 October 2020, 02:44   #7
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If you're using more than 2 bits per pixel, reduce the palette depth. This will speed up the blitter by freeing up bandwidth used by the display DMA. You should only need 3 foreground colors to draw a cube.
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Old 19 October 2020, 10:05   #8
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Looking at the youtube clip, he's not doing half the work you are. He's drawing into a single bitplane, probably clearing only the bits he's touched, and probably not using double buffering as he can probably sync with the display as he's drawing so little. I'm sure you can get your stuff to be smoother once you've worked out where the time is going, but I wouldn't compare to his.

You may want to check out the bartman gcc vs-code stuff that will allow you to profile in a modernish way.

Last edited by Ernst Blofeld; 19 October 2020 at 19:01.
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Old 19 October 2020, 16:48   #9
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Looking at the YouTube clip there are 2 playfields at 1 bitplane each. The Copper work is best done only once. A double-buffered one bitplane screen is easy when there are only 2 copper lists. The copper does all the bitplane changes too.
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Old 19 October 2020, 23:52   #10
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Quote:
Originally Posted by Ernst Blofeld View Post
How fast is it if you remove everything except for the buffer swapping? ie leaving very little apart from LoadView swapping buffers? And, conversely, how fast is it if you just use single buffering? It would be useful to know where the overhead really is.
So I included a little fps timer in the code and I get on my A1k 5-6 fps with absolutely nothing on, except buffer swap. With single buffer, I get a solid 6. OTOH on my 25MHz A3k I went from 25 to 43 fps.


Quote:
Originally Posted by Ernst Blofeld View Post
Looking at the youtube clip, he's not doing half the work you are. He's drawing into a single bitplane, probably clearing only the bits he's touched, and probably not using double buffering as he can probably sync with the display as he's drawing so little. I'm sure you can get your stuff to be smoother once you've worked out where the time is going, but I wouldn't compare to his.

You may want to check out the bartman gcc vs-code stuff that will allow you to profile in a modernish way.

Quote:
Originally Posted by Samurai_Crow View Post
Looking at the YouTube clip there are 2 playfields at 1 bitplane each. The Copper work is best done only once. A double-buffered one bitplane screen is easy when there are only 2 copper lists. The copper does all the bitplane changes too.
You're right guys, I absolutely missed the point that he's using a different approach. To start with, I'll probably try to cut down from 2 bitplanes to 1.

Thanks for all the insight, I appreciate it a lot!
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Old 20 October 2020, 04:27   #11
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Quote:
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5-6 fps with absolutely nothing on, except buffer swap
This is surprising to me, I would have expected even OS friendly code to do around 15 fps to do nothing.
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Old Yesterday, 15:04   #12
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Quote:
Originally Posted by Ernst Blofeld View Post
This is surprising to me, I would have expected even OS friendly code to do around 15 fps to do nothing.
So I screwed up big time in my earlier posts and FPS checks. I forget to comment out a call to a critical non-draw function: the rotation function. Yes, I know. I thought I had it commented out, but didn't.

Anyway, that function was the culprit. I was doing some math with doubles and that killed the speed. I changed it over to integer math and everything is way, way faster now and smooth as butter.

Here are some stats:
Screen is 320x256, 1 bitplane, 1 cube scaling, rotating and moving across the screen.

(A) Single buffer, no WaitTOF(): 30-31 with flicker
(B) Single buffer, 1 WaitTOF(): 25 fps solid with flicker
(C) Single buffer, 2 WaitTOF(): 16-17 fps with flicker

(D) Double buffer, no WaitTOF(): 30-31 without flicker
(E) Double buffer, 1 WaitTOF(): 25 fps solid without flicker
(F) Double buffer, 2 WaitTOF(): 16-17 fps without flicker

So out of the lot, D seems great. I guess B and E are at a constant 25 fps due to the WaitTOF() limiting refreshes.

Using 2 WaitTOF()'s decreases performance and is not required since I'm not using interlaced modes.

And without any work (no cube drawing and transformations):

(G) Single buffer, no WaitTOF(): 357 fps
(H) Single buffer, 1 WaitTOF(): 50 fps
(I) Single buffer, 2 WaitTOF(): 25 fps

(J) Double buffer, no WaitTOF(): 336 fps
(K) Double buffer, 1 WaitTOF(): 50 fps
(L) Double buffer, 2 WaitTOF(): 25 fps

For the double buffer swapper, all I do is set the LOFCprList, SHFCprList, RastInfo and RastPort bitmaps and then do a LoadView() (no MakeVPort() and MrgCop()).
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Old Yesterday, 15:32   #13
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Beam sync with WaitTOF can free up some processor time for other functions because, unlike PC, vertical blank triggers an interrupt on Amiga.
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Old Yesterday, 17:07   #14
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Quote:
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(D) Double buffer, no WaitTOF(): 30-31 without flicker
Maybe you want to move to triple buffering.
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