Assembly experiment: bouncing block

Expert (101)

02-05-2021, 15:44

Hi all,

I've been working on little program written in assembly that displays a bouncing block on a MSX1 computer.
And here it is: https://msxpen.com/codes/-MZhICPdfzZSbUFti9cO

What I notice is that it runs very smooth on an American NTSC machine (60 Hz) but not on an European PAL machine (50 Hz). Seems that 10 Hz is a big difference for smoothness? Never realized that.

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Van MsxKun

Paragon (1112)

02-05-2021, 16:13

Pbk71 wrote:

What I notice is that it runs very smooth on an American NTSC machine (60 Hz) but not on an European PAL machine (50 Hz). Seems that 10 Hz is a big difference for smoothness? Never realized that.

It is!
That's why games at 25/30 are most of cases unnaceptable

Van bore

Master (156)

02-05-2021, 16:25

50Hz should look smooth.

If it seems stuttery it is likely because you are using a display that is fixed to 60Hz with a 50Hz video signal.
Make sure you are connecting your MSX to a screen that is capable of both 50Hz and 60Hz to get a valid comparison.

Van aoineko

Paladin (809)

02-05-2021, 16:39

In your case, it is more a speed difference than smoothness.
If you want to compare "smoothness" you should implement frequency detection and move 20% more when the VDP is at 50 Hz.
But with normal human eyes, it's hard to see any difference between 50 and 60 Hz.

Van Grauw

Ascended (10683)

02-05-2021, 16:38

It is what Bore said. The issue is that you're looking at it on an emulator with a 60 Hz display.

Van Daemos

Paragon (2028)

02-05-2021, 17:02

Quote:

That's why games at 25/30 are most of cases unnaceptable

25 bad. 30 just goes fine. You can take my word on that.

Van Pbk71

Expert (101)

02-05-2021, 21:30

Ok, thanks for the advice. I've only used WebMSX for this experiment and when I look at Quick Options there I see that the option for NTSC/PAL is set to AUTO. I will try some other emulators too te see the difference.
In the meanwhile I've added a multicolored sprite to it. It's a bouncing coin now although it bounces like a ball
https://msxpen.com/codes/-MZiXWv_XZVC5QrpSdYN

Van ARTRAG

Enlighted (6915)

02-05-2021, 21:54

Your code looks a bit clumsy but works, nice effect.
A few general suggestions to improve your code:
- Try to remove the use of AND A / SBC HL,DE and use only ADD, resorting to the fact that speed can be negative.
- Use the sign of speed (its highest bit) as flag for the direction and remove dir
- Use RST DCOMPR to call DCOMPR
- Use the fact that the VDP vram pointer auto-increments each time you send a byte
e.g. this could replace your i/o write code

ld hl,SPRITEAT 
call SETWRT
ld c,98h
ld a,(y+1)		; y-coördinate = high byte of word y
out (c),a
ld a,(x)	    ; x-coördinate
out (c),a
ld a,(pattern)
out (c),a
ld a,(color)
out (c),a

Van Pbk71

Expert (101)

03-05-2021, 10:20

Quote:

Your code looks a bit clumsy but works, nice effect.
A few general suggestions to improve your code:

@ARTRAG: Thanks for your comment and suggestions. I really appreciate these suggestions and I will try to implement them in my experiment.

I'm quite new to Z80 assembly and programming a MSX with assembly so I will probably do many things in a not so convenient way. I'm using Google a lot to find all kind of code examples and use them in my own code. As I am used to programming in higher level languages it's a challenge for me to 'translate' high level programming routines to assembly. But I'm getting there and I was already very proud to get this running. Time for some optimization now

Van Pbk71

Expert (101)

03-05-2021, 21:25

For my optimization I want to change the sign of my variable speed (dw).
So for two's complement I've got to xor it with 0xFFFF and then add 1.

To do this for a word in memory I've now written this code:

        ld de,(test)
        ld a, d
        xor 0xFF
        ld d,a
        ld a, e
        xor 0xFF
        ld e,a
        inc de 
        ld (test),de
test:   dW 0x1000

I've tested it and it seems to work. Is this the most fast way to do this?

Van Daemos

Paragon (2028)

03-05-2021, 21:42

        ld a,(test+1)
   ;     ld a, d
    ;    xor 0xFF
       cpl
        ld d,a
        ld a, (test)
     ;   xor 0xFF
      cpl
        ld e,a
        inc de 
        ld (test),de
test:   dW 0x100

should shave of 4 Tstates if I calculated it right