I am still going strong with the AGI Interpreter

[Manannan]

Hello,

I am putting a quick post up to let the community know that I am still plugging away with my AGI interpreter.

I have an interpreter that is capable of script interpretation, as I am able to loop through the two introductory scripts of ‘King’s Quest III’ continuously without crashing.

This is a good test because it isn’t a simple intro.

Obviously though different games will use different subsets of instructions, and hence more testing will be required.

I have spent the past few months learning VERA with SlithyMatt: https://github.com/SlithyMatt/x16-assembly-tutorial. I would recommend this tutorial, it is really good.

I have applied this knowledge and begun the drawing of the backgrounds. The line drawing works, and I have started work on flooding.

I want to give credit to Petri Hakkinen for his excellent pixel plotting algorithm: https://gist.github.com/petrihakkinen/c ... dcc582ecc2

It can be called in simple loop to draw lines and it is really fast. I would recommend anyone drawing lines or plotting points to consider it.

line drawing.png (136.19 KiB) Viewed 7747 times

[desertfish]

The line drawing only supports 256x256 coordinates it seems. Is that the resolution of the game as well?
Also - I can't get that routine to work properly. The stepping seems to halt after just 1 or 2 steps, or have a wrong angle. Have you changed anything about it to make it work?

btw I found this https://github.com/EgonOlsen71/bresenha ... aphics.asm it seems to include a flood fill routine.

[Manannan]

Hi,

The resolution is 160x168; although pixels are doubled in AGI (hence the 320 x 168 screen size).

Here is my code here; note my code is designed to be called from C, hence the popax and popa sub. calls. However these can easily be removed.

Thanks for sending me that link about the flood fill algorithm. I too a good read of it.

I am half way through translating the existing C AGI fill algorithm into assembly (C too slow obviously).

If I hit a wall I will come back to it.

I do appreciate your help.

Code: Select all

	;*****************************************************************
		; negate accumulator
		;*****************************************************************

neg:		eor #$ff
		clc
		adc #1
		rts

		;*****************************************************************
		; init bresenham line 
		;*****************************************************************
bresenham_sx: .byte $0 
bresenham_err: .word $0
bresenham_x1: .byte $0
bresenham_x2: .byte $0
bresenham_y1: .byte $0
bresenham_y2: .byte $0
bresenham_dx: .word $0
bresenham_sy: .byte $0
bresenham_dy: .word $0

b11Init_Bresenham:
		; dx = abs(x2 - x1)
		; dy = abs(y2 - y1)
		; sx = x1 < x2 ? 1 : -1
		; sy = y1 < y2 ? 1 : -1
		; err = dx > dy ? dx : -dy
		; dx = dx * 2
		; dy = dy * 2

		; if y1 < y2:
		; 	sy = 1
		; 	dy = y2 - y1
		; else:
		; 	sy = -1
		; 	dy = y1 - y2
		ldx #$ff		; X = -1
		lda bresenham_y1
		sec
		sbc bresenham_y2	; A = y1 - y2
		bpl :+
		ldx #1			; X = 1
		jsr neg			; A = y2 - y1
:		sta bresenham_dy
		stx bresenham_sy

		; if x1 < x2:
		; 	sx = 1
		; 	dx = x2 - x1
		; else:
		; 	sx = -1
		; 	dx = x1 - x2
		ldx #$ff		; X = -1
		lda bresenham_x1
		sec
		sbc bresenham_x2	; A = x1 - x2
		bpl :+
		ldx #1			; X = 1
		jsr neg			; A = x2 - x1
:		sta bresenham_dx
		stx bresenham_sx

		; err = dx > dy ? dx : -dy
		;lda bresenham_dx
		cmp bresenham_dy	; dx - dy > 0
		beq :+
		bpl @skiperr
:		lda bresenham_dy
		jsr neg
@skiperr:	sta bresenham_err

		; dx = dx * 2
		; dy = dy * 2
		asl bresenham_dx
		asl bresenham_dy
		rts

		;*****************************************************************
		; step along bresenham line
		;*****************************************************************

_b11Drawline:
		sta bresenham_y2
		jsr popax
		sta bresenham_x2
		stx bresenham_y1
		jsr popa
		sta bresenham_x1


        PSET bresenham_x1, bresenham_y1
		jsr b11Init_Bresenham

		; err2 = err

        drawLineStart:
		lda bresenham_err
		pha			; push err2

		; if err2 > -dx:
		;   err = err - dy
		;   x = x + sx
		clc
		adc bresenham_dx	; skip if err2 + dx <= 0
		bmi :+
		beq :+
		lda bresenham_err
		sec
		sbc bresenham_dy
		sta bresenham_err
		lda bresenham_x1
		clc
		adc bresenham_sx
		sta bresenham_x1
:
		; if err2 < dy:
		;   err = err + dx
		;   y = y + sy
		pla			; pop err2
		cmp bresenham_dy	; skip if err2 - dy >= 0
		bpl :+
		lda bresenham_err
		clc
		adc bresenham_dx
		sta bresenham_err
		lda bresenham_y1
		clc
		adc bresenham_sy
		sta bresenham_y1
:

        PSET bresenham_x1, bresenham_y1

        lda bresenham_x1
        cmp bresenham_x2
        beq @checkX
        jmp drawLineStart

        @checkX:
        lda bresenham_y1
        cmp bresenham_y2
        beq @endDrawLine
        jmp drawLineStart

    @endDrawLine:
rts

[Xiphod]

REALLY looking forward to this!!

And I hope you're able to (somehow) incorporate the PCjr or Tandy 3-voice audio. The CoCo3 AGI port is nice visually, but the audio would be a true step up to the experience - maybe 8MHz now lets us do it?

Here is an example of Tandy 3-voice audio in 1987 on King's Quest 2:
https://www.youtube.com/watch?v=uoMMu4GUNV0
(think Tandy 1000 and PCjr both used Texas Instrument SN76489 sound chip - no idea how easily X16 can approximate that)

The intro on the PCjr version of King's Quest 1 has a very brief nice audio (and a few moments in gameplay) [same Tandy 1000 version ]

I believe King's Quest 4 was the "first game" to have Adlib audio support (1988) - not fully sure how true that is (perhaps just on IBM PC side of things, and of course of Commercial game titles). Some of the 5.25" floppy disks releases of KQ4 I don't think had these files (and/or I think there was both an AGI and SCI release of KQ4, maybe just the SCI one had the Adlib support -- I'm not too excited about Adlib emulation, it always sounded a little bland to me; but Tandy multi-voice would be neat). I think KQ4 also had Roland MT32 support.


Need help? Tandy CoCo discord, maybe can find some of the folks who did AGI on the CoCo (under OS-9). Or I think some good audio folks here, might be able to look at the audio data files Sierra used and see if anything can be done with it. Al Lowe (credited with the music for KQ2) also still responds to emails.

[ahenry3068]

The Yamaha chip has 15 voices. I don't think emulating the Tandy 3 voice sound will be that difficult.

And my first computer was a 1000 TX. Sometimes I wish I still had it.

[kelli217]

The Yamaha chip has 8 voices, the VERA PSG has 16 voices plus a PCM channel. I don't think it will be all that difficult to handle the audio.

[ahenry3068]

Oh.... I should always go back and check DOCS before posting Tech Specs. .

It wasn't a deliberate Lie though , Just the Old Timers kicking in

[Xiphod]

Hmm, I wasn't worried about number of voices, but just the pitch/tone and actual sound and such, and whatever trickery had to be done to pull off on the PC (timing wise, inline with whatever the AGI stuff is doing). But I guess just capturing the notes and redoing it is fine (i.e. not necessarily looking for emulated sound, but capturing the audio mood of the original s/w). Just as the graphics side is an interpretation of the original AGI "scripting" (not sure if fair to call it a script, but it describes the "3d-ness" of each game scene {what you can walk in front of and behind, etc}, as far as I understand it).


Thexder had some nice sound on the Tandy 1000 also. Ken Williams writes about it in his recent 2020 book, I think it was one of Sierra's first Japanese developer collaborations. And similarly, the CoCo3 port of Thexder lost that great audio.
https://www.youtube.com/watch?v=Zw1YZt6Ml8w
H Godai did the Thexder audio
https://vgmdb.net/artist/5219
And much better C64 remixes of that audio exist.
https://soundcloud.com/andy_l/ne7-hibik ... r-c64-6581

[Manannan]

Thank you very much for your support.

It means the world to me when there are people are looking forward to it as I spend hours and hours coding this.

Tandy 3-voice audio would be a very good idea but it's still a long way in the future.
I've got to get the graphics working correctly first.