From 0ec1e0e15e57dee075c2d14fc812f3f95ebbd3ca Mon Sep 17 00:00:00 2001
From: Tom Morton <tomm@riseup.net>
Date: Mon, 26 Jun 2023 21:14:18 +0100
Subject: [PATCH] Implement INKEY with negative argument

INKEY with a negative argument tests if the given fabgl virtual key
(-arg) is currently held down. This is done with a keyboard state
map maintained using an experimental mos_setkbvector OS call.
(https://github.com/tomm/agon-mos/tree/mos_setkbvector)
---
 eval.asm  | 19 +++++++++++++++++++
 patch.asm | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/eval.asm b/eval.asm
index d2c60e7..7a9dc93 100644
--- a/eval.asm
+++ b/eval.asm
@@ -85,6 +85,7 @@
 			XREF	OSKEY
 			XREF	INKEY1
 			XREF	GETPORT
+			XREF	KBSTATE
 ;
 ; BINARY FLOATING POINT REPRESENTATION:
 ;    32 BIT SIGN-MAGNITUDE NORMALIZED MANTISSA
@@ -1144,6 +1145,8 @@ GET1:			SCF
 ;
 INKEYS:			CALL    ITEMI
 			EXX
+			BIT 7,H
+			JR NZ, INKEY_NEG
 			CALL    OSKEY
 INKEY1:			LD      DE,ACCS
 			LD      (DE),A
@@ -1151,6 +1154,22 @@ INKEY1:			LD      DE,ACCS
 			RET     NC
 			INC     E
 			RET
+; negative INKEY argument: See if that key is currently down
+INKEY_NEG:
+			XOR		A
+			LD 		H, A
+			SUB		L		; +ve keycode in A
+			LD		L, A
+			LD		B, A
+			LD		DE, KBSTATE
+			ADD		HL, DE
+			LD		A, (HL)	; non-zero if key is pressed
+			OR		A
+			SCF
+			JR		Z, INKEY1
+			LD		A, B
+			JP		INKEY1
+
 ;
 ;MID$ - Return sub-string.
 ;Result is string.
diff --git a/patch.asm b/patch.asm
index 21825c9..96b3541 100644
--- a/patch.asm
+++ b/patch.asm
@@ -65,6 +65,7 @@
 			XDEF	OSSAVE
 			XDEF	EXPR_W2
 			XDEF	GETPORT
+			XDEF	KBSTATE
 
 			XREF	ASC_TO_NUMBER
 			XREF	RAM_START
@@ -302,7 +303,8 @@ LTRAP1:			LD	HL,FLAGS 		; Escape is pressed at this point, so
 ;            Z-flag reset indicates AUTO-RUN.
 ;  Destroys: A,D,E,H,L,F
 ;
-OSINIT:			CALL	VBLANK_INIT
+OSINIT:			CALL	VBLANK_INIT 
+			CALL KBVECTOR_INIT
 			XOR	A
 			LD	(FLAGS), A		; Clear flags and set F = Z
 			LD 	HL, USER
@@ -310,6 +312,56 @@ OSINIT:			CALL	VBLANK_INIT
 			LD	E, A			; Page boundary
 			RET	
 
+KBVECTOR_STOP:
+			LD.L HL, 0
+			LD C,0  ; do not extend HL with MB: we want it zeroed
+			LD A, 1Dh
+			RST.LIS 8
+			RET
+
+KBVECTOR_INIT:
+			LD HL,KBVECTOR
+			LD C,1  ; extend HL to 24-bits using MB
+			LD A,1Dh
+			RST.LIS 8
+			RET
+
+			.ASSUME	ADL = 1
+KBVECTOR:
+			PUSH IY
+			PUSH IX
+			PUSH DE
+			POP IX
+			
+			LD.SIS DE,0
+			LD.SIS HL,KBSTATE
+			LD E, (IX+2)				; key code
+			
+			; coerce upper case letters to lower case, otherwise there are issues with stuck keys when shift is used
+			LD A,E
+			SUB 48
+			JR C, $F
+			CP 26
+			JR NC, $F
+			LD A, E
+			SUB 26
+			LD E, A
+			
+$$:
+			ADD.S HL,DE
+			
+			LD A, (IX+3)				; key down
+			LD.SIS (HL),A
+			
+			POP IX
+			POP IY
+			RET
+
+			.ASSUME	ADL = 0
+
+KBSTATE:
+			DS 256
+
 ;
 ;OSCLI - Process a MOS command
 ;
@@ -404,6 +456,7 @@ COMDS:  		DB	'BY','E'+80h		; BYE
 ; *BYE
 ;
 STAR_BYE:		CALL	VBLANK_STOP		; Restore MOS interrupts
+			CALL	KBVECTOR_STOP
 			POP.LIL	IX 			; The return address to init
 			LD	HL, 0			; The return code
 			JP	(IX)