From af193ba5d6ff096b19c7f67d4da696cf0e1dedcd Mon Sep 17 00:00:00 2001
From: John Tsiombikas <nuclear@member.fsf.org>
Date: Tue, 16 Jan 2024 08:13:58 +0200
Subject: [PATCH] constrained parallax scrolling

---
 src/data.s       |    2 ++
 src/part_dna.c   |   15 +++++++++++++++
 src/part_simba.c |   40 ++++++++++++++++++++++++++++++++++------
 3 files changed, 51 insertions(+), 6 deletions(-)

diff --git a/src/data.s b/src/data.s
index c36ae73..81ebd47 100644
--- a/src/data.s
+++ b/src/data.s
@@ -12,6 +12,8 @@
 	.globl simbabg_cmap_end
 	.globl simbabg_tmap
 	.globl simbabg_tmap_end
+	.globl simbafg_data
+	.globl simbafg_data_end
 	.globl simbafg_cmap
 	.globl simbafg_cmap_end
 	.globl simbafg_tmap
diff --git a/src/part_dna.c b/src/part_dna.c
index 2b5b6aa..af6bc98 100644
--- a/src/part_dna.c
+++ b/src/part_dna.c
@@ -36,6 +36,21 @@ void dna_init(void)
 
 void dna_start(void)
 {
+	short i;
+
+	/* setup tilemaps */
+	vdp_setup_addr(VDP_VRAM, 0xc000);	/* nametable A */
+	for(i=0; i<2048; i++) {
+		VDP_DATA = 0;
+	}
+	vdp_setup_addr(VDP_VRAM, 0xe000);	/* nametable B */
+	for(i=0; i<2048; i++) {
+		VDP_DATA = 0;
+	}
+
+	vdp_setup_addr(VDP_VRAM, 0xf000);	/* hscroll table is at f000, see vdp.S */
+	VDP_DATA = 0;
+	VDP_DATA = 0;
 }
 
 void dna_update(void)
diff --git a/src/part_simba.c b/src/part_simba.c
index a10e5fd..ea6f3ae 100644
--- a/src/part_simba.c
+++ b/src/part_simba.c
@@ -3,12 +3,19 @@
 #include "vdp.h"
 #include "pad.h"
 #include "parts.h"
+#include "debug.h"
+
+#define BGTILES_OFFS		1
+#define FGTILES_OFFS		4
 
 extern uint16_t simbabg_data[], simbabg_data_end[];
 extern unsigned char simbabg_cmap[], simbabg_cmap_end[];
 extern uint16_t simbabg_tmap[], simbabg_tmap_end[];
+extern uint16_t simbafg_data[], simbafg_data_end[];
+extern unsigned char simbafg_cmap[], simbafg_cmap_end[];
+extern uint16_t simbafg_tmap[], simbafg_tmap_end[];
 
-static int scroll;
+static short scroll;
 
 void simba_init(void)
 {
@@ -16,10 +23,16 @@ void simba_init(void)
 
 	/* upload tiles */
 	src = simbabg_data;
-	vdp_setup_addr(VDP_VRAM, 32);	/* start from tile 1 32 bytes on */
+	vdp_setup_addr(VDP_VRAM, BGTILES_OFFS * 32);	/* start from tile 1 32 bytes on */
 	while(src < simbabg_data_end) {
 		VDP_DATA = *src++;
 	}
+
+	src = simbafg_data;
+	vdp_setup_addr(VDP_VRAM, FGTILES_OFFS * 32);
+	while(src < simbafg_data_end) {
+		VDP_DATA = *src++;
+	}
 }
 
 void simba_start(void)
@@ -29,10 +42,15 @@ void simba_start(void)
 	unsigned char *cptr;
 
 	/* setup tilemaps */
+	src = simbafg_tmap;
+	vdp_setup_addr(VDP_VRAM, 0xc000);	/* nametable A */
+	while(src < simbafg_tmap_end) {
+		VDP_DATA = VDP_TILENAME(*src++ + FGTILES_OFFS, 3, 0);
+	}
 	src = simbabg_tmap;
 	vdp_setup_addr(VDP_VRAM, 0xe000);	/* nametable B */
 	while(src < simbabg_tmap_end) {
-		VDP_DATA = VDP_TILENAME(*src++ + 1, 2, 0);
+		VDP_DATA = VDP_TILENAME(*src++ + BGTILES_OFFS, 2, 0);
 	}
 
 	/* setup colormaps */
@@ -41,23 +59,33 @@ void simba_start(void)
 		vdp_setcolor(2, i, cptr[0] >> 4, cptr[1] >> 4, cptr[2] >> 4);
 		cptr += 3;
 	}
+	cptr = simbafg_cmap;
+	for(i=0; i<16; i++) {
+		vdp_setcolor(3, i, cptr[0] >> 4, cptr[1] >> 4, cptr[2] >> 4);
+		cptr += 3;
+	}
 
 	/* set scrolling to whole screen */
 	vdp_setreg(VDP_REG_MODE3, 0);
+	scroll = 0;
+	vdp_setup_addr(VDP_VRAM, 0xf000);	/* hscroll table is at f000, see vdp.S */
+	VDP_DATA = 0;
+	VDP_DATA = 0;
 }
 
 void simba_update(void)
 {
 	if(bnstate & PAD_LEFT) {
-		if(scroll > 0) scroll--;
+		if(scroll < 0) scroll++;
 	} else if(bnstate & PAD_RIGHT) {
-		if(scroll < 511) scroll++;
+		if(scroll > -192) scroll--;
 	}
+	dbgval[0] = scroll;
 }
 
 void simba_vblank(void)
 {
 	vdp_setup_addr(VDP_VRAM, 0xf000);	/* hscroll table is at f000, see vdp.S */
-	VDP_DATA = 0;
 	VDP_DATA = scroll;
+	VDP_DATA = scroll >> 1;
 }
-- 
1.7.10.4