From 551aa135ec54c4343f04b3f6936f7959f780cde2 Mon Sep 17 00:00:00 2001
From: RochesterX <trevorisaacmaze@gmail.com>
Date: Fri, 15 May 2026 11:23:10 -0400
Subject: [PATCH] Granular scroll nametable updating, buffering and pointers,
 etc.

---
 plat.nes | Bin 40976 -> 40976 bytes
 plat.s   | 126 ++++++++++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 101 insertions(+), 25 deletions(-)

diff --git a/plat.nes b/plat.nes
index 40f80265618c61cfda6db0e07bfd5947fc1b241d..0888289378e59bf7a50a43ef4e99ff1079bd275d 100644
GIT binary patch
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diff --git a/plat.s b/plat.s
index e5da8a6..d3fad20 100644
--- a/plat.s
+++ b/plat.s
@@ -408,6 +408,8 @@ var_m:    .res 1
 var_n:    .res 1
 var_o:    .res 1
 var_p:    .res 1
+var_wide1:.res 2
+var_wide2:.res 2
 
 jump_pressed_last_frame: .res 1
 
@@ -415,15 +417,15 @@ frame_counter: .res 1
 last_frame_jumped: .res 1
 last_frame_moving: .res 1
 
-column_pattern:    .res 1
-tile_update_pos_r: .res 1
-tile_update_pos_l: .res 1
+column_pattern_pointer:    .res 2
+tile_update_pos: .res 1
 
 pointer:           .res 2
 
 .segment "BSS"
 level:      .res 240
 level2:     .res 240
+room_buffer: .res 240
 
 .segment "CODE"
 main:
@@ -448,6 +450,8 @@ main:
 
     jsr init_objects
 
+    jsr update_room_buffer
+
 @loop:
     lda $2002
     lda frame_counter
@@ -695,7 +699,7 @@ init_objects:
 
     lda #0
     sta camera_speed
-    sta tile_update_pos_r
+    sta tile_update_pos
 
     rts
 
@@ -1474,30 +1478,58 @@ check_column_update:
     lsr
     lsr
 
-    cmp tile_update_pos_r
+
+    ; Thought: Level layout will be decoded from somewhere into the room_buffer_r or _l buffers, then they will be indexed into by this to load their column patterns
+
+    cmp tile_update_pos
     bne :+
-        ; Load column pattern
-        lda tile_update_pos_r
-        sta column_pattern
+        jsr load_column_pattern
 
         ; Apply pattern
         jsr update_nmt_column
 
-        ; Increment tile_update_pos_r
-        lda tile_update_pos_r
+        ; Increment tile_update_pos
+        lda tile_update_pos
         clc
         adc #1
         and #%00011111
-        sta tile_update_pos_r
+        sta tile_update_pos
     :
 
     rts
 
+load_column_pattern:
+    ; Based on tile update pos r, use that row to index in to the room buffer. Columns in the room buffer are stored as rows for sequential access.
+    ;
+    ; IDEA: Do we only need one tile update position? If for example we're going right and updating there, we don't need to do anything going left until that point is reached again on the left side. But it's the same point. It's the "seam" in the level. Maybe just an offset by one or something.
+    lda #<room_buffer
+    sta column_pattern_pointer
+    lda #>room_buffer
+    sta column_pattern_pointer+1
+
+    ; Since column pattern pointer points to the current column we need to draw, we start it at the beginning of the room buffer (which stores columns as rows), then we add 16 (going to the next "row" in memory which is the next column in reality) how many ever times in column_pattern_pointer to point to the correct row. From there, anything can just loop 16 times from that pointer to get the currently drawing row.
+    lda tile_update_pos
+    and #%00001111
+    tax
+    :
+        lda column_pattern_pointer
+        clc
+        adc #16
+        sta column_pattern_pointer
+        lda column_pattern_pointer+1
+        adc #0
+        sta column_pattern_pointer+1
+
+        dex
+        cpx #0
+        bne :-
+    rts
+
 update_nmt_column:
     ; X represents the row of the current tile being updated
     ldx #0
     @row_loop:
-        lda tile_update_pos_r
+        lda tile_update_pos
         clc
         ; Add offset in tiles from left edge of screen
         adc #16
@@ -1543,22 +1575,56 @@ update_nmt_column:
 
 
         ; Specifies what tile gets written to the column
-        lda column_pattern
-        rol
-        stx var_m
-        :
-            ror
-            dec var_m
-            dec var_m
-            bpl :-
+        ;
+        ;     T------>
+        ;lda column_pattern
+        ;ror
+        ;sta var_wide1
+        ;     >-----BX
+        ;lda column_pattern+1
+        ;ror
+        ;sta var_wide1+1
 
-        and #%00000001
-        cmp #0
-        beq :+
-            ora #%10000000
-        :
+        ;stx var_m
+        ;:
+            ;lda var_wide1+1
+            ;rol
+            ;sta var_wide1+1
+            ;lda var_wide1
+            ;rol
+            ;sta var_wide1
+            ;dec var_m
+            ;bpl :-
+
+        ;lda var_wide1
+        ;and #%10000000
+        ;cmp #0
+        ;beq :+
+            ; What metatile do we load for a non-empty shape?
+            ;lda #%10000001
+        ;:
+
+        ; Preserve Y (our index in to level)
+        tya
+        pha
+
+        ; Transfer X to Y (our current row in the updated column)
+        txa
+        tay
+
+        ; Instead of all that nonsense constructing the tile that we want to draw, just index in to the column_pattern_pointer
+        ; Storing in var wide 1 because I know it's not used
+        lda (column_pattern_pointer), Y
+        sta var_wide1
+
+        ; Restore Y
+        pla
+        tay
+        ; Write our new metatile to level (for collision mostly)
+        lda var_wide1
         sta (pointer), Y
 
+        ; ...and actually perform a nametable update
         and #%01111111
         ldy #5
         jsr mul_y
@@ -1619,6 +1685,16 @@ update_nmt_column:
 
     rts
 
+update_room_buffer:
+    ldx #0
+    :
+        lda default_level2, X
+        sta room_buffer, X
+        inx
+        cpx #240
+        bne :-
+    rts
+
 mul_x:
     cmp #0
     beq @zero