From: Rhett Aultman <rhett@meraki.com>
Date: Sat, 4 Jan 2020 06:04:56 +0000 (-0500)
Subject: Slight tweak to lab 5 to make the character move
X-Git-Url: https://git.kitaultman.com/?a=commitdiff_plain;h=9b64e61194cda5bec3f77852466fb9f50dfd46d2;p=nes_coding.git

Slight tweak to lab 5 to make the character move

Marching in place isn't nearly as exciting as using the OAM for its
real power, which is moving sprites around the screen, so this is a little
tweak to demonstrate updating the OAM coordinates.
---

diff --git a/src/.sprite.asm.swp b/src/.sprite.asm.swp
deleted file mode 100644
index fa72341..0000000
Binary files a/src/.sprite.asm.swp and /dev/null differ
diff --git a/src/sprite.asm b/src/sprite.asm
index efe9317..8c9bd6b 100644
--- a/src/sprite.asm
+++ b/src/sprite.asm
@@ -87,9 +87,9 @@
 current_frame:
   .byte 0
 sprite_x:
-  .byte 0
+  .byte $7F
 sprite_y:
-  .byte 0
+  .byte $7F
 frame_count:
   .byte 0
 
@@ -167,9 +167,6 @@ zero_oam:
 ; and frame index (i.e. where in the animation we are)
 ; and then call load_sprite to do the hard work
 
-  lda #$7F
-  sta sprite_x
-  sta sprite_y
   lda #0
   sta current_frame
   lda #0
@@ -207,7 +204,7 @@ nmi:
   sta frame_count
 
 ; We counted 15 NMIs, so let's update the animation frame and
-; make the little character walk in place
+; make the little character walk
   lda current_frame
   clc                   ; NEVER forget to clear the carry flag before adding
   adc #6                ; Each frame is an offset of a multiple of 6
@@ -216,6 +213,14 @@ nmi:
   lda #0
 dont_cycle_anim:
   sta current_frame
+
+
+  lda sprite_x
+  clc
+  adc #4
+  sta sprite_x
+dont_reset_x:
+  sta sprite_x
 done:
   jsr load_sprite
   rti                   ; Return from the NMI (NTSC refresh interrupt)
@@ -228,8 +233,6 @@ done:
   ldx #0
   ldy current_frame
   lda #$7F
-  sta sprite_x
-  lda #$7F
   sta sprite_y
 load_loop:
 ; First of two cells
@@ -265,6 +268,7 @@ load_loop:
   inx
   lda sprite_x
   sta SPRITE_PAGE, X
+  sec
   sbc #7              ; return to the left cell
   sta sprite_x
   inx
@@ -272,6 +276,7 @@ load_loop:
   cpx #24
   bne load_loop
   lda sprite_y
+  sec
   sbc #14
   sta sprite_y
   rts