sortof bounds-check while moving

[ld45_start_nothing] / src / main.asm

diff --git a/src/main.asm b/src/main.asm
index c3ab902..a5e0754 100644 (file)
--- a/src/main.asm
+++ b/src/main.asm
@@ -5,6 +5,8 @@
 %include "intr.inc"
 %include "dbglog.inc"
 
+PLAYER_MOVE_SPEED equ 5
+
        ; this is placed at the beginning of our binary at 1mb (see game.ld)
        ; and it's what gets executed directly by the boot loader
        section .startup
@@ -41,19 +43,36 @@ main_loop:
        jmp main_loop
 
 update:
+       mov eax, [ship_y]
+
        check_key SC_W
        jnc .not_w
-       dec dword [ship_y]
+       sub eax, PLAYER_MOVE_SPEED
+       jns .not_w
+       xor eax, eax
 .not_w:        check_key SC_S
        jnc .not_s
-       inc dword [ship_y]
-.not_s: check_key SC_A
+       add eax, PLAYER_MOVE_SPEED
+       cmp eax, 200 << 8
+       jb .not_s
+       mov eax, 200 << 8
+.not_s:
+       mov [ship_y], eax
+       mov eax, [ship_x]
+
+       check_key SC_A
        jnc .not_a
-       dec dword [ship_x]
+       sub eax, PLAYER_MOVE_SPEED
+       jns .not_a
+       xor eax, eax
 .not_a: check_key SC_D
        jnc .not_d
-       inc dword [ship_x]
+       add eax, PLAYER_MOVE_SPEED
+       cmp eax, 320 << 8
+       jb .not_d
+       mov eax, 320 << 8
 .not_d:
+       mov [ship_x], eax
        ret
 
        section .data