Add the skeleton code for enemies

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

3 files changed, 60 insertions, 0 deletions

diff --git a/src/driver.s b/src/driver.s
index 66846ac..3ed0536 100644
--- a/src/driver.s
+++ b/src/driver.s
@@ -86,6 +86,7 @@
     @load_player:
         jsr Player::init
         jsr Bullets::init
+        jsr Enemies::init
 
         ;; Initialize pause timer.
         lda #0
diff --git a/src/enemies.s b/src/enemies.s
new file mode 100644
index 0000000..ab67ccd
--- /dev/null
+++ b/src/enemies.s
@@ -0,0 +1,58 @@
+.segment "CODE"
+
+.scope Enemies
+    ;; Maximum amount of enemies allowed on screen at the same time.
+    ENEMIES_POOL_CAPACITY = 3
+
+    ;; The capacity of the bullets pool in bytes.
+    ENEMIES_POOL_CAPACITY_BYTES = ENEMIES_POOL_CAPACITY * 3
+
+    ENEMIES_INITIAL_X = $F0
+
+    ;; TODO: 3 bytes a la bullets
+    zp_enemies_pool_base = $60
+
+    zp_enemies_timer = $D0
+    zp_enemies_pool_size = $D1
+
+    .proc init
+        ldx #0
+        stx zp_enemies_timer
+
+        ldy #ENEMIES_POOL_CAPACITY
+    @enemies_init_loop:
+        lda #0
+        sta zp_enemies_pool_base, x
+
+        inx
+        lda #$80                ; TODO: random
+        sta zp_enemies_pool_base, x
+
+        inx
+        lda #ENEMIES_INITIAL_X
+        sta zp_enemies_pool_base, x
+
+        inx
+
+        dey
+        bne @enemies_init_loop
+
+        lda #ENEMIES_POOL_CAPACITY
+        sta zp_enemies_pool_size
+
+        rts
+    .endproc
+
+    ;; Definitions for all the enemy types. These are just the tile IDs for each
+    ;; case. Note that some of them have $FF, which is because they span 2
+    ;; sprites instead of 4.
+tiles:
+    .byte $26, $27, $36, $37
+    .byte $28, $29, $38, $39
+    .byte $24, $25, $34, $35
+    .byte $2A, $2B, $3A, $3B
+    .byte $31, $32, $FF, $FF
+    .byte $41, $42, $FF, $FF
+    .byte $2C, $2D, $3C, $3D
+    .byte $2E, $2F, $3E, $3F
+.endscope
diff --git a/src/jetpac.s b/src/jetpac.s
index ada5d1f..3b7ac18 100644
--- a/src/jetpac.s
+++ b/src/jetpac.s
@@ -41,6 +41,7 @@
 .include "background.s"
 .include "player.s"
 .include "bullets.s"
+.include "enemies.s"
 .include "title.s"
 .include "driver.s"
 .include "vectors.s"