From 526bc9e32031afd206a8ceba486205c16d64cf4d Mon Sep 17 00:00:00 2001
From: Colin McMillen <c@16bit.cc>
Date: Sun, 31 May 2015 18:03:46 -0400
Subject: [PATCH] Spawn enemy shots from right edge of screen.

---
 pewpew.asm | 37 +++++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/pewpew.asm b/pewpew.asm
index f8b1b25..a1354d6 100644
--- a/pewpew.asm
+++ b/pewpew.asm
@@ -467,6 +467,7 @@ MaybeShootDone:
 
 UpdateWorld:
     jsr UpdateShotCooldown
+    jsr SpawnEnemyShots
     jsr UpdateShotPositions
     jsr UpdateBackgroundScroll
     rts
@@ -485,6 +486,38 @@ UpdateShotCooldown:
 
 
 
+SpawnEnemyShots:
+    lda vBlankCounter
+    bit #%00111111
+    beq +
+    rts
++
+    lda #8  ; Sprite number.
+    sta enemyShotArray
+
+    lda #254
+    sta enemyShotArray + 1  ; x.
+
+    lda #((224 - 32) / 2)
+    and #%01111111
+    sta enemyShotArray + 2  ; y.
+
+    lda #-6
+    sta enemyShotArray + 3  ; x-velocity.
+
+    GetRandomByte
+    and #%00000111  ; [0, 7]
+    clc
+    adc #-3  ; [-3, 4]
+    cmp #4
+    bne +
+    lda #0  ; [-3, 3] with 2x chance of zero.
++
+    sta enemyShotArray + 4  ; y-velocity.
+    rts
+
+
+
 UpdateShotPositions:
     ldx #0
 
@@ -553,7 +586,7 @@ ShotDone:
     .rept shotSize
         inx
     .endr
-    cpx #(playerShotArrayLength * shotSize)
+    cpx #(playerShotArrayLength * enemyShotArrayLength * shotSize)
     bne UpdateShot
 
     rts
@@ -653,7 +686,7 @@ UpdateSprites:
     .rept shotSize
         iny
     .endr
-    cpy #(playerShotArrayLength * shotSize)
+    cpy #((playerShotArrayLength + enemyShotArrayLength) * shotSize)
     bne -
 
     ; Now clear out the unused entries in the sprite table.