diff options
| author | Miquel Sabaté Solà <mssola@mssola.com> | 2026-03-06 16:06:56 +0100 |
|---|---|---|
| committer | Miquel Sabaté Solà <mssola@mssola.com> | 2026-03-06 16:06:56 +0100 |
| commit | f3737201eda72e51730a0762be98598fee08d86b (patch) | |
| tree | 5dd72353503b84f1024dea2423bfdd247c42bea6 | |
| parent | b01c36807ec2fd07e21fac03cc201b2832425cf9 (diff) | |
| download | jetpac.nes-f3737201eda72e51730a0762be98598fee08d86b.tar.gz jetpac.nes-f3737201eda72e51730a0762be98598fee08d86b.zip | |
Fix a cycling bug when shooting carelessly
When shooting like crazy and killing random enemies, after a while a
cycling bug would appear which would make enemies to turn in weird
directions, die unexpectedly, and other weird shenanigans.
This comes back to commit 7c493ba3f338 ("Improve a bit the performance
on enemy death"), which removed the saving/restoring of the value on the
'y' register. That being said, this register was actually being needed
at least by Bullets::update(), so in certain situations this register
might have a bad value (e.g. via the Explosions::create() call).
Fixes: 7c493ba3f338 ("Improve a bit the performance on enemy death")
Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>
| -rw-r--r-- | .nasm/segments.txt | 2 | ||||
| -rw-r--r-- | src/enemies.s | 13 |
2 files changed, 14 insertions, 1 deletions
diff --git a/.nasm/segments.txt b/.nasm/segments.txt index 2367e2f..f89b010 100644 --- a/.nasm/segments.txt +++ b/.nasm/segments.txt @@ -1,4 +1,4 @@ - HEADER: 16/16 (100%) -- ROM0: 6448/32762 (19.68%) +- ROM0: 6452/32762 (19.69%) - ROMV: 6/6 (100%) - ROM2: 8192/8192 (100%) diff --git a/src/enemies.s b/src/enemies.s index facb255..7097af5 100644 --- a/src/enemies.s +++ b/src/enemies.s @@ -613,7 +613,16 @@ .endproc ;; The enemy has been set to dust, remove it. + ;; + ;; NOTE: the 'x' register is modified, the 'y' register is _preserved_. .proc bite_the_dust + ;; This function might be called by loops which abuse index + ;; registers. Luckily that's not the case for the 'x' register, but at + ;; least the loop on Bullets::update() does heavy use of the 'y' + ;; register. Preserve it now on the stack. + tya + pha + ;; Invalidate this enemy. lda #$FF ldx Enemies::zp_pool_index @@ -634,6 +643,10 @@ ldx Enemies::zp_pool_index sta Enemies::zp_enemies_pool_base + 3, x + ;; Restore back the value for the 'y' register. + pla + tay + rts .endproc |