From 0536d1924237d3a7bb28b74b10578552d19e99dc Mon Sep 17 00:00:00 2001
From: Alex Janka <alex@alexjanka.com>
Date: Sun, 26 Feb 2023 16:18:22 +1100
Subject: [PATCH] better zero checking

---
 src/processor/memory/mmio/gpu.rs             | 17 ++++-------------
 src/processor/memory/mmio/gpu/tile_window.rs |  2 +-
 src/processor/memory/mmio/gpu/types.rs       | 10 +++++-----
 3 files changed, 10 insertions(+), 19 deletions(-)

diff --git a/src/processor/memory/mmio/gpu.rs b/src/processor/memory/mmio/gpu.rs
index 15ab2a6..e1dc251 100644
--- a/src/processor/memory/mmio/gpu.rs
+++ b/src/processor/memory/mmio/gpu.rs
@@ -276,18 +276,12 @@ impl Gpu {
             let x_addr = if object.flags.x_flip { px_x } else { 7 - px_x };
             let lsb = get_bit(lsbs, x_addr);
             let msb = get_bit(msbs, x_addr);
-            let colour = match object.flags.palette {
+            let (colour, is_zero) = match object.flags.palette {
                 ObjPalette::Zero => self.obj_palette_0,
                 ObjPalette::One => self.obj_palette_1,
             }
             .map_bits(lsb, msb);
-            if colour
-                == match object.flags.palette {
-                    ObjPalette::Zero => self.obj_palette_0,
-                    ObjPalette::One => self.obj_palette_1,
-                }
-                .zero
-            {
+            if is_zero {
                 continue;
             }
             let x_coord_uncorrected = (object.x as usize) + (px_x as usize);
@@ -341,11 +335,8 @@ impl Gpu {
             let msbs = self.vram.get(tile_addr + 1);
             let lsb = get_bit(lsbs, 7 - tile_px_x);
             let msb = get_bit(msbs, 7 - tile_px_x);
-            let colour = self.bg_palette.map_bits(lsb, msb);
-
-            if lsb || msb {
-                self.is_bg_zero[x] = false;
-            }
+            let (colour, is_zero) = self.bg_palette.map_bits(lsb, msb);
+            self.is_bg_zero[x] = is_zero;
 
             self.buffer[(scanline as usize * WIDTH) + x] = colour.as_rgb();
         }
diff --git a/src/processor/memory/mmio/gpu/tile_window.rs b/src/processor/memory/mmio/gpu/tile_window.rs
index 4150cda..0699ddc 100644
--- a/src/processor/memory/mmio/gpu/tile_window.rs
+++ b/src/processor/memory/mmio/gpu/tile_window.rs
@@ -66,7 +66,7 @@ impl TileWindow {
                     let colour = palette.map_bits(lsb, msb);
 
                     self.sprite_buffer[real_px_x + (real_px_y * TILE_WINDOW_WIDTH)] =
-                        colour.as_rgb();
+                        colour.0.as_rgb();
                 }
             }
         }
diff --git a/src/processor/memory/mmio/gpu/types.rs b/src/processor/memory/mmio/gpu/types.rs
index a76de9f..abf829e 100644
--- a/src/processor/memory/mmio/gpu/types.rs
+++ b/src/processor/memory/mmio/gpu/types.rs
@@ -150,12 +150,12 @@ impl Palette {
             | (self.three.as_bits() << 6)
     }
 
-    pub(super) fn map_bits(&self, lsb: bool, msb: bool) -> Colour {
+    pub(super) fn map_bits(&self, lsb: bool, msb: bool) -> (Colour, bool) {
         match (lsb, msb) {
-            (true, true) => self.three,
-            (true, false) => self.one,
-            (false, true) => self.two,
-            (false, false) => self.zero,
+            (true, true) => (self.three, false),
+            (true, false) => (self.one, false),
+            (false, true) => (self.two, false),
+            (false, false) => (self.zero, true),
         }
     }
 }