From 1d041e2d573279326c3c82488e83f84967fc6dfd Mon Sep 17 00:00:00 2001
From: Alex Janka <alex@alexjanka.com>
Date: Mon, 6 Feb 2023 11:42:45 +1100
Subject: [PATCH] gpu improvements

---
 src/processor/gpu.rs | 40 +++++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 19 deletions(-)

diff --git a/src/processor/gpu.rs b/src/processor/gpu.rs
index 2715744..cb6a3e2 100644
--- a/src/processor/gpu.rs
+++ b/src/processor/gpu.rs
@@ -15,16 +15,25 @@ enum TilemapArea {
     T9C00,
 }
 
+impl TilemapArea {
+    fn get_offset(&self) -> u16 {
+        match self {
+            TilemapArea::T9800 => 0x9800,
+            TilemapArea::T9C00 => 0x9C00,
+        }
+    }
+}
+
 enum TiledataArea {
     D8000,
-    D8800,
+    D9000,
 }
 
 impl TiledataArea {
     fn get_addr(&self, addr: u8) -> u16 {
         match self {
             TiledataArea::D8000 => 0x8000 + (addr as u16),
-            TiledataArea::D8800 => 0x8800_u16.wrapping_add_signed(as_signed(addr) as i16),
+            TiledataArea::D9000 => 0x9000_u16.wrapping_add_signed(as_signed(addr) as i16),
         }
     }
 }
@@ -45,7 +54,7 @@ struct LCDC {
     bg_window_enable: bool,
 }
 
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 enum Colour {
     White,
     LightGray,
@@ -159,7 +168,7 @@ impl CPU {
             tile_area: if get_bit(reg, 4) {
                 TiledataArea::D8000
             } else {
-                TiledataArea::D8800
+                TiledataArea::D9000
             },
             bg_tilemap: if get_bit(reg, 3) {
                 TilemapArea::T9C00
@@ -261,15 +270,15 @@ impl CPU {
         offset_y: u8,
     ) {
         let tile_line = (scanline as usize) + (offset_y as usize);
-        let tile_row = tile_line / 8;
-        let tile_px = ((tile_line as u16) % 8) * 2;
-        let row_addr = (tile_row * 32) as u16 + get_tilemap_offset(tilemap);
+        let tilemap_row = tile_line / 8;
+        let tile_px = (tile_line) % 8;
+        let tiledata_offset = tile_px * 2;
+        let row_addr = (tilemap_row * 32) as u16 + tilemap.get_offset();
         for x in 0..32 {
-            let tile_addr = self.memory.get(row_addr + x) + tile_px as u8;
-            let lsbs = self.memory.get(tiledata.get_addr(tile_addr));
-            let msbs = self.memory.get(tiledata.get_addr(tile_addr + 1));
-            // let lsbs = self.memory.get(row_addr + tile_px + (x * 2));
-            // let msbs = self.memory.get(row_addr + tile_px + (x * 2) + 1);
+            let tile_addr =
+                tiledata.get_addr(self.memory.get(row_addr + x)) + tiledata_offset as u16;
+            let lsbs = self.memory.get(tile_addr);
+            let msbs = self.memory.get(tile_addr + 1);
             for px_x in 0..8 {
                 let lsb = get_bit(lsbs, px_x);
                 let msb = get_bit(msbs, px_x);
@@ -304,13 +313,6 @@ fn scale_buffer(buffer: &Vec<u32>, width: usize, height: usize, factor: usize) -
     v
 }
 
-fn get_tilemap_offset(tilemap: &TilemapArea) -> u16 {
-    match tilemap {
-        TilemapArea::T9800 => 0x9800,
-        TilemapArea::T9C00 => 0x9C00,
-    }
-}
-
 fn bits_to_mapped_colour(lsb: bool, msb: bool, palette: Palette) -> Colour {
     match (lsb, msb) {
         (true, true) => palette.three,