core/gpu: Fix bitmap mode displaying invalid sprites

fixes #107


Former-commit-id: 4b307c80f0519a5034dad1188d285cb44a2c8eeb
Former-commit-id: 8879aababad1aef0690adb0a88cdeb36368c024a

rustboyadvance-core/src/gpu/mod.rs

@@ -51,6 +51,9 @@ pub mod consts {
     pub const CYCLES_FULL_REFRESH: usize = 280896;
 
     pub const TILE_SIZE: u32 = 0x20;
+
+    pub(super) const VRAM_OBJ_TILES_START_TEXT: u32 = 0x1_0000;
+    pub(super) const VRAM_OBJ_TILES_START_BITMAP: u32 = 0x1_4000;
 }
 pub use self::consts::*;
 
@@ -201,6 +204,8 @@ pub struct Gpu {
     pub vram: BoxedMemory,
     pub oam: BoxedMemory,
 
+    pub(super) vram_obj_tiles_start: u32,
+
     #[debug_stub = "Sprite Buffer"]
     pub obj_buffer: Vec<ObjBufferEntry>,
 
@@ -230,6 +235,8 @@ impl Gpu {
             bldalpha: BlendAlpha(0),
             bldy: 0,
 
+            vram_obj_tiles_start: VRAM_OBJ_TILES_START_TEXT,
+
             state: HDraw,
             vcount: 0,
             cycles_left_for_current_state: CYCLES_HDRAW,
@@ -244,6 +251,21 @@ impl Gpu {
         }
     }
 
+    pub fn write_dispcnt(&mut self, value: u16) {
+        let new_dispcnt = DisplayControl(value);
+        let old_mode = self.dispcnt.mode();
+        let new_mode = new_dispcnt.mode();
+        if old_mode != new_mode {
+            debug!("[GPU] Display mode changed! {} -> {}", old_mode, new_mode);
+            self.vram_obj_tiles_start = if new_dispcnt.mode() >= 3 {
+                VRAM_OBJ_TILES_START_BITMAP
+            } else {
+                VRAM_OBJ_TILES_START_TEXT
+            };
+        }
+        self.dispcnt = new_dispcnt;
+    }
+
     pub fn skip_bios(&mut self) {
         for i in 0..2 {
             self.bg_aff[i].pa = 0x100;
@@ -543,12 +565,7 @@ impl Bus for Gpu {
                 if ofs > 0x18000 {
                     ofs -= 0x8000;
                 }
-                let obj_offset = if self.dispcnt.mode() >= 3 {
-                    0x14000
-                } else {
-                    0x10000
-                };
-                if ofs < obj_offset {
+                if ofs < self.vram_obj_tiles_start {
                     self.vram.write_16(ofs & !1, expand_value(value));
                 }
             }

rustboyadvance-core/src/gpu/render/obj.rs

@@ -98,6 +98,9 @@ impl Gpu {
         }
 
         let tile_base = OVRAM - VRAM_ADDR + 0x20 * (attrs.2.tile() as u32);
+        if tile_base < self.vram_obj_tiles_start {
+            return;
+        }
 
         let (tile_size, pixel_format) = attrs.tile_format();
         let palette_bank = match pixel_format {
@@ -191,6 +194,9 @@ impl Gpu {
         }
 
         let tile_base = OVRAM - VRAM_ADDR + 0x20 * (attrs.2.tile() as u32);
+        if tile_base < self.vram_obj_tiles_start {
+            return;
+        }
 
         let (tile_size, pixel_format) = attrs.tile_format();
         let palette_bank = match pixel_format {

rustboyadvance-core/src/iodev.rs

@@ -161,7 +161,7 @@ impl Bus for IoDevices {
         }
 
         match io_addr {
-            REG_DISPCNT => io.gpu.dispcnt.0 = value,
+            REG_DISPCNT => io.gpu.write_dispcnt(value),
             REG_DISPSTAT => io.gpu.dispstat.0 = value | (io.gpu.dispstat.0 & 7),
             REG_BG0CNT => io.gpu.backgrounds[0].bgcnt.0 = value,
             REG_BG1CNT => io.gpu.backgrounds[1].bgcnt.0 = value,