1 files changed, 53 insertions, 9 deletions

diff --git a/src/main.c b/src/main.c
index b8f2334..793baa8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -10,23 +10,58 @@
 //
 
 // TODO: Cleanup OBJ/OAM memory copying and access.
+//
+#define CBB_0  0
+#define SBB_0 28
 
-int main(void) {
-    // Load background palette.
-    memcpy(&PAL_BUFFER_BG[0], &bg_palette, 512);
-    memcpy(&TILE_MEM[0][0], bg_data, 3168);
-    memcpy(&SCREENBLOCK_MEM[30][0], bg_map, 2048);
-
-    // Configure BG0 to use 4bpp, 64x32 tile map in charblock 0 and screenblock
-    // 31.
-    BG_CTRL_0 = BG_CHARBLOCK(0) | BG_SCREENBLOCK(30) | BG_SIZE(0);
+#define CROSS_TX 15
+#define CROSS_TY 10
+
+u16 *bg0_map = SCREENBLOCK_MEM[SBB_0];
+
+void
+init_map() {
+    // initialize a background
+    BG_CTRL_0 = BG_CHARBLOCK(CBB_0) | BG_SCREENBLOCK(SBB_0) | BG_SIZE(3);
     BG_H_SCROLL_0 = 0;
     BG_V_SCROLL_0 = 0;
 
+    // (1) create the tiles: basic tile and a cross
+    const Tile tiles[2] = {
+        {{0x11111111, 0x01111111, 0x01111111, 0x01111111,
+          0x01111111, 0x01111111, 0x01111111, 0x00000001}},
+        {{0x00000000, 0x00100100, 0x01100110, 0x00011000,
+          0x00011000, 0x01100110, 0x00100100, 0x00000000}},
+    };
+    TILE_MEM[CBB_0][0] = tiles[0];
+    TILE_MEM[CBB_0][1] = tiles[1];
+
+    // (2) create a palette
+    PAL_BANK_BG[0][1] = rgb15(31,  0,  0);
+    PAL_BANK_BG[1][1] = rgb15( 0, 31,  0);
+    PAL_BANK_BG[2][1] = rgb15( 0,  0, 31);
+    PAL_BANK_BG[3][1] = rgb15(16, 16, 16);
+
+    // (3) Create a map: four contingent blocks of
+    //   0x0000, 0x1000, 0x2000, 0x3000.
+    u16 *pse = bg0_map;
+    for(int i = 0; i < 4; i++) {
+        for(int j = 0; j < 32 * 32; j++) {
+            *pse++ = SCREENBLOCK_ENTRY_PAL(i) | 0;
+        }
+    }
+}
+
+int main(void) {
+    init_map();
     // Configure the display in mode 0 to show OBJs, where tile memory is
     // sequential.
     DISP_CTRL = DISP_ENABLE_SPRITES | DISP_MODE_0 | DISP_BG_0;
 
+    u32 tx, ty, se_curr, se_prev= CROSS_TY * 32 + CROSS_TX;
+
+    bg0_map[se_prev]++; // initial position of cross
+
     // Initialize sprite button overlay.
     init_sprite_pal(0, COLOR_WHITE);
     init_sprites(0);
@@ -51,6 +86,15 @@ int main(void) {
         if (key_hold(KEY_RIGHT)) {
             x += 3;
         }
+        tx = ((x >> 3) + CROSS_TX) & 0x3F;
+        ty = ((y >> 3) + CROSS_TY) & 0x3F;
+
+        se_curr = se_index(tx, ty, 64);
+        if(se_curr != se_prev) {
+            bg0_map[se_prev]--;
+            bg0_map[se_curr]++;
+            se_prev= se_curr;
+        }
 
         frame_counter++;
         BG_H_SCROLL_0 = x;