Added alpha blending

src/main.cpp

@@ -118,6 +118,17 @@ void update_graphics() {
             bg1map[x + y32] = tile | (PAL_GRADIENT << 12);
     }
 
+    // Enable alpha blending of background 1.
+    // My guess: BLEND_DST_BACKDROP is the 14th bit at 1, BLEND_SRC_BG1 is the
+    //           2nd bit at 1 and BLEND_ALPHA are bits 8th and 7th at 10.
+    //           BLEND_DST_BACKDROP 0010000000000000
+    //           BLEND_SRC_BG1      0000000000000010
+    //           BLEND_ALPHA        0000000010000000
+    //           -----------------------------------
+    //                              0010000010000010
+    REG_BLDCNT = BLEND_ALPHA | BLEND_SRC_BG1 | BLEND_DST_BACKDROP;
+    REG_BLDALPHA = (4) + (16 << 8);  // This is computed at compile time.
+
     videoSetMode(MODE_0_2D | DISPLAY_BG0_ACTIVE | DISPLAY_BG1_ACTIVE);
 }