add simple sound output, noise when shooting. traveltime of objects is now independent of speed.

src/main.c

 #include "maps.h"
 #include "obj.h"
 #include "sprites.h"
+#include "sound.h"
 
 // The metasprite will be built starting with hardware sprite zero (the first)
 #define SPR_NUM_START 0
 
     spr_init();
     obj_init();
+    snd_init();
 
     SHOW_SPRITES;
     SPRITES_8x8;
         }
 
         if (KEY_PRESSED(J_B)) {
+            int8_t ret = -1;
             switch (rot) {
                 case ROT_0:
-                    obj_add(SPR_SHOT, 0, -SHIP_OFF, 0, -SHOT_SPEED);
+                    ret = obj_add(SPR_SHOT, 0, -SHIP_OFF, SpdX, SpdY - SHOT_SPEED);
                 break;
 
                 case ROT_90:
-                    obj_add(SPR_SHOT, SHIP_OFF, 0, SHOT_SPEED, 0);
+                    ret = obj_add(SPR_SHOT, SHIP_OFF, 0, SpdX + SHOT_SPEED, SpdY);
                 break;
 
                 case ROT_180:
-                    obj_add(SPR_SHOT, 0, SHIP_OFF, 0, SHOT_SPEED);
+                    ret = obj_add(SPR_SHOT, 0, SHIP_OFF, SpdX, SpdY + SHOT_SPEED);
                 break;
 
                 case ROT_270:
-                    obj_add(SPR_SHOT, -SHIP_OFF, 0, -SHOT_SPEED, 0);
+                    ret = obj_add(SPR_SHOT, -SHIP_OFF, 0, SpdX - SHOT_SPEED, SpdY);
                 break;
 
                 default:
                     break;
             }
+
+            if (ret == OBJ_ADDED) {
+                snd_noise();
+            }
         }
 
         PosX += SpdX;

src/obj.c

 #include "sprites.h"
 
 #define MAX_OBJ 10
-#define MAX_TRAVEL 2000
+#define MAX_TRAVEL 250
 
 struct obj {
     uint8_t active;
     int16_t off_y;
     int16_t spd_x;
     int16_t spd_y;
-    uint16_t travel;
+    uint8_t travel;
 };
 
 static struct obj objs[MAX_OBJ];
         objs[i].off_x += objs[i].spd_x - spd_x;
         objs[i].off_y += objs[i].spd_y - spd_y;
 
-        objs[i].travel += abs(objs[i].spd_x) + abs(objs[i].spd_y);
+        objs[i].travel += 1;
         if (objs[i].travel >= MAX_TRAVEL) {
             objs[i].active = 0;
         }

src/sound.c

+/*
+ * sound.c
+ * Duality
+ *
+ * Copyright (C) 2025 Thomas Buck <thomas@xythobuz.de>
+ *
+ * Based on examples from gbdk-2020:
+ * https://github.com/gbdk-2020/gbdk-2020/blob/develop/gbdk-lib/examples/cross-platform/metasprites/src/metasprites.c
+ * https://github.com/gbdk-2020/gbdk-2020/blob/develop/gbdk-lib/examples/gb/galaxy/galaxy.c
+ * https://github.com/gbdk-2020/gbdk-2020/blob/develop/gbdk-lib/examples/gb/rand/rand.c
+ */
+
+#include <gbdk/platform.h>
+
+#include "sound.h"
+
+void snd_init(void) {
+    NR52_REG = 0x80; // sound on
+    NR51_REG = 0xFF; // all channels on left and right
+
+#ifdef DEBUG
+    NR50_REG = 0x33; // left and right on half volume
+#else
+    NR50_REG = 0x77; // left and right on full volume
+#endif
+}
+
+void snd_noise(void) {
+    NR41_REG = 0x2F; // length timer, higher value is shorter time (up to 0x3F)
+    NR42_REG = 0xF0; // initially full volume, no volume changes over time
+    NR43_REG = 0x11; // frequency distribution
+    NR44_REG = 0xC0; // trigger and enable length
+}

src/sound.h

+/*
+ * sound.h
+ * Duality
+ *
+ * Copyright (C) 2025 Thomas Buck <thomas@xythobuz.de>
+ *
+ * Based on examples from gbdk-2020:
+ * https://github.com/gbdk-2020/gbdk-2020/blob/develop/gbdk-lib/examples/cross-platform/metasprites/src/metasprites.c
+ * https://github.com/gbdk-2020/gbdk-2020/blob/develop/gbdk-lib/examples/gb/galaxy/galaxy.c
+ * https://github.com/gbdk-2020/gbdk-2020/blob/develop/gbdk-lib/examples/gb/rand/rand.c
+ */
+
+#ifndef __SOUND_H__
+#define __SOUND_H__
+
+void snd_init(void);
+void snd_noise(void);
+
+#endif // __SOUND_H__