iOS: add optional haptic feedback for touch-control press edges

dm/games/settings.tsv

@@ -12,3 +12,4 @@ DM_OPMODE	choice	1=Docked,0=Handheld	DM_GAME_OPMODE	always	Console mode
 DM_LANG	choice	languages	build:DM_LANG	languages>1	Game language
 DM_SHOW_FPS	toggle	-	build:DM_SHOW_FPS	always	Frame-rate counter
 DM_METAL_HUD	toggle	-	0	always	Performance HUD
+DM_TOUCH_HAPTICS	toggle	-	1	always	Touch feedback	Haptic clicks when pressing touch controls.

dm/ios/Sources/DmGamepad.m

@@ -105,6 +105,8 @@ static __weak DmGamepad *g_view;
     CAShapeLayer *_key[B_N]; CATextLayer *_label[B_N];   // one layer per key
     CAShapeLayer *_ring, *_knob;                   // the left stick (the right one is not drawn)
     CAShapeLayer *_swap; CATextLayer *_swapLabel; BOOL _swapHeld;
+    UIImpactFeedbackGenerator *_touchFeedback;       // one short feedback per touch-control press edge
+    unsigned _hapticSticks;
     BOOL _stickShown;                              // the left stick was held at the last refresh
     BOOL _full, _tap;                              // the 3D layout / the Tap layout is current
     CALayer *_controls;                            // holds every control layer: hidden while a physical controller is connected (the view itself stays, for game touches)
@@ -129,6 +131,11 @@ static BOOL fullOnly(int b) { return b == B_LS || b == B_RS || b >= B_LEFT; }
 - (instancetype)initWithFrame:(CGRect)f {
     if ((self = [super initWithFrame:f])) {
         self.multipleTouchEnabled = YES; self.opaque = NO; self.backgroundColor = UIColor.clearColor;
+        const char *feedback = getenv("DM_TOUCH_HAPTICS");
+        if (!feedback || atoi(feedback)) {
+            _touchFeedback = [[UIImpactFeedbackGenerator alloc] initWithStyle:UIImpactFeedbackStyleLight];
+            [_touchFeedback prepare];
+        }
         _owner = [NSMapTable strongToStrongObjectsMapTable]; _faceOf = [NSMapTable strongToStrongObjectsMapTable];
         static dispatch_once_t once;
         dispatch_once(&once, ^{
@@ -252,6 +259,12 @@ static CGFloat dist(CGPoint a, CGPoint b) { return hypot(a.x - b.x, a.y - b.y);
         ax[i * 2] = (int32_t)lrint(o.x * m * 32767); ax[i * 2 + 1] = (int32_t)lrint(-o.y * m * 32767);   // host: up is positive; rounded so full tilt is exactly 32767
     }
     BOOL changed = face != _faceBits || dpad != _dpadBits || btn != _btnBits || swap != _swapHeld;
+    uint64_t pressed = (face | dpad | btn) & ~(_faceBits | _dpadBits | _btnBits);
+    unsigned gripping = (_stick[0] ? 1u : 0) | (_stick[1] ? 2u : 0);
+    if (pressed || (swap && !_swapHeld) || (gripping & ~_hapticSticks)) {
+        [_touchFeedback impactOccurredWithIntensity:0.6]; [_touchFeedback prepare];
+    }
+    _hapticSticks = gripping;
     _faceBits = face; _dpadBits = dpad; _btnBits = btn; _swapHeld = swap;
     pthread_mutex_lock(&g_mu);
     g_touch_btn = face | dpad | btn; g_touch_lx = ax[0]; g_touch_ly = ax[1]; g_touch_rx = ax[2]; g_touch_ry = ax[3];