fix(gamescope): direct-touch drags work again in games that confine a hidden cursor

tools/gamescope/PATCHES.md

@@ -302,6 +302,7 @@ For games that confine a visible cursor and warp it, which the automatic rule ca
 The rule only counted a lock with a cursor position hint. A game that hides the cursor and confines the
 pointer through a grab (Wine's ClipCursor) has a constraint with no hint, so the nested pointer stayed
 absolute, the constraint held the X pointer still and no raw motion was produced: the camera froze.
+0133 narrows this, and the upstream hint rule, to games that hold the X pointer.
 
 ## 0129 steamcompmgr, wayland: release a pointer lock at the game's pointer
 
@@ -331,3 +332,15 @@ With `--follow-game-window-mode`, the outer window of a nested SDL gamescope fol
 asking for `_NET_WM_STATE_FULLSCREEN`, or a Steam game covering the X screen without minimise or maximise functions or
 decorations in `_MOTIF_WM_HINTS`, makes the outer window fullscreen on the desktop. Anything else makes it a normal window of the
 game window's size, or a maximised one when that size does not fit the desktop with its title bar and panel. A change is applied only when the wanted mode changes, so a manual resize or Super+F stays.
+
+## 0133 steamcompmgr, wlserver: a pointer constraint is relative only while the game holds the X pointer
+
+A game that hides the system cursor, draws its own and grabs the pointer to its window (Stardew Valley, Balatro) gets a lock
+from Xwayland, which emulates the game's warps with a cursor position hint. Upstream kept any hinted lock relative and 0128
+added every other constraint, so gamescope held the host's pointer lock and DroidDeck turned every direct touch swipe into
+camera motion: dragging in those games only moved their cursor. Without relative mode such a lock still follows gamescope's
+relative motion and touches still place the pointer. gamescope now compares the motion it sends (seat movement, or relative
+motion while the seat is locked) with how the X pointer moves. A hinted constraint starts relative, as upstream, also when its hint arrives with the game's first warp, and is released
+after 30 moving frames on which the X pointer follows. Any constraint goes relative once the X pointer moves less than a quarter
+of that motion on three frames within half a second, as it does when the game recentres it or clips it to a small rectangle
+(PEAK). `tools/tests/test_gamescope_pointer_hold.py` compiles the rule from this patch.

tools/gamescope/patches/0133-constraint-relative-when-held.patch

@@ -0,0 +1,161 @@
+diff --git a/src/steamcompmgr.cpp b/src/steamcompmgr.cpp
+--- a/src/steamcompmgr.cpp
++++ b/src/steamcompmgr.cpp
+@@ -3165,6 +3165,116 @@
+ 	wlserver_unlock();
+ }
+
++struct PointerHold
++{
++	int nAwayFrames = 0;
++	int nFreeFrames = 0;
++	uint64_t ulFirstAway = 0;
++	bool bHeld = false;
++};
++
++static bool pointer_hold_step( PointerHold &state, bool bConstrained, double flSeatDX, double flSeatDY, double flPointerDX, double flPointerDY, uint64_t ulNow )
++{
++	if ( !bConstrained )
++	{
++		state = PointerHold{};
++		return false;
++	}
++
++	const double flSeat = std::max( std::abs( flSeatDX ), std::abs( flSeatDY ) );
++	if ( flSeat < 4.0 )
++		return state.bHeld;
++
++	const double flMiss = std::max( std::abs( flSeatDX - flPointerDX ), std::abs( flSeatDY - flPointerDY ) );
++	if ( flMiss > flSeat * 0.75 )
++	{
++		if ( state.nAwayFrames == 0 || ulNow - state.ulFirstAway > 500'000'000ul )
++		{
++			state.nAwayFrames = 0;
++			state.ulFirstAway = ulNow;
++		}
++		state.nFreeFrames = 0;
++		if ( ++state.nAwayFrames >= 3 )
++			state.bHeld = true;
++	}
++	else if ( state.bHeld && ++state.nFreeFrames >= 30 )
++	{
++		state = PointerHold{};
++	}
++
++	return state.bHeld;
++}
++
++static bool s_bPointerHeld = false;
++
++static void update_pointer_hold( global_focus_t *pFocus, bool bConstrained, bool bHinted )
++{
++	static PointerHold s_Hold;
++	static bool s_bTracking = false;
++	static double s_flSeatX = 0.0;
++	static double s_flSeatY = 0.0;
++	static int s_nRootX = 0;
++	static int s_nRootY = 0;
++	static bool s_bHinted = false;
++
++	wlserver_lock();
++	const double flX = wlserver.mouse_surface_cursorx;
++	const double flY = wlserver.mouse_surface_cursory;
++	const double flSentX = wlserver.flSentDX;
++	const double flSentY = wlserver.flSentDY;
++	wlserver.flSentDX = 0.0;
++	wlserver.flSentDY = 0.0;
++	wlserver_unlock();
++
++	if ( !bConstrained || !pFocus->cursor )
++	{
++		s_bTracking = false;
++		s_bHinted = false;
++		s_bPointerHeld = pointer_hold_step( s_Hold, false, 0.0, 0.0, 0.0, 0.0, 0 );
++		return;
++	}
++
++	if ( s_bTracking && bHinted && !s_bHinted )
++	{
++		s_Hold = PointerHold{};
++		s_Hold.bHeld = true;
++		s_bPointerHeld = true;
++	}
++	s_bHinted = bHinted;
++
++	double flDX = flX - s_flSeatX;
++	double flDY = flY - s_flSeatY;
++	if ( flDX == 0.0 && flDY == 0.0 )
++	{
++		flDX = flSentX;
++		flDY = flSentY;
++	}
++
++	if ( s_bTracking && flDX == 0.0 && flDY == 0.0 )
++		return;
++
++	int nRootX = 0;
++	int nRootY = 0;
++	pFocus->cursor->QueryRootPosition( &nRootX, &nRootY );
++
++	if ( s_bTracking )
++	{
++		s_bPointerHeld = pointer_hold_step( s_Hold, true, flDX, flDY, nRootX - s_nRootX, nRootY - s_nRootY, get_time_in_nanos() );
++	}
++	else
++	{
++		s_Hold = PointerHold{};
++		s_Hold.bHeld = bHinted;
++		s_bPointerHeld = bHinted;
++	}
++
++	s_bTracking = true;
++	s_flSeatX = flX;
++	s_flSeatY = flY;
++	s_nRootX = nRootX;
++	s_nRootY = nRootY;
++}
++
+ bool ShouldDrawCursor()
+ {
+ 	if ( relative_mouse_forced() )
+@@ -11029,9 +11139,15 @@
+ 						nRelativeMouse != 2 && !bExcludedAppId && !bHasPointerConstraint && !window_is_steam( pPaintFocus->inputFocusWindow ) );
+ 				}
+
++				if ( vblank )
++					update_pointer_hold( pPaintFocus, bHasPointerConstraint && bImageEmpty && nRelativeMouse != 2 && !bExcludedAppId,
++						pPaintFocus->cursor && pPaintFocus->cursor->IsConstrained() );
++
++				const bool bGameHoldsPointer = bHasPointerConstraint && s_bPointerHeld;
++
+ 				const bool bRelativeMouseMode = nRelativeMouse == 2
+ 					? false
+-					: ( bForcedRelativeMouse || s_bFollowClientPointer || ( bImageEmpty && bHasPointerConstraint && !bExcludedAppId ) );
++					: ( bForcedRelativeMouse || s_bFollowClientPointer || ( bImageEmpty && bGameHoldsPointer && !bExcludedAppId ) );
+
+ 				static bool s_bRelativeMouseMode = false;
+ 				if ( s_bRelativeMouseMode && !bRelativeMouseMode && pPaintFocus->cursor &&
+diff --git a/src/wlserver.cpp b/src/wlserver.cpp
+--- a/src/wlserver.cpp
++++ b/src/wlserver.cpp
+@@ -346,6 +346,8 @@
+ {
+ 	assert( wlserver_is_lock_held() );
+
++	wlserver.flSentDX += unaccel_dx;
++	wlserver.flSentDY += unaccel_dy;
+ 	wlr_relative_pointer_manager_v1_send_relative_motion( wlserver.relative_pointer_manager, wlserver.wlr.seat, 0, unaccel_dx, unaccel_dy, unaccel_dx, unaccel_dy );
+ }
+
+diff --git a/src/wlserver.hpp b/src/wlserver.hpp
+--- a/src/wlserver.hpp
++++ b/src/wlserver.hpp
+@@ -171,6 +171,8 @@
+ 	bool bFollowClientPointer = false;
+ 	double flFollowDX = 0.0;
+ 	double flFollowDY = 0.0;
++	double flSentDX = 0.0;
++	double flSentDY = 0.0;
+
+ 	bool button_held[ WLSERVER_BUTTON_COUNT ];
+ 	std::set <uint32_t> touch_down_ids;

tools/tests/test_gamescope_pointer_hold.py

@@ -0,0 +1,137 @@
+from pathlib import Path
+import shutil
+import subprocess
+import tempfile
+import unittest
+
+
+ROOT = Path(__file__).resolve().parents[2]
+PATCH = ROOT / "tools/gamescope/patches/0133-constraint-relative-when-held.patch"
+
+
+def added_source():
+    return "\n".join(line[1:] for line in PATCH.read_text().splitlines() if line.startswith("+") and not line.startswith("+++"))
+
+
+def block(text, start):
+    begin = text.index(start)
+    return text[begin:text.index("\n}", begin) + 3]
+
+
+def rules():
+    text = added_source()
+    return "\n".join([
+        block(text, "struct PointerHold"),
+        block(text, "static bool pointer_hold_step"),
+    ])
+
+
+PREAMBLE = r'''
+#include <algorithm>
+#include <cassert>
+#include <cmath>
+#include <cstdint>
+#include <cstdio>
+'''
+
+MAIN = r'''
+static const uint64_t FRAME = 16'666'667ul;
+
+static bool run(PointerHold &state, int frames, double seatDX, double seatDY, double pointerDX, double pointerDY, uint64_t &now, bool constrained = true) {
+    bool held = state.bHeld;
+    for (int i = 0; i < frames; i++) {
+        now += FRAME;
+        held = pointer_hold_step(state, constrained, seatDX, seatDY, pointerDX, pointerDY, now);
+    }
+    return held;
+}
+
+int main() {
+    uint64_t now = 1'000'000'000ul;
+
+    PointerHold cursorGame;
+    assert(!run(cursorGame, 600, 12.0, -9.0, 12.0, -9.0, now));
+    assert(!run(cursorGame, 600, 40.0, 3.0, 39.0, 3.0, now));
+    assert(!run(cursorGame, 1, 30.0, 0.0, 0.0, 0.0, now));
+    assert(!run(cursorGame, 1, 30.0, 0.0, 30.0, 0.0, now));
+    assert(!run(cursorGame, 1, 30.0, 0.0, 0.0, 0.0, now));
+    assert(!run(cursorGame, 120, 2.0, 1.0, 0.0, 0.0, now));
+
+    PointerHold offset;
+    assert(!run(offset, 600, 25.0, 25.0, 25.0, 25.0, now));
+
+    PointerHold recentring;
+    assert(!run(recentring, 2, -40.0, 12.0, 0.0, 0.0, now));
+    assert(run(recentring, 1, -40.0, 12.0, 1.0, 0.0, now));
+    assert(run(recentring, 600, 0.0, 0.0, 0.0, 0.0, now));
+    assert(run(recentring, 29, 10.0, 4.0, 10.0, 4.0, now));
+    assert(run(recentring, 1, 20.0, 0.0, 0.0, 0.0, now));
+    assert(run(recentring, 29, 10.0, 4.0, 10.0, 4.0, now));
+    assert(!run(recentring, 1, 10.0, 4.0, 10.0, 4.0, now));
+
+    PointerHold clipped;
+    assert(run(clipped, 3, 0.0, 30.0, 0.0, 2.0, now));
+
+    PointerHold spaced;
+    for (int i = 0; i < 10; i++) {
+        assert(!run(spaced, 1, 50.0, 0.0, 0.0, 0.0, now));
+        now += 600'000'000ul;
+    }
+
+    PointerHold hinted;
+    hinted.bHeld = true;
+    assert(run(hinted, 29, 0.0, 15.0, 0.0, 15.0, now));
+    assert(!run(hinted, 1, 0.0, 15.0, 0.0, 15.0, now));
+
+    PointerHold hintedCamera;
+    hintedCamera.bHeld = true;
+    assert(run(hintedCamera, 600, 30.0, -8.0, 0.0, 0.0, now));
+
+    PointerHold chained;
+    for (int i = 0; i < 6; i++) {
+        assert(!run(chained, 1, 50.0, 0.0, 0.0, 0.0, now));
+        now += 400'000'000ul;
+    }
+
+    PointerHold released;
+    assert(run(released, 3, 0.0, -25.0, 0.0, 0.0, now));
+    assert(!run(released, 1, 0.0, -25.0, 0.0, 0.0, now, false));
+    assert(!run(released, 2, 0.0, -25.0, 0.0, 0.0, now));
+
+    puts("ok");
+    return 0;
+}
+'''
+
+
+@unittest.skipUnless(shutil.which("c++"), "needs a C++ compiler")
+class PointerHoldTest(unittest.TestCase):
+    def test_only_a_game_that_holds_the_x_pointer_goes_relative(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            source = Path(tmp) / "hold.cpp"
+            binary = Path(tmp) / "hold"
+            source.write_text(PREAMBLE + rules() + MAIN)
+            subprocess.run(["c++", "-std=c++17", "-Wall", "-Wextra", "-Werror", str(source), "-o", str(binary)], check=True)
+            self.assertEqual(subprocess.run([str(binary)], capture_output=True, text=True, check=True).stdout.strip(), "ok")
+
+    def test_a_hinted_constraint_starts_relative_and_others_wait_for_the_hold(self):
+        added = [line.strip() for line in added_source().splitlines()]
+        self.assertIn("update_pointer_hold( pPaintFocus, bHasPointerConstraint && bImageEmpty && nRelativeMouse != 2 && !bExcludedAppId,", added)
+        self.assertIn("pPaintFocus->cursor && pPaintFocus->cursor->IsConstrained() );", added)
+        self.assertIn("s_Hold.bHeld = bHinted;", added)
+        self.assertIn("if ( s_bTracking && bHinted && !s_bHinted )", added)
+        self.assertIn("const bool bGameHoldsPointer = bHasPointerConstraint && s_bPointerHeld;", added)
+        self.assertIn(": ( bForcedRelativeMouse || s_bFollowClientPointer || ( bImageEmpty && bGameHoldsPointer && !bExcludedAppId ) );", added)
+
+    def test_the_motion_sent_to_clients_is_counted(self):
+        added = [line.strip() for line in added_source().splitlines()]
+        self.assertIn("wlserver.flSentDX += unaccel_dx;", added)
+        self.assertIn("wlserver.flSentDY += unaccel_dy;", added)
+
+    def test_the_forced_and_follow_rules_are_unchanged(self):
+        removed = [line[1:].strip() for line in PATCH.read_text().splitlines() if line.startswith("-") and not line.startswith("---")]
+        self.assertEqual(removed, [": ( bForcedRelativeMouse || s_bFollowClientPointer || ( bImageEmpty && bHasPointerConstraint && !bExcludedAppId ) );"])
+
+
+if __name__ == "__main__":
+    unittest.main()