Stabilize automatic tile layouts

kwin/scripts/shift-tiling/contents/ui/main.qml

@@ -7,9 +7,10 @@
 //   - One persistent layout tree per output, keyed by output.name
 //   - Tree nodes are split groups or window leaves; leaf rects are absolute
 //     in-screen coordinates
-//   - On add/remove/reorder the tree is updated and then laid out for the
-//     affected screen, preserving the split structure instead of rebuilding a
-//     fresh linear BSP from window count
+//   - Automatic add/remove rebuilds a stable master-stack tree from window
+//     order, so normal app churn does not leave arbitrary nested splits behind
+//   - Explicit drag insertion still edits the tree directly because that is a
+//     deliberate user layout change
 //   - Drag detection uses interactiveMoveResizeStarted/Stepped/Finished
 //   - Dragging over a tile shows the exact directional split that will be
 //     created on drop
@@ -25,6 +26,7 @@ Item {
     // ── Configuration ───────────────────────────────────────────────────────
     readonly property int outerGap: 8
     readonly property int innerGap: 8    // half applied to each edge → 4px per tile
+    readonly property real stablePrimaryRatio: 0.58
 
     // ── State ───────────────────────────────────────────────────────────────
 
@@ -258,6 +260,70 @@ Item {
         return lastLeafKey(node.second) || lastLeafKey(node.first);
     }
 
+    function orderedWindowsForScreen(outputName) {
+        const windows = [];
+        const seen = {};
+        const leaves = [];
+        collectLeaves(screenLayouts[outputName], leaves);
+
+        for (let i = 0; i < leaves.length; i++) {
+            const win = leaves[i].win;
+            const key = windowKey(win);
+            if (!key || seen[key] || !isTileable(win)) continue;
+            if (!win.output || win.output.name !== outputName) continue;
+            seen[key] = true;
+            windows.push(win);
+        }
+
+        return windows;
+    }
+
+    function appendWindowIfMissing(windows, win) {
+        const key = windowKey(win);
+        if (!key) return false;
+
+        for (let i = 0; i < windows.length; i++) {
+            if (windowKey(windows[i]) === key) {
+                return false;
+            }
+        }
+
+        windows.push(win);
+        return true;
+    }
+
+    function buildStableStack(windows, startIndex) {
+        const remaining = windows.length - startIndex;
+        if (remaining <= 0) return null;
+        if (remaining === 1) return makeLeaf(windows[startIndex]);
+
+        return makeSplit(
+            "horizontal",
+            makeLeaf(windows[startIndex]),
+            buildStableStack(windows, startIndex + 1),
+            1 / remaining
+        );
+    }
+
+    function buildStableLayout(windows) {
+        if (!windows || windows.length === 0) return null;
+        if (windows.length === 1) return makeLeaf(windows[0]);
+        if (windows.length === 2) {
+            return makeSplit("vertical", makeLeaf(windows[0]), makeLeaf(windows[1]), 0.5);
+        }
+
+        return makeSplit(
+            "vertical",
+            makeLeaf(windows[0]),
+            buildStableStack(windows, 1),
+            stablePrimaryRatio
+        );
+    }
+
+    function setStableLayout(outputName, windows) {
+        setScreenLayout(outputName, buildStableLayout(windows));
+    }
+
     function containsLeaf(node, key) {
         if (!node || !key) return false;
         if (node.kind === "leaf") return windowKey(node.win) === key;
@@ -325,24 +391,9 @@ Item {
     }
 
     function insertWindowInLayout(outputName, win) {
-        const rootNode = screenLayouts[outputName];
-        const newLeaf = makeLeaf(win);
-
-        if (!rootNode) {
-            setScreenLayout(outputName, newLeaf);
-            return;
-        }
-
-        let targetKey = "";
-        const active = KWinComponents.Workspace.activeWindow;
-        if (active && active.output && active.output.name === outputName && windowKey(active) !== windowKey(win)) {
-            targetKey = windowKey(active);
-        }
-        if (!containsLeaf(rootNode, targetKey)) {
-            targetKey = lastLeafKey(rootNode);
-        }
-
-        setScreenLayout(outputName, splitLeaf(rootNode, targetKey, newLeaf, "", workRect(win)));
+        const windows = orderedWindowsForScreen(outputName);
+        if (!appendWindowIfMissing(windows, win)) return;
+        setStableLayout(outputName, windows);
     }
 
     function removeWindowFromLayout(outputName, win) {
@@ -350,9 +401,28 @@ Item {
         const rootNode = screenLayouts[outputName];
         if (!key || !rootNode) return false;
 
-        const result = removeLeaf(rootNode, key);
-        if (!result.leaf) return false;
-        setScreenLayout(outputName, result.node);
+        const leaves = [];
+        const seen = {};
+        const remaining = [];
+        let removed = false;
+        collectLeaves(rootNode, leaves);
+
+        for (let i = 0; i < leaves.length; i++) {
+            const leafWindow = leaves[i].win;
+            const leafKey = windowKey(leafWindow);
+            if (leafKey === key) {
+                removed = true;
+                continue;
+            }
+
+            if (!leafKey || seen[leafKey] || !isTileable(leafWindow)) continue;
+            if (!leafWindow.output || leafWindow.output.name !== outputName) continue;
+            seen[leafKey] = true;
+            remaining.push(leafWindow);
+        }
+
+        if (!removed) return false;
+        setStableLayout(outputName, remaining);
         return true;
     }
 

tests/check-dynamic-tiles-motion.sh

@@ -54,6 +54,16 @@ require_line "$effect_qml" "showPreview(\"insert\""
 require_line "$effect_qml" "showPreview(\"float\""
 require_line "$effect_qml" "showPreview(\"restore\""
 
+require_line "$tiling_script" "readonly property real stablePrimaryRatio: 0.58"
+require_line "$tiling_script" "function orderedWindowsForScreen(outputName)"
+require_line "$tiling_script" "function buildStableStack(windows, startIndex)"
+require_line "$tiling_script" "function buildStableLayout(windows)"
+require_line "$tiling_script" "function setStableLayout(outputName, windows)"
+require_line "$tiling_script" "setStableLayout(outputName, windows)"
+require_line "$tiling_script" "setStableLayout(outputName, remaining)"
+
+reject_line "$tiling_script" "targetKey = lastLeafKey(rootNode)"
+reject_line "$tiling_script" "setScreenLayout(outputName, splitLeaf(rootNode, targetKey"
 reject_line "$tiling_script" "KWinComponents.Workspace.showOutline(dragOutlineRect)"
 reject_line "$tiling_script" "KWinComponents.Workspace.hideOutline()"