use different implementations of clampScrollX in different scrollers

src/layout/Desktop.ts

@@ -119,12 +119,7 @@ class Desktop {
     }
 
     private clampScrollX(x: number) {
-        let minScroll = 0;
-        let maxScroll = this.grid.getWidth() - this.tilingArea.width;
-        if (maxScroll < 0) {
-            return Math.round(maxScroll / 2);
-        }
-        return clamp(x, minScroll, maxScroll);
+        return this.config.scroller.clampScrollX(this, x);
     }
 
     public setScroll(x: number, force: boolean) {
@@ -233,5 +228,6 @@ namespace Desktop {
 
     export type Scroller = {
         scrollToColumn(desktop: Desktop, column: Column): void;
+        clampScrollX(desktop: Desktop, x: number): number;
     }
 }

src/layout/ScrollerCentered.ts

@@ -2,4 +2,20 @@ class ScrollerCentered {
     public scrollToColumn(desktop: Desktop, column: Column) {
         desktop.scrollCenterRange(column);
     }
+
+    public clampScrollX(desktop: Desktop, x: number) {
+        return ScrollerCentered.clampScrollX(desktop, x);
+    }
+
+    public static clampScrollX(desktop: Desktop, x: number) {
+        const firstColumn = desktop.grid.getFirstColumn();
+        if (firstColumn === null) {
+            return 0;
+        }
+        const lastColumn = desktop.grid.getLastColumn()!;
+
+        let minScroll = Math.round((firstColumn.getWidth() - desktop.tilingArea.width) / 2);
+        let maxScroll = Math.round(desktop.grid.getWidth() - (desktop.tilingArea.width + lastColumn.getWidth()) / 2);
+        return clamp(x, minScroll, maxScroll);
+    }
 }

src/layout/ScrollerGrouped.ts

@@ -12,6 +12,10 @@ class ScrollerGrouped {
         columnRange.addNeighbors(visibleRange, this.layoutConfig.gapsInnerHorizontal, false);
         desktop.scrollCenterRange(columnRange);
     }
+
+    public clampScrollX(desktop: Desktop, x: number) {
+        return ScrollerCentered.clampScrollX(desktop, x);
+    }
 }
 
 namespace ScrollerGrouped {

src/layout/ScrollerLazy.ts

@@ -2,4 +2,13 @@ class ScrollerLazy {
     public scrollToColumn(desktop: Desktop, column: Column) {
         desktop.scrollToRange(column);
     }
+
+    public clampScrollX(desktop: Desktop, x: number) {
+        let minScroll = 0;
+        let maxScroll = desktop.grid.getWidth() - desktop.tilingArea.width;
+        if (maxScroll < 0) {
+            return Math.round(maxScroll / 2);
+        }
+        return clamp(x, minScroll, maxScroll);
+    }
 }