better scrolling

src/main/java/cz/kamma/kfmanager/ui/FilePanelTab.java

@@ -725,9 +725,23 @@ public class FilePanelTab extends JPanel {
                     JScrollBar hBar = sp.getHorizontalScrollBar();
                     if (hBar != null && hBar.isVisible()) {
                         int rotation = e.getWheelRotation();
-                        // Scroll by a larger amount for significantly faster movement
+                        int colWidth = fileTable.getColumnModel().getColumn(0).getPreferredWidth();
-                        int amount = rotation * hBar.getUnitIncrement() * 10;
+                        if (colWidth > 0) {
-                        hBar.setValue(hBar.getValue() + amount);
+                            // Calculate current value and round to nearest column to ensure snapping
+                            int currentVal = hBar.getValue();
+                            int currentCol = (int) Math.round((double) currentVal / colWidth);
+                            
+                            // Scroll by 2 columns per notch for speed but keep it aligned
+                            int nextCol = currentCol + (rotation * 2);
+                            int newVal = nextCol * colWidth;
+                            
+                            // Bounds checking
+                            int maxVal = hBar.getMaximum() - hBar.getVisibleAmount();
+                            if (newVal < 0) newVal = 0;
+                            if (newVal > maxVal) newVal = maxVal;
+                            
+                            hBar.setValue(newVal);
+                        }
                     }
                 }
                 e.consume();
@@ -2706,33 +2720,9 @@ public class FilePanelTab extends JPanel {
         return icon;
     }
 
-    private void updateColumnWidths() {
+    private int calculateCurrentColumnWidth() {
-        if (viewMode == ViewMode.FULL) {
+        if (tableModel.items == null || tableModel.items.isEmpty()) return 0;
-            if (fileTable.getColumnModel().getColumnCount() == 3) {
-                fileTable.getColumnModel().getColumn(0).setPreferredWidth(300);
-                fileTable.getColumnModel().getColumn(1).setPreferredWidth(100);
-                fileTable.getColumnModel().getColumn(2).setPreferredWidth(150);
-            }
-        } else if (viewMode == ViewMode.BRIEF) {
-            int columnCount = tableModel.getColumnCount();
-            if (columnCount == 0) {
-                return;
-            }
         
-            // If ColumnModel has not yet adapted to the new structure (e.g. after fireTableStructureChanged()),
-            // wait and try to set renderers later - otherwise new columns won't get a renderer and icons won't
-            // show up in FULL mode.
-            if (fileTable.getColumnModel().getColumnCount() != columnCount) {
-                SwingUtilities.invokeLater(() -> updateColumnRenderers());
-                return;
-            }
-
-            // Turn off auto-resize so preferred widths are honored and horizontal scrolling appears
-            fileTable.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
-
-            // Compute the preferred column width based on the longest displayed
-            // name in the current directory (include brackets for directories)
-            // plus the widest icon width and some padding.
         java.awt.FontMetrics fm = fileTable.getFontMetrics(fileTable.getFont());
         int maxTextWidth = 0;
         int maxIconWidth = 0;
@@ -2770,11 +2760,59 @@ public class FilePanelTab extends JPanel {
 
         // Add icon width and padding (left/right + gap between icon and text)
         int padding = 36; // reasonable extra space
-            int columnWidth = maxTextWidth + maxIconWidth + padding;
+        return maxTextWidth + maxIconWidth + padding;
+    }
+
+    private void updateColumnWidths() {
+        if (viewMode == ViewMode.FULL) {
+            if (fileTable.getColumnModel().getColumnCount() == 3) {
+                fileTable.getColumnModel().getColumn(0).setPreferredWidth(300);
+                fileTable.getColumnModel().getColumn(1).setPreferredWidth(100);
+                fileTable.getColumnModel().getColumn(2).setPreferredWidth(150);
+            }
+        } else if (viewMode == ViewMode.BRIEF) {
+            int columnCount = tableModel.getColumnCount();
+            if (columnCount == 0) {
+                return;
+            }
+
+            // If ColumnModel has not yet adapted to the new structure (e.g. after fireTableStructureChanged()),
+            // wait and try to set renderers later - otherwise new columns won't get a renderer and icons won't
+            // show up in FULL mode.
+            if (fileTable.getColumnModel().getColumnCount() != columnCount) {
+                SwingUtilities.invokeLater(() -> updateColumnRenderers());
+                return;
+            }
+
+            // Turn off auto-resize so preferred widths are honored and horizontal scrolling appears
+            fileTable.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
+
+            int columnWidth = calculateCurrentColumnWidth();
+            int viewportWidth = fileTable.getParent().getWidth();
 
             for (int i = 0; i < columnCount; i++) {
                 fileTable.getColumnModel().getColumn(i).setPreferredWidth(columnWidth);
             }
+            
+            // Adjust the very last column to make the total table width such that 
+            // the maximum scroll position is a multiple of columnWidth.
+            if (tableModel.extraColumns > 0 && columnWidth > 0 && viewportWidth > 0) {
+                int actualDataWidth = tableModel.briefColumns * columnWidth;
+                int k = (int) Math.ceil((double) (actualDataWidth - viewportWidth) / columnWidth);
+                int targetTotalWidth = k * columnWidth + viewportWidth;
+                
+                int widthOfOthers = (columnCount - 1) * columnWidth;
+                int lastColWidth = targetTotalWidth - widthOfOthers;
+                if (lastColWidth > 0) {
+                    fileTable.getColumnModel().getColumn(columnCount - 1).setPreferredWidth(lastColWidth);
+                }
+            }
+
+            // Ensure horizontal scrollbar snaps to column widths
+            JScrollPane sp = (JScrollPane) SwingUtilities.getAncestorOfClass(JScrollPane.class, fileTable);
+            if (sp != null) {
+                sp.getHorizontalScrollBar().setUnitIncrement(columnWidth);
+            }
         }
     }
     
@@ -3191,6 +3229,7 @@ public class FilePanelTab extends JPanel {
         private List<FileItem> items = new ArrayList<>();
         private String[] columnNames = {"Name", "Size", "Date"};
         public int briefColumns = 1;
+        public int extraColumns = 0;
         public int briefRowsPerColumn = 10;
         
         public void setItems(List<FileItem> items) {
@@ -3211,6 +3250,7 @@ public class FilePanelTab extends JPanel {
         public void calculateBriefLayout() {
             if (items.isEmpty()) {
                 briefColumns = 1;
+                extraColumns = 0;
                 briefRowsPerColumn = 1;
                 return;
             }
@@ -3221,11 +3261,36 @@ public class FilePanelTab extends JPanel {
             if (availableHeight <= 0 || rowHeight <= 0) {
                 briefRowsPerColumn = Math.max(1, items.size());
                 briefColumns = 1;
+                extraColumns = 0;
                 return;
             }
             
             briefRowsPerColumn = Math.max(1, availableHeight / rowHeight);
             briefColumns = (int) Math.ceil((double) items.size() / briefRowsPerColumn);
+            
+            // Calculate extra columns to allow snapping correctly at the end.
+            // We want the scrolling to stop precisely when the last column is fully visible 
+            // on the right, but also ensure the left-most visible column is snapped to the left edge.
+            int colWidth = calculateCurrentColumnWidth();
+            int viewportWidth = fileTable.getParent().getWidth();
+            if (colWidth > 0 && viewportWidth > 0 && briefColumns > 0) {
+                int actualWidth = briefColumns * colWidth;
+                if (actualWidth > viewportWidth) {
+                    // Smallest k such that (k * colWidth + viewportWidth) >= actualWidth
+                    int k = (int) Math.ceil((double) (actualWidth - viewportWidth) / colWidth);
+                    int neededWidth = k * colWidth + viewportWidth;
+                    // How many extra columns of 'colWidth' would it take?
+                    // We'll adjust the last one's width in updateColumnWidths
+                    extraColumns = (int) Math.ceil((double) (neededWidth - actualWidth) / colWidth);
+                    if (extraColumns == 0 && neededWidth > actualWidth) {
+                        extraColumns = 1; // Need at least one to hold the fractional part
+                    }
+                } else {
+                    extraColumns = 0;
+                }
+            } else {
+                extraColumns = 0;
+            }
         }
         
         public FileItem getItemFromBriefLayout(int row, int column) {
@@ -3233,6 +3298,8 @@ public class FilePanelTab extends JPanel {
                 return getItem(row);
             }
             
+            if (column >= briefColumns) return null;
+            
             int index = column * briefRowsPerColumn + row;
             if (index >= 0 && index < items.size()) {
                 return items.get(index);
@@ -3251,7 +3318,7 @@ public class FilePanelTab extends JPanel {
         @Override
         public int getColumnCount() {
             if (viewMode == ViewMode.BRIEF) {
-                return briefColumns;
+                return briefColumns + extraColumns;
             }
             return 3;
         }