Make the scrolling container reach the last row of a multi-column grid

[rubensworks]

ScrollingInventoryContainer supports multiple columns — onScroll walks i * getColumns() + j and getScrollStepSize() defaults to getColumns() — but two places still assume there is only one.

The last row is unreachable

ContainerScreenScrolling computes the scrollbar's total rows as filteredItemCount / getColumns(), in both init and updateSearch. That truncates, so WidgetScrollBar#getScrollStep (totalRows - visibleRows) comes out one short and the last, partially filled row can never be scrolled to.

Measured live in a dev client, on a 9-column grid of 985 elements with 6 visible rows, by setting the scrollbar to each value and scrolling fully to the bottom:

totalRows	last row at full scroll	highest reachable element
985 / 9 = 109 (today)	9 cells — a full row	index 980
ceil(985 / 9) = 110 (this PR)	4 cells	past index 984

The final element is index 984, so 981–984 are unreachable: the scrollbar is already at the bottom and they never appear.

Rounded up now, in one getTotalRows() both call sites share, so a subclass that wants different behaviour has a single place to override.

isElementVisible returns false past the first row

public boolean isElementVisible(int row) {
    return row < getPageSize() && getVisibleElement(row) != null;
}

getPageSize() is the number of rows, while the parameter indexes into the visible elements, which number rows × columns. So for a grid this returns false for everything after the first row, even though getVisibleElement returns those elements and onScroll fills them in. It now guards against getPageSize() * getColumns(); for a single-column container the two are identical, so nothing changes for existing users.

A cosmetic third one

The constructor null-filled only the first getPageSize() entries of a list that is rows × columns long. Harmless, since Arrays.asList(new Object[n]) is already all-null, but it read as if the rest were left uninitialized.

How this came up

Building a 9 × 6 recipe grid on ScrollingInventoryContainer in IntegratedCrafting (CyclopsMC/IntegratedCrafting#221). Both were worked around locally there; that workaround can go once a release carries this.

Testing

./gradlew :loader-neoforge:compileJava passes. Behaviour verified in a dev client through the IntegratedCrafting grid, as measured above: with the fix, scrolling fully down lands on a last row holding exactly the 4 remaining elements (985 % 9 = 4), and every cell renders across the whole scroll range.

🤖 Generated with Claude Code

https://claude.ai/code/session_01T9xTc8kXNRDppvXktL24aR

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
5.6% Duplication on New Code

See analysis details on SonarQube Cloud

[coveralls]

coverage: 26.641% (-0.002%) from 26.643% — claude/scrolling-grid-rows into master-1.21-lts