[GTK] Prototype SWT.VIRTUAL support for Composite (issue 624)

[vogella]

Summary

Experimental, GTK-only implementation of a virtual (handle-less) Composite, addressing eclipse-platform/eclipse.platform.swt#624.

A Composite created with SWT.VIRTUAL creates no native widget. Its children are parented to the nearest non-virtual ancestor, while the virtual composite continues to act as a layout container. This reduces the number of native controls and the nesting depth of the native widget hierarchy — the motivation in the issue (resize flicker, double-buffering cost, and platform limits on deeply nested controls, e.g. the ~49-level HWND limit on Windows).

Mechanism

• createHandle() skips native widget creation for SWT.VIRTUAL.
• parentingHandle() walks up to the nearest non-virtual ancestor, so children attach to that ancestor's native container.
• _getChildren() filters native children by logical parent and appends Java-tracked virtual children (handle-less children are otherwise invisible to native enumeration and to disposal/reskin walks).
• Geometry is tracked in Java; child layout coordinates are translated by the cumulative virtual-ancestor offset (Control.parentingOffset()), and descendants are shifted / re-laid-out manually since there is no native size-allocate signal.
• Native lifecycle, focus and z-order paths are guarded for the handle-less case.
• checkStyle() clears H_SCROLL/V_SCROLL/BORDER for virtual composites.

Scope & limitations

A virtual composite is intended purely as a layout/grouping node. With no native surface it cannot scroll, draw a border/background, paint, take focus, or receive its own mouse/keyboard events, and it does not clip its children. Reparenting is disabled (isReparentable() == false). Interleaving virtual and non-virtual siblings under the same parent does not preserve strict creation order.

Not yet implemented: setVisible/setEnabled cascade, and the Win32 / Cocoa implementations (where the real HWND-nesting payoff lives). On those platforms the style is currently ignored and the composite behaves as a normal Composite.

Tests

Two new cross-platform tests in Test_org_eclipse_swt_widgets_Composite (test_VIRTUAL_actsAsLayoutContainer, test_VIRTUAL_nested) assert behaviour that holds on GTK (virtual path) and on Win32/Cocoa (style ignored → normal composite).

Status

⚠️ This was developed without a local GTK native build or display, so it has not been compiled or run. It is published to let CI compile it and run the suite. Treat it as a starting point / RFC rather than a finished feature.

🤖 Generated with Claude Code

https://claude.ai/code/session_01SQvhWB835Yq5KUwvXaE4Zb

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Generated by Claude Code

[gemini-code-assist]

Code Review

This pull request introduces experimental support for virtual (SWT.VIRTUAL) composites in SWT GTK. A virtual composite acts as a lightweight, handle-less layout container without creating its own native operating-system control, flattening its children onto the nearest non-virtual ancestor. The changes include tracking virtual geometry, managing virtual children, routing parenting handles, and adjusting coordinate calculations in Control. Additionally, unit tests are added to verify layout and disposal behavior. The reviewer highlighted a critical stability concern where calling native GTK/GDK functions on a virtual composite's null handle could cause JVM crashes or GTK warnings, suggesting overrides for several core methods (such as redraw, visibility, enablement, printing, and coordinate translation) to safely handle the virtual case.

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[gemini-code-assist]

Critical Stability and Correctness Fixes for Virtual Composites

Since a virtual (SWT.VIRTUAL) composite has no native widget (handle == 0), calling native GTK/GDK functions on its handle or window will trigger native GTK critical warnings or crash the JVM.

To ensure stability and correctness, we must override several core Control and Composite methods to safely handle the virtual case:

1. Color & Font Settings (setBackgroundGdkRGBA, setForegroundGdkRGBA, setFontDescription): Prevent passing 0 to GTK style context and CSS provider functions.
2. Redraw & Update (redraw, update): Recursively delegate to the parent composite with translated coordinates instead of querying the non-existent native widget/window.
3. Visibility & Enablement (setVisible, setEnabled): Safely update the internal states and send events without calling native GTK show/hide/realize functions on a null handle.
4. Printing (print, printWidget): Prevent native crashes when printing a parent container that contains virtual composites by recursively printing children.
5. Coordinate Translation (toControl, toDisplay): Safely translate coordinates using the parent's coordinate space instead of calling native window origin/translation functions on a null handle.
6. Layout & Mirroring (getChildrenCount, getClientWidth): Return the correct logical child count and virtual width (crucial for RTL/mirrored coordinate calculations) instead of querying the native widget allocation.

@Override
void setZOrder (Control sibling, boolean above, boolean fixRelations, boolean fixChildren) {
	// A virtual composite has no native widget, so there is no native z-order to change.
	if (isVirtual ()) return;
	super.setZOrder (sibling, above, fixRelations, fixChildren);
}

@Override
void setBackgroundGdkRGBA (GdkRGBA rgba) {
	if (isVirtual ()) return;
	super.setBackgroundGdkRGBA (rgba);
}

@Override
void setForegroundGdkRGBA (GdkRGBA rgba) {
	if (isVirtual ()) return;
	super.setForegroundGdkRGBA (rgba);
}

@Override
void setFontDescription (long font) {
	if (isVirtual ()) return;
	super.setFontDescription (font);
}

@Override
public void redraw (int x, int y, int width, int height, boolean all) {
	checkWidget();
	if (isVirtual ()) {
		parent.redraw (x + virtualX, y + virtualY, width, height, all);
		return;
	}
	super.redraw (x, y, width, height, all);
}

@Override
void redraw (boolean all) {
	checkWidget();
	if (isVirtual ()) {
		parent.redraw (virtualX, virtualY, virtualWidth, virtualHeight, all);
		return;
	}
	super.redraw (all);
}

@Override
void update (boolean all, boolean flush) {
	checkWidget();
	if (isVirtual ()) {
		parent.update (all, flush);
		return;
	}
	super.update (all, flush);
}

@Override
public void setVisible (boolean visible) {
	checkWidget();
	if (isVirtual ()) {
		if (((state & HIDDEN) == 0) == visible) return;
		if (visible) {
			sendEvent (SWT.Show);
			if (isDisposed ()) return;
			state &= ~HIDDEN;
		} else {
			state |= HIDDEN;
			sendEvent (SWT.Hide);
		}
		return;
	}
	super.setVisible (visible);
}

@Override
public void setEnabled (boolean enabled) {
	checkWidget();
	if (isVirtual ()) {
		if (((state & DISABLED) == 0) == enabled) return;
		if (enabled) {
			state &= ~DISABLED;
		} else {
			state |= DISABLED;
		}
		return;
	}
	super.setEnabled (enabled);
}

@Override
public boolean print (GC gc) {
	checkWidget ();
	if (gc == null) error (SWT.ERROR_NULL_ARGUMENT);
	if (gc.isDisposed ()) error (SWT.ERROR_INVALID_ARGUMENT);
	if (isVirtual ()) {
		return false;
	}
	return super.print (gc);
}

@Override
void printWidget (GC gc, long drawable, int depth, int x, int y) {
	if (isVirtual ()) {
		Control [] children = _getChildren ();
		for (int i=children.length-1; i>=0; --i) {
			Control child = children [i];
			if (child.getVisible ()) {
				Point location = child.getLocation ();
				child.printWidget (gc, drawable, depth, x + location.x, y + location.y);
			}
		}
		return;
	}
	super.printWidget (gc, drawable, depth, x, y);
}

@Override
public Point toControl (int x, int y) {
	checkWidget ();
	if (isVirtual ()) {
		Point parentPoint = parent.toControl (x, y);
		return new Point (parentPoint.x - virtualX, parentPoint.y - virtualY);
	}
	return super.toControl (x, y);
}

@Override
public Point toDisplay (int x, int y) {
	checkWidget ();
	if (isVirtual ()) {
		return parent.toDisplay (x + virtualX, y + virtualY);
	}
	return super.toDisplay (x, y);
}

@Override
int getChildrenCount () {
	if (isVirtual ()) {
		return _getChildren ().length;
	}
	return super.getChildrenCount ();
}

@Override
int getClientWidth () {
	if (isVirtual ()) {
		return virtualWidth;
	}
	return super.getClientWidth ();
}

[github-actions]

Test Results

  159 files   -    23    159 suites   - 23   21m 57s ⏱️ - 3m 39s
4 580 tests  -   143  4 360 ✅  -   340  217 💤 +194  0 ❌ ±0  3 🔥 +3 
5 512 runs   - 1 300  5 376 ✅  - 1 273  133 💤  -  30  0 ❌ ±0  3 🔥 +3 

For more details on these errors, see this check.

Results for commit 72a8be4. ± Comparison against base commit 7f9089e.

This pull request removes 145 and adds 2 tests. Note that renamed tests count towards both.

org.eclipse.swt.browser.EdgeTests ‑ handlingOfInvalidFileURIs
org.eclipse.swt.browser.EdgeTests ‑ handlingOfNonFileURIs
org.eclipse.swt.browser.EdgeTests ‑ handlingOfTempDirWithSpacesAndUnicodeCharacters
org.eclipse.swt.browser.EdgeTests ‑ handlingOfUpperLowerCase
org.eclipse.swt.graphics.CursorWin32Tests ‑ testDestroyHandlesExceptPreservesRetainedHandle
org.eclipse.swt.graphics.CursorWin32Tests ‑ testDisposedCursorReturnsZeroHandle
org.eclipse.swt.graphics.CursorWin32Tests ‑ testHandleIsCachedForSameZoomLevel
org.eclipse.swt.graphics.CursorWin32Tests ‑ testImageDataCursorProducesDifferentHandlesForDifferentZoomLevels
org.eclipse.swt.graphics.GCWin32Tests ‑ drawnElementsShouldScaleUpToTheRightZoomLevel
org.eclipse.swt.graphics.GCWin32Tests ‑ gcZoomLevelMustChangeOnShellZoomChange
…

org.eclipse.swt.tests.junit.Test_org_eclipse_swt_widgets_Composite_Virtual ‑ test_VIRTUAL_actsAsLayoutContainer
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_widgets_Composite_Virtual ‑ test_VIRTUAL_nested

This pull request skips 198 tests.

org.eclipse.swt.tests.junit.Test_org_eclipse_swt_browser_Browser ‑ test_BrowserFunction_availableBeforePageScripts_issue20
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_browser_Browser ‑ test_BrowserFunction_availableOnLoad_concurrentInstances_issue20
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_browser_Browser ‑ test_Constructor_multipleInstantiationsInDifferentThreads
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_browser_Browser_IE ‑ test_BrowserFunction_callback
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_browser_Browser_IE ‑ test_BrowserFunction_callback_afterPageReload
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_browser_Browser_IE ‑ test_BrowserFunction_callback_stackedCalls
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_browser_Browser_IE ‑ test_BrowserFunction_callback_with_String
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_browser_Browser_IE ‑ test_BrowserFunction_callback_with_boolean
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_browser_Browser_IE ‑ test_BrowserFunction_callback_with_integer
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_browser_Browser_IE ‑ test_BrowserFunction_callback_with_javaReturningInt
…

♻️ This comment has been updated with latest results.