[GTK] Render Tree and Table images crisp at HiDPI zoom

[vogella]

On GTK3 at 200% zoom, images set with TreeItem.setImage or TableItem.setImage were rendered blurry, because GtkCellRendererPixbuf treats the bound pixbuf as a scale 1 image and reduces it to 1x before scaling it up again. Views that paint their images in a PaintItem listener, such as JFace StyledCellLabelProvider based ones, were unaffected, so plain label provider trees like the Mylyn Task List looked noticeably softer than their neighbours. The cell data function now hands the pixbuf renderer the cairo surface already kept in CELL_SURFACE, which carries the device scale, so native cell images are as sharp as GC.drawImage output. Rendering at 100% and on GTK4 is unchanged.

[vogella]

[github-actions]

Test Results (linux)

  109 files  ±0    109 suites  ±0   15m 11s ⏱️ -3s
4 637 tests ±0  4 402 ✅ ±0  235 💤 ±0  0 ❌ ±0 
3 482 runs  ±0  3 393 ✅ ±0   89 💤 ±0  0 ❌ ±0 

Results for commit 4734b80. ± Comparison against base commit 6799800.

[Copilot]

Copilot review overview

🟡 Changes recommended

Reused column model slots retain stale surfaces, causing removed images to reappear.

Review effort: Balanced
Findings: 2

Open (2)

• Clear CELL_SURFACE when destroying TableColumn data · New
• Clear CELL_SURFACE when destroying TreeColumn data · New

What changed in this PR

Uses scale-aware Cairo surfaces to render crisp Tree/Table images on GTK3 HiDPI displays.

Changes:

• Binds GTK3 cell renderers to stored image surfaces.
• Registers pixbuf data callbacks for all Tree/Table renderers.
• Adds the GTK surface property constant.

File	Description
Tree.java	Renders Tree images from Cairo surfaces.
Table.java	Renders Table images from Cairo surfaces.
OS.java	Defines the native surface property name.

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[github-actions]

Test Results

  212 files  ± 0    212 suites  ±0   27m 58s ⏱️ +13s
4 978 tests + 4  4 950 ✅ +4   28 💤 ±0  0 ❌ ±0 
7 233 runs  +12  7 034 ✅ +7  199 💤 +5  0 ❌ ±0 

Results for commit 74ebb77. ± Comparison against base commit 8b89d66.

♻️ This comment has been updated with latest results.

[Copilot]

Copilot review overview

🟡 Changes recommended

Raw surface pointers can become dangling, and GTK4 receives unnecessary per-cell callbacks.

Review effort: Balanced
Findings: 2

Open (2)

• Dangling Cairo surface pointer after disposed image · New
• Dangling Cairo surface pointer after disposed image · New

Resolved since last review (2)

• Clear CELL_SURFACE when destroying TreeColumn data
• Clear CELL_SURFACE when destroying TableColumn data

[Copilot]

Copilot review overview

🟡 Changes recommended

GTK4 receives unnecessary render callbacks, and the painting regressions use zero-sized controls.

Review effort: Balanced
Findings: 2 · 2

Open (4)

• Avoid unconditional GTK4 table cell-data callbacks · New
• Avoid unconditional GTK4 tree cell-data callbacks · New
• Set a nonzero table size to exercise cell painting · New
• Set a nonzero tree size to exercise cell painting · New

Resolved since last review (2)

• Dangling Cairo surface pointer after disposed image
• Dangling Cairo surface pointer after disposed image

[akurtakov]

There are all the details to handle here but it also fixes a nasty drawing problem:

public static void main(String[] args) {
      Display display = new Display();
      Shell shell = new Shell(display);
      shell.setText("zoom " + display.getPrimaryMonitor().getZoom() + "%");
      shell.setLayout(new RowLayout());

      // 1 device pixel black/white stripes at every zoom, any resampling makes it grey
      Image stripes = new Image(display, (ImageDataProvider) zoom -> {
              int size = 16 * zoom / 100;
              ImageData data = new ImageData(size, size, 24, new PaletteData(0xFF0000, 0xFF00, 0xFF));
              for (int y = 0; y < size; y++)
                      for (int x = 0; x < size; x++)
                              data.setPixel(x, y, x % 2 == 0 ? 0 : 0xFFFFFF);
              return data;
      });

      Tree tree = new Tree(shell, SWT.BORDER);
      new TreeItem(tree, SWT.NONE).setImage(stripes);

      Label reference = new Label(shell, SWT.NONE);
      reference.setImage(stripes);

      shell.pack();
      shell.open();
      while (!shell.isDisposed()) {
              if (!display.readAndDispatch()) display.sleep();
      }
      stripes.dispose();
      display.dispose();
}

with GDK_SCALE=2 draws a solid gray instead of striped.

[Copilot]

Copilot review overview

🟢 Approval recommended

The GTK3-specific implementation is coherent, with only minor test resource-cleanup feedback remaining.

Review effort: Balanced
Findings: 2

Open (2)

• Dispose Image in finally when waitEvent assertion fails · New
• Dispose Image in finally when waitEvent assertion fails · New

Resolved since last review (4)

• Avoid unconditional GTK4 tree cell-data callbacks
• Avoid unconditional GTK4 table cell-data callbacks
• Set a nonzero tree size to exercise cell painting
• Set a nonzero table size to exercise cell painting

[Copilot]

Copilot review overview

🟡 Changes recommended

Stale non-owning surface addresses can alias replacement surfaces and render the wrong image.

Review effort: Balanced
Findings: 2

Open (2)

• Stale surface pointer aliases replacement image after slot reuse · New
• Stale surface pointer aliases replacement image after slot reuse · New

Resolved since last review (2)

• Dispose Image in finally when waitEvent assertion fails
• Dispose Image in finally when waitEvent assertion fails

[Copilot]

Copilot review overview

🟢 Approval recommended

The rendering and ownership changes are coherent and tested; only a minor class-reference cleanup remains.

Review effort: Balanced
Findings: 1

Open (1)

• Unref class returned by g_type_class_ref · New

Resolved since last review (2)

• Stale surface pointer aliases replacement image after slot reuse
• Stale surface pointer aliases replacement image after slot reuse

[vogella]

Fixed