Windows 200% scaling Tree drag and drop outline figure has pink background

[Phillipus]

Windows 11
Display set to 200%
Eclipse 4.39.0 I20260123-1800

At 200% display scaling the background for the ghost figure when dragging and dropping tree items is pink. At 100% scaling it is transparent as expected.

Screen.Recording.2026-01-24.114054.mp4

[HeikoKlare]

I can already reproduce this in a 2025-12 IDE. Might be that the issue has ever been there when using monitor-specific scaling.

[Phillipus]

I can already reproduce this in a 2025-12 IDE. Might be that the issue has ever been there when using monitor-specific scaling.

Yes. If "Use monitor-specific UI scaling" is disabled in 2025-12 preferences it's OK.

[ShahzaibIbrahim]

Few observation:

The issue arises when:

• Zoom > 100%
• Monitor specific scaling is turned on
• Smooth scaling is enabled

Summary:
While handling Display.DI_GETDRAGIMAGE in Tree, SWT manually constructs the drag image by:
Computing a region covering all selected items (its correct, i checked)
Creating a 32-bpp top-down DIB (CreateDIBSection)
Rendering the tree content into the DIB via PrintWindow
Returning the bitmap to the shell via SHDRAGIMAGE

This logic works correctly when monitor-specific scaling is OFF, but produces visible background artifacts when monitor-specific scaling is ON and SWT uses smooth autoscaling.

Root Cause Analysis

1. Transparency mechanism used

The drag image relies on color-key transparency (SHDRAGIMAGE.crColorKey). The background of the DIB is filled with a solid color before rendering.

2. PrintWindow limitations

PrintWindow only renders RGB data. It does not initialize or define alpha values, even in a 32-bpp DIB. As a result, the alpha channel is undefined or effectively ignored.

My deduction

In smooth scaling we SHDRAGIMAGE convert the image to RGBA?? and we no longer have matching crColorKey so the transparent pixel becomes visible to us.

[akoch-yatta]

PR #3027 was merged

[Phillipus]

Thanks to all!