Optimization fixed.

The biggest problem was more severe than expected: while dragging a Rectangle or Ellipse Selection, LinXPaint was rebuilding a document-sized selection mask on every mouse movement. Marching ants then scanned that full mask, and antialiased selection could create a 4× supersampled canvas-sized mask. On an 8K image, simply moving the mouse could therefore trigger enormous amounts of unnecessary work.

That has been redesigned.

Rectangle and Ellipse Selection now use geometry-only live previews while you drag. The actual selection mask is constructed once when the mouse is released. Replace, Add, Subtract, Intersect and XOR behavior is preserved.

On a 2800×1800 test:

• four selection-drag updates: ~1.86 seconds → ~0.00004 seconds
• the actual mask commit occurs once on release: ~0.03 seconds
• an 8K selection drag is likewise essentially immediate while moving

I also found several secondary problems contributing to the feeling that “live preview” was slow.

Adjustment/effect previews with an active selection previously:

• compressed the complete layer before previewing
• copied the complete selection mask
• processed the complete image even if only a small selected region mattered
• created complete-image Undo snapshots when Apply was pressed

That is now localized.

For an 800×600 selection inside a 2800×1800 document:

• first preview setup: ~0.646 s → ~0.00034 s
• actual adjustment preview: ~0.57–0.69 s → ~0.11–0.12 s
• selected adjustment Apply: ~0.78 s → ~0.13 s
• selected Apply history storage: ~34.9 MiB → ~3.2 MiB

The preview result remains pixel-identical.