[tarai-dl]

Problem

DropShadowFilter has severe performance issues on Apple devices (Mac/iPhone) with Retina displays. On these devices, the filter runs at ~3 FPS even with low quality settings.

Root Cause

The inner KawaseBlurFilter was not receiving the resolution parameter from the parent DropShadowFilter. Without an explicit resolution, PixiJS's filter system defaults to inheriting the renderer's devicePixelRatio. On Apple Retina displays (DPR 2-3x), this causes the blur to be rendered at 2-3x the necessary resolution, resulting in 4-9x more pixels to process.

Changes

1. Pass resolution to KawaseBlurFilter: Set this._blurFilter.resolution to match the parent filter's resolution (lines 152-156)
2. Recalculate padding on runtime changes: Added _updatePadding() calls when kernels, pixelSize, pixelSizeX, or pixelSizeY are modified at runtime (similar to PR fix(drop-shadow): recalc padding when kernel/pixel size changes #520)

Impact

• On Apple Retina displays (DPR 2x): ~4x fewer pixels processed by blur → significant FPS improvement
• On Apple Retina displays (DPR 3x): ~9x fewer pixels processed by blur → dramatic FPS improvement
• No visual regression: the blur quality at resolution=1 is sufficient for drop shadow effects
• Backward compatible: no API changes

Related

• Fixes DropShadowFilter low performance on Macs and iPhones #327
• Addresses the root cause identified by @majinjacques in the issue comments
• Supersedes the padding-only fix in fix(drop-shadow): recalc padding when kernel/pixel size changes #520 (included in this PR)

Testing

The fix can be verified by checking that DropShadowFilter._blurFilter.resolution equals the filter's resolution on construction, rather than defaulting to the renderer's DPR.