PPTX: outer shadows render as crisp offset duplicates without blur

[developer0hye]

Summary

Outer shadows (shapes and, since #360, pictures) render as a crisp offset duplicate with reduced opacity. PowerPoint blurs the shadow (blurRad) and spreads it around the element, so its soft frame extends on all sides; office2pdf's approximation only shows the offset band on the far side. Typst has no blur primitive, so a faithful version needs layered rects/polygons with graduated alpha or a pre-rendered raster.

Reproduction

Convert a PPTX shape or picture with a:outerShdw blurRad="114300" dist="38100" dir="5400000" and compare the shadow's softness/extent with a PowerPoint PDF export at 150 DPI.

Expected

A soft shadow spreading blurRad around the element, strongest along the offset direction.

Actual

A hard-edged offset duplicate visible only on the offset side.

Related

Related: #360

Visual comparison

Ground truth is on the left; office2pdf output at filing time (after #360's offset approximation) is on the right, rendered with pdftoppm at 150 DPI.

[developer0hye]

Fixed by #400 (merged). Outer shadows now render as four concentric translucent layers spanning blurRad/2 inset to blurRad/2 outset, whose alphas compound to the shadow opacity at the core and fade at the rim — a soft graduated frame instead of a crisp offset duplicate. Verified against native PowerPoint GT at 150 DPI on the quarterly-review card (pixel sweep 0.43%). Evidence: assets/bugfixes/issue-390/.

[developer0hye]

Fresh 150-DPI audit on main at 775b492 still shows hard-edged offset duplicates instead of blurred outer shadows. It repeats across business slides including startup pitch slide 3, quarterly review slide 2, training deck slide 3, company intro slide 3, marketing report slide 2, and sales proposal slide 2. Element geometry, fills, and text remain present. Reopening because the issue closing condition is not met.