Add macOS backdrop blur and preserve PDF ink opacity

1 files changed, 15 insertions, 1 deletions

diff --git a/src/macos/Sources/PardesView.swift b/src/macos/Sources/PardesView.swift
index 7c537055..7981cf46 100644
--- a/src/macos/Sources/PardesView.swift
+++ b/src/macos/Sources/PardesView.swift
@@ -1446,6 +1446,7 @@ final class PardesView: NSView {
         let source: CGRect
         let body: CGRect
         let destination: CGRect
+        let paperBG: UInt32
     }
 
     /// Rasterized attachments, decoded once each. The bytes the core lends are
@@ -1496,7 +1497,7 @@ final class PardesView: NSView {
                 height: CGFloat(place.dst_h) / scale)
             let frozen = FrozenImage(
                 key: key, image: crop, source: source,
-                body: body, destination: dst)
+                body: body, destination: dst, paperBG: place.paper_bg)
             frameImages.append(frozen)
             drawFrozenImage(ctx, frozen)
         }
@@ -1545,11 +1546,24 @@ final class PardesView: NSView {
         ctx.clip(to: placed.body)
         // isFlipped gives us a y-down CTM and CGImage draws +y up, so flip
         // about this destination rather than changing the grid arithmetic.
+        let isPDF = placed.paperBG != UInt32(PARDES_COLOR_DEFAULT)
+        if isPDF {
+            fillBackground(ctx, placed.destination, placed.paperBG, backgroundAlpha)
+        }
         ctx.translateBy(x: placed.destination.minX, y: placed.destination.maxY)
         ctx.scaleBy(x: 1, y: -1)
         ctx.interpolationQuality = .high
         let rect = CGRect(x: 0, y: 0,
                           width: placed.destination.width, height: placed.destination.height)
+        if isPDF {
+            // Paper was painted at WindowOpacity. Content keeps the PDF's own
+            // coverage, so glyphs, photos and paths stay legible at zero opacity.
+            ctx.setAlpha(1)
+            ctx.setBlendMode(.normal)
+            ctx.draw(placed.image, in: rect)
+            ctx.restoreGState()
+            return
+        }
         // Match image.frag.glsl/backgroundLayerBlend: source coverage removes
         // the destination independently of WindowOpacity, then the source is
         // added at that opacity. Ordinary source-over would compound alpha;