Add macOS backdrop blur and preserve PDF ink opacity

2 files changed, 28 insertions, 12 deletions

diff --git a/src/macos/Sources/AppDelegate.swift b/src/macos/Sources/AppDelegate.swift
index 4e91e407..cbe9cdc9 100644
--- a/src/macos/Sources/AppDelegate.swift
+++ b/src/macos/Sources/AppDelegate.swift
@@ -81,8 +81,8 @@ final class AppDelegate: NSObject, NSApplicationDelegate, PardesViewDelegate {
         // The grid and the blur are SIBLINGS in a plain container, not parent
         // and child. A transparent theme has to show something through the
         // grid, and AppKit will not blur what is behind a window unless an
-        // NSVisualEffectView asks it to — but the backdrop is hidden for every
-        // theme that brings its own background, and hiding a superview hides
+        // NSVisualEffectView asks it to. The backdrop can be hidden independently
+        // when blur is disabled or the ground is opaque; hiding a superview hides
         // its subviews with it. Nested, an opaque theme drew a blank window.
         let container = NSView(frame: NSRect(origin: .zero, size: want))
         container.autoresizesSubviews = true
@@ -460,6 +460,7 @@ final class AppDelegate: NSObject, NSApplicationDelegate, PardesViewDelegate {
     /// theme whose background happened to equal the view's starting guess
     /// would otherwise leave the window in AppKit's default clothes forever.
     private var dressed = false
+    private var appliedBlur: UInt8 = 0
 
     private func applyTheme() {
         // Both reads happen every pump, and neither may be short-circuited by
@@ -468,15 +469,17 @@ final class AppDelegate: NSObject, NSApplicationDelegate, PardesViewDelegate {
         // tick would leave one of them unworn.
         let themeChanged = view.adoptThemeBG(pardes_theme_bg())
         let opacityChanged = view.adoptWindowOpacity(pardes_window_opacity())
-        guard themeChanged || opacityChanged || !dressed else { return }
+        let blur = pardes_window_blur()
+        let blurChanged = blur != appliedBlur
+        guard themeChanged || opacityChanged || blurChanged || !dressed else { return }
+        appliedBlur = blur
+        backdrop.alphaValue = CGFloat(blur) / 100
+        backdrop.isHidden = blur == 0 || (view.themeBG != nil && view.backgroundAlpha >= 1)
         dressed = true
-        // A ground short of solid needs the same non-opaque window a
-        // background-less theme does — but not the blur behind it. The backdrop
-        // answers "this theme brings no background"; WindowOpacity says how
-        // much of the one it brings to paint, and what shows through the rest
-        // is the desktop, which is what asking for a translucent window means.
+        // Opacity paints the theme ground; blur controls the native material
+        // behind it. An opaque ground hides the backdrop without losing the
+        // requested strength, so lowering opacity restores the effect.
         if let rgb = view.themeBG {
-            backdrop.isHidden = true
             window.isOpaque = view.backgroundAlpha >= 1
             window.backgroundColor = view.backgroundAlpha < 1 ? .clear : NSColor(
                 srgbRed: CGFloat((rgb >> 16) & 0xFF) / 255,
@@ -493,10 +496,9 @@ final class AppDelegate: NSObject, NSApplicationDelegate, PardesViewDelegate {
             window.appearance = NSAppearance(named: luma > 0.5 ? .aqua : .darkAqua)
         } else {
             // Transparent: the window stops painting anything of its own and
-            // the blur takes over. isOpaque false is what lets the desktop
+            // the optional blur sits behind it. isOpaque false lets the desktop
             // reach the backdrop at all — a titled window is opaque by default
             // and would composite over it.
-            backdrop.isHidden = false
             window.isOpaque = false
             window.backgroundColor = .clear
             window.appearance = NSAppearance(named: .darkAqua)
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;