Use transparent backgrounds for file preview panels

GhosttyTabs.xcodeproj/project.pbxproj

@@ -83,6 +83,7 @@
 		D0B1001CA1B2C3D4E5F60001 /* PaneDropRoutingSupport.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0B1001DA1B2C3D4E5F60001 /* PaneDropRoutingSupport.swift */; };
 		D0B1001EA1B2C3D4E5F60001 /* BrowserPaneDropTargetView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0B1001FA1B2C3D4E5F60001 /* BrowserPaneDropTargetView.swift */; };
 		D0B10016A1B2C3D4E5F60001 /* FilePreviewTextEditor.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0B10017A1B2C3D4E5F60001 /* FilePreviewTextEditor.swift */; };
+		A5001450A5001450A5001450 /* FilePreviewNativeBackground.swift in Sources */ = {isa = PBXBuildFile; fileRef = A5001451A5001451A5001451 /* FilePreviewNativeBackground.swift */; };
 		D0B10018A1B2C3D4E5F60001 /* FileDropOverlayViewTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0B10019A1B2C3D4E5F60001 /* FileDropOverlayViewTests.swift */; };
 		D7AB34300000000000000001 /* SidebarDropPlanner.swift in Sources */ = {isa = PBXBuildFile; fileRef = D7AB34300000000000000002 /* SidebarDropPlanner.swift */; };
 		D7AB34300000000000000003 /* SidebarBonsplitTabWorkspaceDropOverlay.swift in Sources */ = {isa = PBXBuildFile; fileRef = D7AB34300000000000000004 /* SidebarBonsplitTabWorkspaceDropOverlay.swift */; };
@@ -684,6 +685,7 @@
 		D0B1001DA1B2C3D4E5F60001 /* PaneDropRoutingSupport.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PaneDropRoutingSupport.swift; sourceTree = "<group>"; };
 		D0B1001FA1B2C3D4E5F60001 /* BrowserPaneDropTargetView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BrowserPaneDropTargetView.swift; sourceTree = "<group>"; };
 		D0B10017A1B2C3D4E5F60001 /* FilePreviewTextEditor.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Panels/FilePreviewTextEditor.swift; sourceTree = "<group>"; };
+		A5001451A5001451A5001451 /* FilePreviewNativeBackground.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Panels/FilePreviewNativeBackground.swift; sourceTree = "<group>"; };
 		A5001016 /* GhosttyKit.xcframework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.xcframework; path = GhosttyKit.xcframework; sourceTree = "<group>"; };
 		A5001017 /* ghostty.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = ghostty.h; sourceTree = "<group>"; };
 		A5001018 /* cmux-Bridging-Header.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "cmux-Bridging-Header.h"; sourceTree = "<group>"; };
@@ -1306,6 +1308,7 @@
 				A50014F1 /* MarkdownViewerAssets.swift */,
 				A5001423 /* FilePreviewPanel.swift */,
 				D0B10017A1B2C3D4E5F60001 /* FilePreviewTextEditor.swift */,
+				A5001451A5001451A5001451 /* FilePreviewNativeBackground.swift */,
 				A5001442A5001442A5001442 /* FilePreviewModeSupport.swift */,
 				A5001444A5001444A5001444 /* FilePreviewWorkspaceOpenSupport.swift */,
 				A5001446A5001446A5001446 /* FilePreviewMagnifyingPDFView.swift */,
@@ -1985,6 +1988,7 @@
 				A50014F3 /* MarkdownViewerAssets.swift in Sources */,
 				A5001422 /* FilePreviewPanel.swift in Sources */,
 				D0B10016A1B2C3D4E5F60001 /* FilePreviewTextEditor.swift in Sources */,
+				A5001450A5001450A5001450 /* FilePreviewNativeBackground.swift in Sources */,
 				A5001443A5001443A5001443 /* FilePreviewModeSupport.swift in Sources */,
 				A5001445A5001445A5001445 /* FilePreviewWorkspaceOpenSupport.swift in Sources */,
 				A5001447A5001447A5001447 /* FilePreviewMagnifyingPDFView.swift in Sources */,

Sources/Panels/FilePreviewNativeBackground.swift

@@ -0,0 +1,65 @@
+import AppKit
+
+enum FilePreviewNativeBackground {
+    static func resolvedColor(backgroundColor: NSColor, drawsBackground: Bool) -> NSColor {
+        drawsBackground ? backgroundColor : .clear
+    }
+
+    static func applyRootLayer(
+        to view: NSView,
+        backgroundColor: NSColor,
+        drawsBackground: Bool
+    ) {
+        let resolvedBackgroundColor = resolvedColor(
+            backgroundColor: backgroundColor,
+            drawsBackground: drawsBackground
+        )
+        view.wantsLayer = true
+        view.layer?.backgroundColor = resolvedBackgroundColor.cgColor
+        view.layer?.isOpaque = drawsBackground && resolvedBackgroundColor.alphaComponent >= 0.999
+    }
+
+    static func applyScrollBackgrounds(
+        in view: NSView,
+        backgroundColor: NSColor,
+        drawsBackground: Bool
+    ) {
+        let resolvedBackgroundColor = resolvedColor(
+            backgroundColor: backgroundColor,
+            drawsBackground: drawsBackground
+        )
+        if let scrollView = view as? NSScrollView {
+            scrollView.drawsBackground = drawsBackground
+            scrollView.backgroundColor = resolvedBackgroundColor
+        }
+        if let clipView = view as? NSClipView {
+            clipView.drawsBackground = drawsBackground
+            clipView.backgroundColor = resolvedBackgroundColor
+        }
+        for subview in view.subviews {
+            applyScrollBackgrounds(
+                in: subview,
+                backgroundColor: backgroundColor,
+                drawsBackground: drawsBackground
+            )
+        }
+    }
+
+    static func scrollBackgroundHostIdentifiers(in view: NSView) -> Set<ObjectIdentifier> {
+        var identifiers = Set<ObjectIdentifier>()
+        collectScrollBackgroundHostIdentifiers(in: view, into: &identifiers)
+        return identifiers
+    }
+
+    private static func collectScrollBackgroundHostIdentifiers(
+        in view: NSView,
+        into identifiers: inout Set<ObjectIdentifier>
+    ) {
+        if view is NSScrollView || view is NSClipView {
+            identifiers.insert(ObjectIdentifier(view))
+        }
+        for subview in view.subviews {
+            collectScrollBackgroundHostIdentifiers(in: subview, into: &identifiers)
+        }
+    }
+}