fix(print): anchor raster at page top in bottom-up canvas space (#211)

226e7b2 un-flipped the canvas but left destinationRect anchored at
pageRect.minY — the page's BOTTOM edge in bottom-up space — so
sub-page targets printed at the foot of the sheet and oversize
targets clipped their top rows. Anchor at pageRect.maxY - height,
restoring the spec'd top-left anchor (docs/14 §6, D9).

Adds the missing regression coverage: the geometry test now asserts
the top anchor with a sub-page raster, and the PDF harness gains a
banded (red-over-blue) fixture that fails on either a mirrored draw
or a bottom anchor — solid fills could catch neither.

Sources/ICCery/Print/TargetPageCanvasView.swift

@@ -27,8 +27,10 @@ final class TargetPageCanvasView: NSView {
         fatalError("TargetPageCanvasView is code-only")
     }
 
-    /// Flipped: the CoreGraphics coordinate space is correctly oriented
-    /// top-down, so page 1 is the TOP rect.
+    /// Bottom-up CoreGraphics space: `CGContext.draw(_:in:)` renders
+    /// the raster upright — a flipped view prints mirrored (#211).
+    /// Page 1 is the BOTTOM band of the frame, the non-flipped
+    /// pagination convention.
     override var isFlipped: Bool { false }
     override var isOpaque: Bool { true }
 
@@ -37,7 +39,7 @@ final class TargetPageCanvasView: NSView {
         return true
     }
 
-    /// 1-based page → its paper-sized rect, stacked top-down.
+    /// 1-based page → its paper-sized rect, stacked bottom-up.
     override func rectForPage(_ page: Int) -> NSRect {
         NSRect(x: 0,
                y: CGFloat(page - 1) * paperSize.height,
@@ -53,7 +55,7 @@ final class TargetPageCanvasView: NSView {
         let pageRect = rectForPage(page)
         let size = pages[page - 1].pointSize
         return NSRect(x: Self.snap(pageRect.minX),
-                      y: Self.snap(pageRect.minY),
+                      y: Self.snap(pageRect.maxY - size.height),
                       width: size.width,
                       height: size.height)
     }

Tests/ICCeryCoreTests/NativeSpoolPDFTests.swift

@@ -40,21 +40,8 @@ final class NativeSpoolPDFTests: XCTestCase {
             pixelBytes: patchBytes, in: tempRoot)
         let raster = try TargetRasterLoader.load(tiff: tiff)
 
-        let info = NSPrintInfo()
-        info.paperSize = paperSize
-        info.orientation = .portrait
-        info.topMargin = 0
-        info.bottomMargin = 0
-        info.leftMargin = 0
-        info.rightMargin = 0
-        info.horizontalPagination = .clip
-        info.verticalPagination = .clip
-        info.scalingFactor = 1.0
-        info.isHorizontallyCentered = false
-        info.isVerticallyCentered = false
-        info.jobDisposition = .save
         let pdfURL = tempRoot.appendingPathComponent("spool.pdf")
-        info.dictionary()[NSPrintInfo.AttributeKey.jobSavingURL] = pdfURL
+        let info = makeSaveInfo(pdfURL: pdfURL)
 
         let canvas = TargetPageCanvasView(
             pages: [raster, raster], paperSize: paperSize)
@@ -88,29 +75,7 @@ final class NativeSpoolPDFTests: XCTestCase {
     ) throws {
         let width = Int(ceil(mediaBox.width))
         let height = Int(ceil(mediaBox.height))
-        let rep = try XCTUnwrap(NSBitmapImageRep(
-            bitmapDataPlanes: nil,
-            pixelsWide: width,
-            pixelsHigh: height,
-            bitsPerSample: 8,
-            samplesPerPixel: 4,
-            hasAlpha: true,
-            isPlanar: false,
-            colorSpaceName: .deviceRGB,
-            bytesPerRow: 0,
-            bitsPerPixel: 0))
-        let context = try XCTUnwrap(
-            NSGraphicsContext(bitmapImageRep: rep))
-        let cg = context.cgContext
-        let transform = page.getDrawingTransform(
-            .mediaBox,
-            rect: CGRect(x: 0, y: 0, width: width, height: height),
-            rotate: 0, preserveAspectRatio: true)
-        NSGraphicsContext.saveGraphicsState()
-        NSGraphicsContext.current = context
-        cg.concatenate(transform)
-        cg.drawPDFPage(page)
-        NSGraphicsContext.restoreGraphicsState()
+        let rep = try renderPageToBitmap(page, mediaBox: mediaBox)
 
         func pixel(_ x: Int, _ y: Int) throws -> (Double, Double, Double) {
             let color = try XCTUnwrap(
@@ -161,4 +126,144 @@ final class NativeSpoolPDFTests: XCTestCase {
         XCTAssertEqual(outside.1, 1, accuracy: 0.04)
         XCTAssertEqual(outside.2, 1, accuracy: 0.04)
     }
+
+    /// #211 — a top/bottom banded block proves the page is drawn
+    /// upright AND anchored at the paper's top edge: a mirrored draw
+    /// swaps the bands; a bottom-anchored draw leaves white above the
+    /// block instead of below.
+    func testSavePDFDrawsPageUprightTopAnchored() throws {
+        try XCTSkipIf(
+            ProcessInfo.processInfo.environment["ICCERY_SKIP_PRINT_PDF"]
+                == "1",
+            "ICCERY_SKIP_PRINT_PDF=1 — print system unavailable")
+
+        // 144×144 px @ 72 dpi → a 144×144 pt block, top half red,
+        // bottom half blue.
+        let topBytes: [UInt8] = [230, 40, 50]
+        let bottomBytes: [UInt8] = [40, 50, 230]
+        let tiff = try TargetTestFixtures.makeTIFF(
+            px: CGSize(width: 144, height: 144), dpi: 72,
+            components: 3, bitsPerComponent: 8,
+            pixelBytes: topBytes,
+            bottomHalfPixelBytes: bottomBytes, in: tempRoot)
+        let raster = try TargetRasterLoader.load(tiff: tiff)
+
+        let pdfURL = tempRoot.appendingPathComponent("bands.pdf")
+        let info = makeSaveInfo(pdfURL: pdfURL)
+        let canvas = TargetPageCanvasView(
+            pages: [raster], paperSize: paperSize)
+        let operation = NSPrintOperation(view: canvas, printInfo: info)
+        operation.showsPrintPanel = false
+        operation.showsProgressPanel = false
+        operation.canSpawnSeparateThread = false
+        XCTAssertTrue(operation.run(),
+                      "NSPrintOperation.save failed")
+
+        let document = try XCTUnwrap(
+            CGPDFDocument(pdfURL as CFURL))
+        let page = try XCTUnwrap(document.page(at: 1))
+        let mediaBox = page.getBoxRect(.mediaBox)
+        let rep = try renderPageToBitmap(page, mediaBox: mediaBox)
+
+        func pixel(_ x: Int, _ y: Int) throws -> (Double, Double, Double) {
+            let color = try XCTUnwrap(
+                rep.colorAt(x: x, y: y)?.usingColorSpace(.deviceRGB))
+            return (color.redComponent,
+                    color.greenComponent,
+                    color.blueComponent)
+        }
+        func matches(
+            _ p: (Double, Double, Double), _ rgb: [UInt8]
+        ) -> Bool {
+            abs(p.0 - Double(rgb[0]) / 255) < 0.04
+                && abs(p.1 - Double(rgb[1]) / 255) < 0.04
+                && abs(p.2 - Double(rgb[2]) / 255) < 0.04
+        }
+
+        // Painted region = the page fill inset by the queue's
+        // unprintable margin (R10); minimum opaque y is its top edge
+        // in the rendered bitmap (same convention as the 1:1 test).
+        let width = Int(ceil(mediaBox.width))
+        let height = Int(ceil(mediaBox.height))
+        var topX = width, topY = height
+        for y in 0..<height {
+            for x in 0..<width
+            where (rep.colorAt(x: x, y: y)?.alphaComponent ?? 0) > 0.5 {
+                topX = min(topX, x)
+                topY = min(topY, y)
+            }
+        }
+        XCTAssertLessThan(topY, height, "PDF page rendered empty")
+
+        // The 144 pt block hangs from the page's top edge: top-band
+        // colour for the first 72 pt, bottom-band colour for the
+        // next 72 pt, then the white page fill.
+        XCTAssertTrue(
+            try matches(pixel(topX + 10, topY + 10), topBytes),
+            "block top is not the top-band colour — mirrored draw?")
+        XCTAssertTrue(
+            try matches(pixel(topX + 10, topY + 82), bottomBytes),
+            "block bottom is not the bottom-band colour — mirrored draw?")
+        XCTAssertTrue(
+            try matches(pixel(topX + 10, topY + 134), bottomBytes),
+            "block does not reach 144 pt below the painted top edge")
+        let below = try pixel(topX + 10, topY + 160)
+        XCTAssertEqual(below.0, 1, accuracy: 0.04)
+        XCTAssertEqual(below.1, 1, accuracy: 0.04)
+        XCTAssertEqual(below.2, 1, accuracy: 0.04)
+    }
+
+    /// Print settings shared by the save-PDF harness tests: A4, zero
+    /// margins, `.clip` pagination, 1:1, no centring, `.save` to
+    /// `pdfURL`.
+    private func makeSaveInfo(pdfURL: URL) -> NSPrintInfo {
+        let info = NSPrintInfo()
+        info.paperSize = paperSize
+        info.orientation = .portrait
+        info.topMargin = 0
+        info.bottomMargin = 0
+        info.leftMargin = 0
+        info.rightMargin = 0
+        info.horizontalPagination = .clip
+        info.verticalPagination = .clip
+        info.scalingFactor = 1.0
+        info.isHorizontallyCentered = false
+        info.isVerticallyCentered = false
+        info.jobDisposition = .save
+        info.dictionary()[
+            NSPrintInfo.AttributeKey.jobSavingURL] = pdfURL
+        return info
+    }
+
+    /// Render a saved-PDF page into a bitmap at 1 px/pt.
+    private func renderPageToBitmap(
+        _ page: CGPDFPage, mediaBox: CGRect
+    ) throws -> NSBitmapImageRep {
+        let width = Int(ceil(mediaBox.width))
+        let height = Int(ceil(mediaBox.height))
+        let rep = try XCTUnwrap(NSBitmapImageRep(
+            bitmapDataPlanes: nil,
+            pixelsWide: width,
+            pixelsHigh: height,
+            bitsPerSample: 8,
+            samplesPerPixel: 4,
+            hasAlpha: true,
+            isPlanar: false,
+            colorSpaceName: .deviceRGB,
+            bytesPerRow: 0,
+            bitsPerPixel: 0))
+        let context = try XCTUnwrap(
+            NSGraphicsContext(bitmapImageRep: rep))
+        let cg = context.cgContext
+        let transform = page.getDrawingTransform(
+            .mediaBox,
+            rect: CGRect(x: 0, y: 0, width: width, height: height),
+            rotate: 0, preserveAspectRatio: true)
+        NSGraphicsContext.saveGraphicsState()
+        NSGraphicsContext.current = context
+        cg.concatenate(transform)
+        cg.drawPDFPage(page)
+        NSGraphicsContext.restoreGraphicsState()
+        return rep
+    }
 }

Tests/ICCeryCoreTests/TargetCanvasGeometryTests.swift

@@ -4,7 +4,7 @@ import Foundation
 import XCTest
 @testable import ICCery
 
-/// Issue #201 Phase 3 — `TargetPageCanvasView` top-down page stacking,
+/// Issue #201 Phase 3 — `TargetPageCanvasView` bottom-up page stacking,
 /// snapped top-left anchoring, and the draw-time interpolation /
 /// antialias contract asserted via `drawProbe`.
 @MainActor
@@ -35,7 +35,9 @@ final class TargetCanvasGeometryTests: XCTestCase {
 
     // MARK: - Page stacking
 
-    func testRectForPageStacksTopDown() {
+    /// Bottom-up space: page 1 is the BOTTOM band of the frame — the
+    /// non-flipped pagination convention (#211).
+    func testRectForPageStacksBottomUp() {
         let view = TargetPageCanvasView(
             pages: [raster(), raster(), raster()],
             paperSize: paperSize)
@@ -68,18 +70,33 @@ final class TargetCanvasGeometryTests: XCTestCase {
             pages: [raster(), raster()],
             paperSize: paperSize)
 
+        // Near-full-page raster: in bottom-up space the page's top
+        // edge is `maxY`, so the top-anchored origin is ~0.03 pt
+        // negative — the overflow clips at the BOTTOM of the sheet.
         let first = view.destinationRect(forPage: 1)
         XCTAssertEqual(first.origin.x, 0, accuracy: 0.001)
-        XCTAssertEqual(first.origin.y, 0, accuracy: 0.001)
+        XCTAssertEqual(first.origin.y, -0.03, accuracy: 0.001)
         XCTAssertEqual(first.width, 595.2, accuracy: 0.01)
         XCTAssertEqual(first.height, 841.92, accuracy: 0.01)
 
         let second = view.destinationRect(forPage: 2)
         XCTAssertEqual(
-            second.origin.y, paperSize.height, accuracy: 0.001)
+            second.origin.y,
+            2 * paperSize.height - first.height, accuracy: 0.001)
         XCTAssertEqual(second.size, first.size)
 
-        for rect in [first, second] {
+        // A raster smaller than the paper hangs from the page's TOP
+        // edge — minY would anchor it at the bottom (#211 follow-up).
+        let small = TargetPageCanvasView(
+            pages: [raster(pixelWidth: 72, pixelHeight: 72, dpi: 72)],
+            paperSize: paperSize)
+        let smallRect = small.destinationRect(forPage: 1)
+        XCTAssertEqual(smallRect.origin.x, 0, accuracy: 0.001)
+        XCTAssertEqual(
+            smallRect.origin.y, paperSize.height - 72, accuracy: 0.001)
+        XCTAssertEqual(smallRect.size, CGSize(width: 72, height: 72))
+
+        for rect in [first, second, smallRect] {
             XCTAssertEqual(
                 rect.origin.x * 1000,
                 (rect.origin.x * 1000).rounded(),

Tests/ICCeryCoreTests/TargetRasterFixtures.swift

@@ -27,12 +27,16 @@ enum TargetTestFixtures {
     /// colour space for 1/3/4 components at 8 or 16 bpc. `alpha: true`
     /// appends one alpha sample per pixel (`last`). `pixelBytes` is the
     /// repeating per-pixel pattern (big-endian for 16 bpc).
+    /// `bottomHalfPixelBytes`, when set, is the pattern for the bottom
+    /// half of the rows — a vertical asymmetry that lets tests catch a
+    /// mirrored draw (#211).
     static func makeImage(
         px: CGSize,
         components: Int,
         bitsPerComponent: Int,
         alpha: Bool = false,
-        pixelBytes: [UInt8]? = nil
+        pixelBytes: [UInt8]? = nil,
+        bottomHalfPixelBytes: [UInt8]? = nil
     ) -> CGImage? {
         let width = Int(px.width)
         let height = Int(px.height)
@@ -40,19 +44,31 @@ enum TargetTestFixtures {
         let samples = components + (alpha ? 1 : 0)
         let bytesPerPixel = samples * bytesPerComponent
         let bytesPerRow = width * bytesPerPixel
-        let pattern = pixelBytes
-            ?? Array(0..<bytesPerPixel).map { UInt8(($0 * 37 + 11) & 0xff) }
+        func buildRow(_ pattern: [UInt8]) -> [UInt8] {
             var row = [UInt8](repeating: 0, count: bytesPerRow)
-        for offset in stride(from: 0, to: bytesPerRow, by: pattern.count) {
+            for offset in stride(
+                from: 0, to: bytesPerRow, by: pattern.count) {
                 for (index, byte) in pattern.enumerated()
                 where offset + index < bytesPerRow {
                     row[offset + index] = byte
                 }
             }
+            return row
+        }
+        let topRow = buildRow(
+            pixelBytes
+                ?? Array(0..<bytesPerPixel).map {
+                    UInt8(($0 * 37 + 11) & 0xff)
+                })
+        let bottomRow = buildRow(bottomHalfPixelBytes ?? pixelBytes
+            ?? Array(0..<bytesPerPixel).map {
+                UInt8(($0 * 37 + 11) & 0xff)
+            })
         var bytes = [UInt8]()
         bytes.reserveCapacity(bytesPerRow * height)
-        for _ in 0..<height {
-            bytes.append(contentsOf: row)
+        for rowIndex in 0..<height {
+            bytes.append(
+                contentsOf: rowIndex < height / 2 ? topRow : bottomRow)
         }
         let data = Data(bytes)
 
@@ -88,6 +104,7 @@ enum TargetTestFixtures {
 
     /// Writes `makeImage` output to a single-page TIFF. `dpi` nil
     /// produces a TIFF with no resolution tags (the 72-fallback path).
+    /// `bottomHalfPixelBytes` passes through to `makeImage` (#211).
     static func makeTIFF(
         px: CGSize,
         dpi: Double?,
@@ -95,12 +112,14 @@ enum TargetTestFixtures {
         bitsPerComponent: Int = 8,
         alpha: Bool = false,
         pixelBytes: [UInt8]? = nil,
+        bottomHalfPixelBytes: [UInt8]? = nil,
         in directory: URL
     ) throws -> URL {
         guard let image = makeImage(
             px: px, components: components,
             bitsPerComponent: bitsPerComponent,
-            alpha: alpha, pixelBytes: pixelBytes)
+            alpha: alpha, pixelBytes: pixelBytes,
+            bottomHalfPixelBytes: bottomHalfPixelBytes)
         else { throw FixtureError.imageNotCreated }
         let url = directory.appendingPathComponent(
             "fixture-\(UUID().uuidString).tiff")