LibPDF: Sketch out DeviceN color spaces a bit

Documents using them now show render-time diagnostics instead
of asserting that number of parameters passed to a color don't
match whatever number of channels the previously-set color space
had.

Fixes two asserts on the `-n 500` 0000.zip test set.

Userland/Libraries/LibPDF/ColorSpace.cpp

@@ -56,6 +56,9 @@ PDFErrorOr<NonnullRefPtr<ColorSpace>> ColorSpace::create(Document* document, Non
     if (color_space_name == CommonNames::CalRGB)
         return TRY(CalRGBColorSpace::create(document, move(parameters)));
 
+    if (color_space_name == CommonNames::DeviceN)
+        return TRY(DeviceNColorSpace::create(document, move(parameters)));
+
     if (color_space_name == CommonNames::ICCBased)
         return TRY(ICCBasedColorSpace::create(document, move(parameters)));
 
@@ -134,6 +137,51 @@ Vector<float> DeviceCMYKColorSpace::default_decode() const
     return { 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, 1.0f };
 }
 
+PDFErrorOr<NonnullRefPtr<DeviceNColorSpace>> DeviceNColorSpace::create(Document*, Vector<Value>&& parameters)
+{
+    // "[ /DeviceN names alternateSpace tintTransform ]
+    //  or
+    //  [ /DeviceN names alternateSpace tintTransform attributes ]"
+    if (parameters.size() != 4 && parameters.size() != 5)
+        return Error { Error::Type::MalformedPDF, "DevicN color space expects 4 or 5 parameters" };
+
+    // "The names parameter is an array of name objects specifying the individual color components.
+    //  The length of the array determines the number of components in the DeviceN color space"
+    auto names = parameters[0].get<NonnullRefPtr<Object>>()->cast<ArrayObject>();
+
+    // "The alternateSpace parameter is an array or name object that can be any device or CIE-based color space
+    //  but not another special color space (Pattern, Indexed, Separation, or DeviceN)."
+
+    // FIXME: Implement.
+
+    return adopt_ref(*new DeviceNColorSpace(names->size()));
+}
+
+PDFErrorOr<Color> DeviceNColorSpace::color(ReadonlySpan<Value>) const
+{
+    return Error::rendering_unsupported_error("DeviceN color spaces not yet implemented");
+}
+
+int DeviceNColorSpace::number_of_components() const
+{
+    return m_number_of_components;
+}
+
+Vector<float> DeviceNColorSpace::default_decode() const
+{
+    Vector<float> decoding_ranges;
+    for (u8 i = 0; i < number_of_components(); i++) {
+        decoding_ranges.append(0.0);
+        decoding_ranges.append(1.0);
+    }
+    return decoding_ranges;
+}
+
+DeviceNColorSpace::DeviceNColorSpace(size_t number_of_components)
+    : m_number_of_components(number_of_components)
+{
+}
+
 PDFErrorOr<NonnullRefPtr<CalRGBColorSpace>> CalRGBColorSpace::create(Document* document, Vector<Value>&& parameters)
 {
     if (parameters.size() != 1)

Userland/Libraries/LibPDF/ColorSpace.h

@@ -106,6 +106,23 @@ private:
     DeviceCMYKColorSpace() = default;
 };
 
+class DeviceNColorSpace final : public ColorSpace {
+public:
+    static PDFErrorOr<NonnullRefPtr<DeviceNColorSpace>> create(Document*, Vector<Value>&& parameters);
+
+    ~DeviceNColorSpace() override = default;
+
+    PDFErrorOr<Color> color(ReadonlySpan<Value> arguments) const override;
+    int number_of_components() const override;
+    Vector<float> default_decode() const override;
+    ColorSpaceFamily const& family() const override { return ColorSpaceFamily::DeviceN; }
+
+private:
+    DeviceNColorSpace(size_t number_of_components);
+
+    size_t m_number_of_components { 0 };
+};
+
 class CalRGBColorSpace final : public ColorSpace {
 public:
     static PDFErrorOr<NonnullRefPtr<CalRGBColorSpace>> create(Document*, Vector<Value>&& parameters);

Userland/Libraries/LibPDF/CommonNames.h

@@ -51,6 +51,7 @@
     X(Dests)                      \
     X(DeviceCMYK)                 \
     X(DeviceGray)                 \
+    X(DeviceN)                    \
     X(DeviceRGB)                  \
     X(Differences)                \
     X(E)                          \