Trade: add a MaterialData::attributeData(layer, id) accessor.

For cases where the whole MaterialAttributeData instance is needed and
calculating the right offset into the array returned by attributeData()
would be too error-prone.

Similar accessor is in MeshData already, so this achieves better feature
parity between the two.

src/Magnum/Trade/MaterialData.cpp

@@ -748,6 +748,14 @@ UnsignedInt MaterialData::attributeId(const MaterialLayer layer, const MaterialA
     return attributeId(string, name);
 }
 
+const MaterialAttributeData& MaterialData::attributeData(const UnsignedInt layer, const UnsignedInt id) const {
+    CORRADE_ASSERT(layer < layerCount(),
+        "Trade::MaterialData::attributeData(): index" << layer << "out of range for" << layerCount() << "layers", _data[0]);
+    CORRADE_ASSERT(id < attributeCount(layer),
+        "Trade::MaterialData::attributeData(): index" << id << "out of range for" << attributeCount(layer) << "attributes in layer" << layer, _data[0]);
+    return _data[layerOffset(layer) + id];
+}
+
 Containers::StringView MaterialData::attributeName(const UnsignedInt layer, const UnsignedInt id) const {
     CORRADE_ASSERT(layer < layerCount(),
         "Trade::MaterialData::attributeName(): index" << layer << "out of range for" << layerCount() << "layers", {});

src/Magnum/Trade/MaterialData.h

@@ -2451,6 +2451,23 @@ class MAGNUM_TRADE_EXPORT MaterialData {
             return attributeId(0, name);
         } /**< @overload */
 
+        /**
+         * @brief Raw attribute data
+         *
+         * The @p layer is expected to be smaller than @ref layerCount() const,
+         * @p id is expected to be smaller than @ref attributeCount(UnsignedInt) const.
+         */
+        const MaterialAttributeData& attributeData(UnsignedInt layer, UnsignedInt id) const;
+
+        /**
+         * @brief Raw attribute data in the base material
+         *
+         * The @p @p id is expected to be smaller than @ref attributeCount() const.
+         */
+        const MaterialAttributeData& attributeData(UnsignedInt id) const {
+            return attributeData(0, id);
+        }
+
         /**
          * @brief Name of an attribute in given material layer
          *

src/Magnum/Trade/Test/MaterialDataTest.cpp

@@ -998,6 +998,11 @@ void MaterialDataTest::construct() {
     CORRADE_COMPARE(data.attributeName(3), "highlightColor");
 
     /* Access by ID */
+    CORRADE_COMPARE(data.attributeData(0).name(), "AmbientTextureMatrix");
+    CORRADE_COMPARE(data.attributeData(1).name(), "DiffuseTextureCoordinates");
+    CORRADE_COMPARE(data.attributeData(2).name(), "DoubleSided");
+    CORRADE_COMPARE(data.attributeData(3).name(), "highlightColor");
+
     CORRADE_COMPARE(data.attributeType(0), MaterialAttributeType::Matrix3x3);
     CORRADE_COMPARE(data.attributeType(1), MaterialAttributeType::UnsignedInt);
     CORRADE_COMPARE(data.attributeType(2), MaterialAttributeType::Bool);
@@ -1220,6 +1225,10 @@ void MaterialDataTest::constructLayers() {
     CORRADE_COMPARE(data.attributeName(3, 1), "thickness");
 
     /* Access by layer ID and attribute ID */
+    CORRADE_COMPARE(data.attributeData(0, 0).name(), "DiffuseTextureCoordinates");
+    CORRADE_COMPARE(data.attributeData(1, 2).name(), "highlightColor");
+    CORRADE_COMPARE(data.attributeData(3, 1).name(), "thickness");
+
     CORRADE_COMPARE(data.attributeType(0, 0), MaterialAttributeType::UnsignedInt);
     CORRADE_COMPARE(data.attributeType(1, 2), MaterialAttributeType::Vector4);
     CORRADE_COMPARE(data.attributeType(3, 1), MaterialAttributeType::Float);
@@ -2587,6 +2596,7 @@ void MaterialDataTest::accessLayerOutOfBounds() {
     data.findAttributeId(2, MaterialAttribute::AlphaMask);
     data.attributeId(2, "AlphaMask");
     data.attributeId(2, MaterialAttribute::AlphaMask);
+    data.attributeData(2, 0);
     data.attributeName(2, 0);
     data.attributeType(2, 0);
     data.attributeType(2, "AlphaMask");
@@ -2626,6 +2636,7 @@ void MaterialDataTest::accessLayerOutOfBounds() {
         "Trade::MaterialData::findAttributeId(): index 2 out of range for 2 layers\n"
         "Trade::MaterialData::attributeId(): index 2 out of range for 2 layers\n"
         "Trade::MaterialData::attributeId(): index 2 out of range for 2 layers\n"
+        "Trade::MaterialData::attributeData(): index 2 out of range for 2 layers\n"
         "Trade::MaterialData::attributeName(): index 2 out of range for 2 layers\n"
         "Trade::MaterialData::attributeType(): index 2 out of range for 2 layers\n"
         "Trade::MaterialData::attributeType(): index 2 out of range for 2 layers\n"
@@ -2844,6 +2855,7 @@ void MaterialDataTest::accessOutOfBoundsInLayerIndex() {
 
     std::ostringstream out;
     Error redirectError{&out};
+    data.attributeData(1, 2);
     data.attributeName(1, 2);
     data.attributeType(1, 2);
     data.attribute(1, 2);
@@ -2853,6 +2865,7 @@ void MaterialDataTest::accessOutOfBoundsInLayerIndex() {
     data.mutableAttribute<Int>(1, 2);
     data.mutableAttribute<Containers::MutableStringView>(1, 2);
     CORRADE_COMPARE(out.str(),
+        "Trade::MaterialData::attributeData(): index 2 out of range for 2 attributes in layer 1\n"
         "Trade::MaterialData::attributeName(): index 2 out of range for 2 attributes in layer 1\n"
         "Trade::MaterialData::attributeType(): index 2 out of range for 2 attributes in layer 1\n"
         "Trade::MaterialData::attribute(): index 2 out of range for 2 attributes in layer 1\n"