Trade: added MeshData::attributeId().

Useful for quick localization of named attribs when dealing with
attributeData() (for example in MeshTools).

src/Magnum/Trade/MeshData.cpp

@@ -261,6 +261,12 @@ UnsignedInt MeshData::attributeFor(const MeshAttribute name, UnsignedInt id) con
     #endif
 }
 
+UnsignedInt MeshData::attributeId(const MeshAttribute name, UnsignedInt id) const {
+    const UnsignedInt attributeId = attributeFor(name, id);
+    CORRADE_ASSERT(attributeId != ~UnsignedInt{}, "Trade::MeshData::attributeId(): index" << id << "out of range for" << attributeCount(name) << name << "attributes", {});
+    return attributeId;
+}
+
 VertexFormat MeshData::attributeFormat(MeshAttribute name, UnsignedInt id) const {
     const UnsignedInt attributeId = attributeFor(name, id);
     CORRADE_ASSERT(attributeId != ~UnsignedInt{}, "Trade::MeshData::attributeFormat(): index" << id << "out of range for" << attributeCount(name) << name << "attributes", {});

src/Magnum/Trade/MeshData.h

@@ -817,6 +817,14 @@ class MAGNUM_TRADE_EXPORT MeshData {
          */
         UnsignedInt attributeCount(MeshAttribute name) const;
 
+        /**
+         * @brief Absolute ID of a named attribute
+         *
+         * The @p id is expected to be smaller than
+         * @ref attributeCount(MeshAttribute) const.
+         */
+        UnsignedInt attributeId(MeshAttribute name, UnsignedInt id = 0) const;
+
         /**
          * @brief Format of a named attribute
          *
@@ -1129,6 +1137,7 @@ class MAGNUM_TRADE_EXPORT MeshData {
            implementations. */
         friend AbstractImporter;
 
+        /* Internal helper that doesn't assert, unlike attributeId() */
         UnsignedInt attributeFor(MeshAttribute name, UnsignedInt id) const;
 
         UnsignedInt _vertexCount;

src/Magnum/Trade/Test/MeshDataTest.cpp

@@ -628,6 +628,11 @@ void MeshDataTest::construct() {
     CORRADE_COMPARE(data.attributeCount(meshAttributeCustom(13)), 1);
     CORRADE_COMPARE(data.attributeCount(MeshAttribute::Color), 0);
     CORRADE_COMPARE(data.attributeCount(meshAttributeCustom(23)), 0);
+    CORRADE_COMPARE(data.attributeId(MeshAttribute::Position), 0);
+    CORRADE_COMPARE(data.attributeId(MeshAttribute::Normal), 2);
+    CORRADE_COMPARE(data.attributeId(MeshAttribute::TextureCoordinates), 1);
+    CORRADE_COMPARE(data.attributeId(MeshAttribute::TextureCoordinates, 1), 3);
+    CORRADE_COMPARE(data.attributeId(meshAttributeCustom(13)), 4);
     CORRADE_COMPARE(data.attributeFormat(MeshAttribute::Position),
         VertexFormat::Vector3);
     CORRADE_COMPARE(data.attributeFormat(MeshAttribute::Normal),
@@ -1533,6 +1538,8 @@ void MeshDataTest::attributeNotFound() {
     data.attributeStride(2);
     data.attribute(2);
     data.attribute<Vector2>(2);
+    data.attributeId(MeshAttribute::Position);
+    data.attributeId(MeshAttribute::Color, 2);
     data.attributeFormat(MeshAttribute::Position);
     data.attributeFormat(MeshAttribute::Color, 2);
     data.attributeOffset(MeshAttribute::Position);
@@ -1555,6 +1562,8 @@ void MeshDataTest::attributeNotFound() {
         "Trade::MeshData::attributeStride(): index 2 out of range for 2 attributes\n"
         "Trade::MeshData::attribute(): index 2 out of range for 2 attributes\n"
         "Trade::MeshData::attribute(): index 2 out of range for 2 attributes\n"
+        "Trade::MeshData::attributeId(): index 0 out of range for 0 Trade::MeshAttribute::Position attributes\n"
+        "Trade::MeshData::attributeId(): index 2 out of range for 2 Trade::MeshAttribute::Color attributes\n"
         "Trade::MeshData::attributeFormat(): index 0 out of range for 0 Trade::MeshAttribute::Position attributes\n"
         "Trade::MeshData::attributeFormat(): index 2 out of range for 2 Trade::MeshAttribute::Color attributes\n"
         "Trade::MeshData::attributeOffset(): index 0 out of range for 0 Trade::MeshAttribute::Position attributes\n"