MeshTools: added generateTrivialIndices().

Because writing a for loop for this is annoying, and using std::iota()
isn't any better either.

doc/changelog.dox

@@ -291,6 +291,8 @@ See also:
 -   New @ref MeshTools::boundingSphereBouncingBubble() algorithm for
     calculating a tight bounding sphere for a mesh, along with a trivial
     @ref MeshTools::boundingRange() for AABBs (see [mosra/magnum#557](https://github.com/mosra/magnum/pull/557))
+-   Added @ref MeshTools::generateTrivialIndices() as a STL-less alternative
+    to @ref std::iota()
 -   Added @ref MeshTools::generateQuadIndices() for quad triangulation
     including non-convex and non-planar quads
 -   New @ref MeshTools::filterAttributes(),

src/Magnum/MeshTools/GenerateIndices.cpp

@@ -84,6 +84,17 @@ UnsignedInt primitiveCount(const MeshPrimitive primitive, const UnsignedInt elem
     CORRADE_ASSERT_UNREACHABLE("MeshTools::primitiveCount(): invalid primitive" << primitive, {});
 }
 
+void generateTrivialIndicesInto(const Containers::StridedArrayView1D<UnsignedInt>& output) {
+    for(std::size_t i = 0; i != output.size(); ++i)
+        output[i] = i;
+}
+
+Containers::Array<UnsignedInt> generateTrivialIndices(const UnsignedInt vertexCount) {
+    Containers::Array<UnsignedInt> output{NoInit, vertexCount};
+    generateTrivialIndicesInto(output);
+    return output;
+}
+
 void generateLineStripIndicesInto(const UnsignedInt vertexCount, const Containers::StridedArrayView1D<UnsignedInt>& output) {
     CORRADE_ASSERT(vertexCount == 0 || vertexCount >= 2,
         "MeshTools::generateLineStripIndicesInto(): expected either zero or at least two vertices, got" << vertexCount, );

src/Magnum/MeshTools/GenerateIndices.h

@@ -26,7 +26,7 @@
 */
 
 /** @file
- * @brief Function @ref Magnum::MeshTools::primitiveCount(), @ref Magnum::MeshTools::generateLineStripIndices(), @ref Magnum::MeshTools::generateLineStripIndicesInto(), @ref Magnum::MeshTools::generateLineLoopIndices(), @ref Magnum::MeshTools::generateLineLoopIndicesInto(), @ref Magnum::MeshTools::generateTriangleStripIndices(), @ref Magnum::MeshTools::generateTriangleStripIndicesInto(), @ref Magnum::MeshTools::generateTriangleFanIndices(), @ref Magnum::MeshTools::generateTriangleFanIndicesInto(), @ref Magnum::MeshTools::generateIndices()
+ * @brief Function @ref Magnum::MeshTools::primitiveCount(), @ref Magnum::MeshTools::generateTrivialIndices(), @ref Magnum::MeshTools::generateTrivialIndicesInto(), @ref Magnum::MeshTools::generateLineStripIndices(), @ref Magnum::MeshTools::generateLineStripIndicesInto(), @ref Magnum::MeshTools::generateLineLoopIndices(), @ref Magnum::MeshTools::generateLineLoopIndicesInto(), @ref Magnum::MeshTools::generateTriangleStripIndices(), @ref Magnum::MeshTools::generateTriangleStripIndicesInto(), @ref Magnum::MeshTools::generateTriangleFanIndices(), @ref Magnum::MeshTools::generateTriangleFanIndicesInto(), @ref Magnum::MeshTools::generateIndices()
  * @m_since{2020,06}
  */
 
@@ -49,6 +49,27 @@ is either zero or at least @cpp 2 @ce for a line-based primitive and at least
 */
 MAGNUM_MESHTOOLS_EXPORT UnsignedInt primitiveCount(MeshPrimitive primitive, UnsignedInt elementCount);
 
+/**
+@brief Create a trivial index buffer
+@m_since_latest
+
+Generates a @cpp 0, 1, 2, 3, 4, 5, ... @ce sequence, i.e. what @ref std::iota()
+would produce. Can be used to turn a non-indexed mesh into indexed.
+@see @ref generateTrivialIndicesInto(), @ref generateLineStripIndices(),
+    @ref generateLineLoopIndices(), @ref generateTriangleStripIndices(),
+    @ref generateTriangleFanIndices(), @ref generateIndices()
+*/
+MAGNUM_MESHTOOLS_EXPORT Containers::Array<UnsignedInt> generateTrivialIndices(UnsignedInt vertexCount);
+
+/**
+@brief Create a trivial index buffer into an existing array
+@m_since_latest
+
+A variant of @ref generateTrivialIndices() that fills existing memory
+instead of allocating a new array.
+*/
+MAGNUM_MESHTOOLS_EXPORT void generateTrivialIndicesInto(const Containers::StridedArrayView1D<UnsignedInt>& output);
+
 /**
 @brief Create index buffer for a line strip primitive
 @m_since{2020,06}
@@ -61,7 +82,7 @@ Primitive restart is not supported. If the mesh is already indexed, use
 and overloads instead.
 @see @ref generateLineStripIndicesInto(), @ref generateLineLoopIndices(),
     @ref generateTriangleStripIndices(), @ref generateTriangleFanIndices(),
-    @ref generateIndices()
+    @ref generateTrivialIndices(), @ref generateIndices()
 */
 MAGNUM_MESHTOOLS_EXPORT Containers::Array<UnsignedInt> generateLineStripIndices(UnsignedInt vertexCount);
 
@@ -153,7 +174,7 @@ Primitive restart is not supported. If the mesh is already indexed, use
 and overloads instead.
 @see @ref generateLineLoopIndicesInto(), @ref generateLineStripIndices(),
     @ref generateTriangleStripIndices(), @ref generateTriangleFanIndices(),
-    @ref generateIndices()
+    @ref generateTrivialIndices(), @ref generateIndices()
 */
 MAGNUM_MESHTOOLS_EXPORT Containers::Array<UnsignedInt> generateLineLoopIndices(UnsignedInt vertexCount);
 
@@ -246,7 +267,7 @@ mesh is already indexed, use @ref generateTriangleStripIndices(const Containers:
 and overloads instead.
 @see @ref generateTriangleStripIndicesInto(), @ref generateLineStripIndices(),
     @ref generateLineLoopIndices(), @ref generateTriangleFanIndices(),
-    @ref generateIndices()
+    @ref generateTrivialIndices(), @ref generateIndices()
 */
 MAGNUM_MESHTOOLS_EXPORT Containers::Array<UnsignedInt> generateTriangleStripIndices(UnsignedInt vertexCount);
 
@@ -339,7 +360,7 @@ mesh is already indexed, use @ref generateTriangleFanIndices(const Containers::S
 and overloads instead.
 @see @ref generateTriangleFanIndicesInto(), @ref generateLineStripIndices(),
     @ref generateLineLoopIndices(), @ref generateTriangleStripIndices(),
-    @ref generateIndices()
+    @ref generateTrivialIndices(), @ref generateIndices()
 */
 MAGNUM_MESHTOOLS_EXPORT Containers::Array<UnsignedInt> generateTriangleFanIndices(UnsignedInt vertexCount);
 

src/Magnum/MeshTools/Test/GenerateIndicesTest.cpp

@@ -45,6 +45,8 @@ struct GenerateIndicesTest: TestSuite::Tester {
     void primitiveCountInvalidVertexCount();
     void primitiveCountInvalidPrimitive();
 
+    void generateTrivialIndices();
+
     void generateLineStripIndices();
     template<class T> void generateLineStripIndicesIndexed();
     template<class T> void generateLineStripIndicesIndexed2D();
@@ -212,6 +214,8 @@ GenerateIndicesTest::GenerateIndicesTest() {
               &GenerateIndicesTest::primitiveCountInvalidVertexCount,
               &GenerateIndicesTest::primitiveCountInvalidPrimitive,
 
+              &GenerateIndicesTest::generateTrivialIndices,
+
               &GenerateIndicesTest::generateLineStripIndices,
               &GenerateIndicesTest::generateLineStripIndicesIndexed<UnsignedInt>,
               &GenerateIndicesTest::generateLineStripIndicesIndexed<UnsignedShort>,
@@ -340,6 +344,19 @@ void GenerateIndicesTest::primitiveCountInvalidPrimitive() {
         "MeshTools::primitiveCount(): invalid primitive MeshPrimitive(0xdead)\n");
 }
 
+void GenerateIndicesTest::generateTrivialIndices() {
+    /* Empty input */
+    CORRADE_COMPARE_AS(MeshTools::generateTrivialIndices(0),
+        Containers::ArrayView<const UnsignedInt>{},
+        TestSuite::Compare::Container);
+
+    /* Common case */
+    CORRADE_COMPARE_AS(MeshTools::generateTrivialIndices(7),
+        Containers::arrayView<UnsignedInt>({
+            0, 1, 2, 3, 4, 5, 6
+        }), TestSuite::Compare::Container);
+}
+
 void GenerateIndicesTest::generateLineStripIndices() {
     /* Empty input */
     CORRADE_COMPARE_AS(MeshTools::generateLineStripIndices(0),