Primitives: document how to scale capsule / cylinder to preserve normals.

src/Magnum/Primitives/Capsule.h

@@ -81,6 +81,12 @@ class MAGNUM_PRIMITIVES_EXPORT Capsule3D {
          * Indexed @ref MeshPrimitive::Triangles with normals and optional 2D
          * texture coordinates. If texture coordinates are generated, vertices
          * of one segment are duplicated for texture wrapping.
+         *
+         * The capsule is by default created with radius set to @cpp 1.0f @ce.
+         * In order to get radius @f$ r @f$, length @f$ l @f$ and preserve
+         * correct normals, set @p halfLength to @f$ 0.5 \frac{l}{r} @f$ and
+         * then scale all @ref Trade::MeshData3D::positions() by @f$ r @f$, for
+         * example using @ref MeshTools::transformPointsInPlace().
          */
         static Trade::MeshData3D solid(UnsignedInt hemisphereRings, UnsignedInt cylinderRings, UnsignedInt segments, Float halfLength, TextureCoords textureCoords = TextureCoords::DontGenerate);
 

src/Magnum/Primitives/Cylinder.h

@@ -74,6 +74,12 @@ class MAGNUM_PRIMITIVES_EXPORT Cylinder {
          * texture coordinates and optional capped ends. If texture coordinates
          * are generated, vertices of one segment are duplicated for texture
          * wrapping.
+         *
+         * The cylinder is by default created with radius set to @cpp 1.0f @ce.
+         * In order to get radius @f$ r @f$, length @f$ l @f$ and preserve
+         * correct normals, set @p halfLength to @f$ 0.5 \frac{l}{r} @f$ and
+         * then scale all @ref Trade::MeshData3D::positions() by @f$ r @f$, for
+         * example using @ref MeshTools::transformPointsInPlace().
          */
         static Trade::MeshData3D solid(UnsignedInt rings, UnsignedInt segments, Float halfLength, Flags flags = Flags());