python: have a common header with Python format string definitions.

To not have to duplicate these for each and every case, enlarging the
surface for potential bugs. Also changing the signatures to number +
identifier, instead of identifier repeated number of times. Means the
compiler won't be able to deduplicate / overlap the literals in the
binary, but is much more maintainable.

For Numpy this causes the slices to be reported as actual typed Numpy
arrays instead of typeless tuples, which is good I guess? Not sure why
that wasn't the case before, or what is the difference, and how it will
behave for sparse types such as aligned matrices.

doc/python/magnum.trade.rst

@@ -112,7 +112,7 @@
         >>> list(mesh.attribute(trade.MeshAttribute.POSITION))[:3]
         [Vector(-1, -1, 1), Vector(1, -1, 1), Vector(1, 1, 1)]
         >>> np.array(mesh.attribute(trade.MeshAttribute.NORMAL), copy=False)[2]
-        (0., 0., 1.)
+        array([0., 0., 1.], dtype=float32)
 
     Depending on the value of :ref:`index_data_flags` / :ref:`vertex_data_flags`
     it's also possible to access the data in a mutable way via

src/Magnum/CMakeLists.txt

@@ -70,8 +70,11 @@ configure_file(${CMAKE_CURRENT_SOURCE_DIR}/versionBindings.h.cmake
 install(FILES ${CMAKE_CURRENT_BINARY_DIR}/versionBindings.h DESTINATION ${MAGNUM_INCLUDE_INSTALL_DIR})
 
 if(MAGNUM_WITH_PYTHON)
-    add_custom_target(MagnumPython SOURCES PythonBindings.h)
+    set(MagnumPython_SRCS
-    install(FILES PythonBindings.h DESTINATION ${MAGNUM_INCLUDE_INSTALL_DIR})
+        PythonBindings.h
+        StridedArrayViewPythonBindings.h)
+    add_custom_target(MagnumPython SOURCES ${MagnumPython_SRCS})
+    install(FILES ${MagnumPython_SRCS} DESTINATION ${MAGNUM_INCLUDE_INSTALL_DIR})
 endif()
 
 find_package(Magnum COMPONENTS GL SceneGraph)

src/Magnum/StridedArrayViewPythonBindings.h

@@ -0,0 +1,70 @@
+#ifndef Magnum_StridedArrayViewPythonBindings_h
+#define Magnum_StridedArrayViewPythonBindings_h
+/*
+    This file is part of Magnum.
+
+    Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019,
+                2020, 2021, 2022 Vladimír Vondruš <mosra@centrum.cz>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+*/
+
+#include <Corrade/Containers/StridedArrayViewPythonBindings.h>
+#include <Magnum/Magnum.h>
+
+namespace Corrade { namespace Containers { namespace Implementation {
+
+/* This expands Containers::Implementation::pythonFormatString() with Magnum
+   types. Using e.g. "3f" instead of "fff" as that makes Numpy understand even
+   the slices as arrays in a concrete type (or it at least repr()s them as
+   such), with "fff" it gives back an untyped tuple. */
+
+#define _c(type, string)                                                    \
+    template<> constexpr const char* pythonFormatString<Magnum::type>() { return string; }
+_c(Vector2,     "2f")
+_c(Vector2d,    "2d")
+_c(Vector2ub,   "2B")
+_c(Vector2b,    "2b")
+_c(Vector2us,   "2H")
+_c(Vector2s,    "2h")
+_c(Vector2ui,   "2I")
+_c(Vector2i,    "2i")
+_c(Vector3,     "3f")
+_c(Vector3d,    "3d")
+_c(Vector3ub,   "3B")
+_c(Vector3b,    "3b")
+_c(Vector3us,   "3H")
+_c(Vector3s,    "3h")
+_c(Vector3ui,   "3I")
+_c(Vector3i,    "3i")
+_c(Vector4,     "4f")
+_c(Vector4d,    "4d")
+_c(Vector4ub,   "4B")
+_c(Vector4b,    "4b")
+_c(Vector4us,   "4H")
+_c(Vector4s,    "4h")
+_c(Vector4ui,   "4I")
+_c(Vector4i,    "4i")
+#undef _c
+
+}
+
+}}
+
+#endif

src/python/magnum/test/test_trade.py

@@ -322,7 +322,7 @@ class MeshData(unittest.TestCase):
         positions = mesh.attribute(position_id)
         self.assertEqual(positions.size, (3, ))
         self.assertEqual(positions.stride, (28, ))
-        self.assertEqual(positions.format, 'fff')
+        self.assertEqual(positions.format, '3f')
         self.assertEqual(list(positions), [
             Vector3(-1, -1, 0.25),
             Vector3(0, 1, 0.5),
@@ -348,7 +348,7 @@ class MeshData(unittest.TestCase):
         mutable_positions = mesh.mutable_attribute(position_id)
         self.assertEqual(mutable_positions.size, (3, ))
         self.assertEqual(mutable_positions.stride, (28, ))
-        self.assertEqual(mutable_positions.format, 'fff')
+        self.assertEqual(mutable_positions.format, '3f')
         self.assertEqual(list(mutable_positions), [
             Vector3(-1, -1, 0.25),
             Vector3(0, 1, 0.5),

src/python/magnum/trade.cpp

@@ -40,8 +40,8 @@
 
 #include "Corrade/Containers/PythonBindings.h"
 #include "Corrade/Containers/OptionalPythonBindings.h"
-#include "Corrade/Containers/StridedArrayViewPythonBindings.h"
 #include "Magnum/PythonBindings.h"
+#include "Magnum/StridedArrayViewPythonBindings.h"
 
 #include "corrade/EnumOperators.h"
 #include "corrade/pluginmanager.h"
@@ -447,9 +447,9 @@ template<class T, bool(Trade::AbstractSceneConverter::*f)(const T&, Containers::
 
 Containers::Triple<const char*, py::object(*)(const char*), void(*)(char*, py::handle)> accessorsForMeshIndexType(const MeshIndexType type) {
     switch(type) {
-        #define _c(type, string)                                            \
+        #define _c(type)                                                    \
             case MeshIndexType::type: return {                              \
-                string,                                                     \
+                Containers::Implementation::pythonFormatString<type>(),     \
                 [](const char* item) {                                      \
                     return py::cast(*reinterpret_cast<const type*>(item));  \
                 },                                                          \
@@ -457,9 +457,9 @@ Containers::Triple<const char*, py::object(*)(const char*), void(*)(char*, py::h
                     *reinterpret_cast<type*>(item) = py::cast<type>(object); \
                 }};
         /* LCOV_EXCL_START */
-        _c(UnsignedByte, "B")
+        _c(UnsignedByte)
-        _c(UnsignedShort, "H")
+        _c(UnsignedShort)
-        _c(UnsignedInt, "I")
+        _c(UnsignedInt)
         /* LCOV_EXCL_STOP */
         #undef _c
     }
@@ -469,9 +469,9 @@ Containers::Triple<const char*, py::object(*)(const char*), void(*)(char*, py::h
 
 Containers::Triple<const char*, py::object(*)(const char*), void(*)(char*, py::handle)> accessorsForVertexFormat(const VertexFormat format) {
     switch(format) {
-        #define _c(format, string)                                          \
+        #define _c(format)                                                  \
             case VertexFormat::format: return {                             \
-                string,                                                     \
+                Containers::Implementation::pythonFormatString<format>(),   \
                 [](const char* item) {                                      \
                     return py::cast(*reinterpret_cast<const format*>(item)); \
                 },                                                          \
@@ -480,9 +480,9 @@ Containers::Triple<const char*, py::object(*)(const char*), void(*)(char*, py::h
                 }};
         /* Types (such as half-floats) that need to be cast before passed
            from/to pybind that doesn't understand the type directly */
-        #define _cc(format, castType, string)                               \
+        #define _cc(format, castType)                                       \
             case VertexFormat::format: return {                             \
-                string,                                                     \
+                Containers::Implementation::pythonFormatString<format>(),   \
                 [](const char* item) {                                      \
                     return py::cast(castType(*reinterpret_cast<const format*>(item))); \
                 },                                                          \
@@ -490,41 +490,41 @@ Containers::Triple<const char*, py::object(*)(const char*), void(*)(char*, py::h
                     *reinterpret_cast<format*>(item) = format(py::cast<castType>(object)); \
                 }};
         /* LCOV_EXCL_START */
-        _c(Float,                   "f")
+        _c(Float)
-        _c(Double,                  "d")
+        _c(Double)
-        _c(UnsignedByte,            "B")
+        _c(UnsignedByte)
-        _c(Byte,                    "b")
+        _c(Byte)
-        _c(UnsignedShort,           "H")
+        _c(UnsignedShort)
-        _c(Short,                   "h")
+        _c(Short)
-        _c(UnsignedInt,             "I")
+        _c(UnsignedInt)
-        _c(Int,                     "i")
+        _c(Int)
-
+
-        _c(Vector2,                 "ff")
+        _c(Vector2)
-        _c(Vector2d,                "dd")
+        _c(Vector2d)
-        _cc(Vector2ub, Vector2ui,   "BB")
+        _cc(Vector2ub, Vector2ui)
-        _cc(Vector2b, Vector2i,     "bb")
+        _cc(Vector2b, Vector2i)
-        _cc(Vector2us, Vector2ui,   "HH")
+        _cc(Vector2us, Vector2ui)
-        _cc(Vector2s, Vector2i,     "hh")
+        _cc(Vector2s, Vector2i)
-        _c(Vector2ui,               "II")
+        _c(Vector2ui)
-        _c(Vector2i,                "ii")
+        _c(Vector2i)
-
+
-        _c(Vector3,                 "fff")
+        _c(Vector3)
-        _c(Vector3d,                "ddd")
+        _c(Vector3d)
-        _cc(Vector3ub, Vector3ui,   "BBB")
+        _cc(Vector3ub, Vector3ui)
-        _cc(Vector3b, Vector3i,     "bbb")
+        _cc(Vector3b, Vector3i)
-        _cc(Vector3us, Vector3ui,   "HHH")
+        _cc(Vector3us, Vector3ui)
-        _cc(Vector3s, Vector3i,     "hhh")
+        _cc(Vector3s, Vector3i)
-        _c(Vector3ui,               "III")
+        _c(Vector3ui)
-        _c(Vector3i,                "iii")
+        _c(Vector3i)
-
+
-        _c(Vector4,                 "ffff")
+        _c(Vector4)
-        _c(Vector4d,                "dddd")
+        _c(Vector4d)
-        _cc(Vector4ub, Vector4ui,   "BBBB")
+        _cc(Vector4ub, Vector4ui)
-        _cc(Vector4b, Vector4i,     "bbbb")
+        _cc(Vector4b, Vector4i)
-        _cc(Vector4us, Vector4ui,   "HHHH")
+        _cc(Vector4us, Vector4ui)
-        _cc(Vector4s, Vector4i,     "hhhh")
+        _cc(Vector4s, Vector4i)
-        _c(Vector4ui,               "IIII")
+        _c(Vector4ui)
-        _c(Vector4i,                "iiii")
+        _c(Vector4i)
         /* LCOV_EXCL_STOP */
         #undef _c
         #undef _cc