python: use writeonly properties for shader uniform setters.

This practically means we depend on pybind11 2.3 now.

src/python/magnum/shaders.cpp

@@ -54,11 +54,7 @@ template<UnsignedInt dimensions> void vertexColor(NonDestructibleBase<Shaders::V
 
         /* Using lambdas to avoid method chaining getting into signatures */
 
-        // TODO: make writeonly once https://github.com/pybind/pybind11/pull/1144
-        // is released
-        .def_property("transformation_projection_matrix", [](Shaders::VertexColor<dimensions>&) {
-            return MatrixTypeFor<dimensions, Float>{};
-        }, &Shaders::VertexColor<dimensions>::setTransformationProjectionMatrix,
+        .def_property("transformation_projection_matrix", nullptr, &Shaders::VertexColor<dimensions>::setTransformationProjectionMatrix,
             "Transformation and projection matrix");
 }
 
@@ -127,33 +123,27 @@ void shaders(py::module& m) {
             }, "Flags")
             .def_property_readonly("light_count", &Shaders::Phong::lightCount,
                 "Light count")
-            // TODO: make write-only once https://github.com/pybind/pybind11/pull/1144
-            // is released
-            .def_property("ambient_color", [](Shaders::Phong&) { return Color4{}; },
+            .def_property("ambient_color", nullptr,
                 &Shaders::Phong::setAmbientColor, "Ambient color")
-            .def_property("diffuse_color", [](Shaders::Phong&) { return Color4{}; },
+            .def_property("diffuse_color", nullptr,
                 &Shaders::Phong::setDiffuseColor, "Diffuse color")
-            .def_property("specular_color", [](Shaders::Phong&) { return Color4{}; },
+            .def_property("specular_color", nullptr,
                 &Shaders::Phong::setSpecularColor, "Specular color")
             // TODO: textures, once exposed
-            .def_property("shininess", [](Shaders::Phong&) { return Float{}; },
+            .def_property("shininess", nullptr,
                 &Shaders::Phong::setShininess, "Shininess")
-            .def_property("alpha_mask", [](Shaders::Phong&) { return Float{}; },
+            .def_property("alpha_mask", nullptr,
                 &Shaders::Phong::setAlphaMask, "Alpha mask")
-            .def_property("transformation_matrix", [](Shaders::Phong&) { return Matrix4{}; },
+            .def_property("transformation_matrix", nullptr,
                 &Shaders::Phong::setTransformationMatrix, "Set transformation matrix")
-            .def_property("normal_matrix", [](Shaders::Phong&) { return Matrix3x3{}; },
+            .def_property("normal_matrix", nullptr,
                 &Shaders::Phong::setNormalMatrix, "Set normal matrix")
-            .def_property("projection_matrix", [](Shaders::Phong&) { return Matrix4{}; },
+            .def_property("projection_matrix", nullptr,
                 &Shaders::Phong::setProjectionMatrix, "Set projection matrix")
-            .def_property("light_positions", [](Shaders::Phong&) {
-                return std::vector<Vector3>{};
-            }, [](Shaders::Phong& self, const std::vector<Vector3>& positions) {
+            .def_property("light_positions", nullptr, [](Shaders::Phong& self, const std::vector<Vector3>& positions) {
                 self.setLightPositions(positions);
             }, "Light positions")
-            .def_property("light_colors", [](Shaders::Phong&) {
-                return std::vector<Color4>{};
-            }, [](Shaders::Phong& self, const std::vector<Color4>& colors) {
+            .def_property("light_colors", nullptr, [](Shaders::Phong& self, const std::vector<Color4>& colors) {
                 self.setLightColors(colors);
             }, "Light colors");
     }