[gui] Add get_view_matrix() and get_projection_matrix() APIs for camera

python/taichi/ui/camera.py

@@ -175,6 +175,28 @@ def z_far(self, z_far):
         """
         self.ptr.z_far(z_far)
 
+    def get_view_matrix(self):
+        """Get the view matrix(in row major) of the camera.
+
+        Example::
+
+            >>> camera.get_view_matrix()
+        """
+        return self.ptr.get_view_matrix()
+
+    def get_projection_matrix(self, aspect):
+        """Get the projection matrix(in row major) of the camera.
+
+        Args:
+            aspect (:mod:`taichi.types.primitive_types`): \
+                aspect ratio of the camera
+
+        Example::
+
+            >>> camera.get_projection_matrix(1080/720)
+        """
+        return self.ptr.get_projection_matrix(aspect)
+
     def track_user_inputs(self,
                           window,
                           movement_speed=1.0,

taichi/python/export_ggui.cpp

@@ -1,6 +1,7 @@
 
 #include <vector>
 #include "pybind11/pybind11.h"
+#include <pybind11/numpy.h>
 #include "pybind11/stl.h"
 
 #include "taichi/common/interface.h"
@@ -34,6 +35,21 @@ pybind11::tuple vec3_to_tuple(glm::vec3 v) {
   return pybind11::make_tuple(v.x, v.y, v.z);
 }
 
+// Here we convert the 2d-array to numpy array using pybind. Refs:
+// https://pybind11.readthedocs.io/en/stable/advanced/pycpp/numpy.html?highlight=array_t#vectorizing-functions
+// https://stackoverflow.com/questions/44659924/returning-numpy-arrays-via-pybind11
+py::array_t<float> mat4_to_nparray(glm::mat4 mat) {
+  // Here we must explicitly pass args using py::detail::any_container<ssize_t>.
+  // Refs:
+  // https://stackoverflow.com/questions/54055530/error-no-matching-function-for-call-to-pybind11buffer-infobuffer-info
+  return py::array_t<float>(
+      py::detail::any_container<ssize_t>({4, 4}),  // shape (rows, cols)
+      py::detail::any_container<ssize_t>(
+          {sizeof(float) * 4, sizeof(float)}),  // strides in bytes
+      glm::value_ptr(mat),                      // buffer pointer
+      nullptr);
+}
+
 struct PyGui {
   GuiBase *gui;  // not owned
   void begin(std::string name, float x, float y, float width, float height) {
@@ -99,6 +115,12 @@ struct PyCamera {
   void z_far(float z_far_) {
     camera.z_far = z_far_;
   }
+  py::array_t<float> get_view_matrix() {
+    return mat4_to_nparray(camera.get_view_matrix());
+  }
+  py::array_t<float> get_projection_matrix(float aspect_ratio) {
+    return mat4_to_nparray(camera.get_projection_matrix(aspect_ratio));
+  }
 };
 
 struct PyScene {
@@ -368,7 +390,9 @@ void export_ggui(py::module &m) {
       .def("top", &PyCamera::top)
       .def("bottom", &PyCamera::bottom)
       .def("z_near", &PyCamera::z_near)
-      .def("z_far", &PyCamera::z_far);
+      .def("z_far", &PyCamera::z_far)
+      .def("get_view_matrix", &PyCamera::get_view_matrix)
+      .def("get_projection_matrix", &PyCamera::get_projection_matrix);
 
   py::class_<Event>(m, "Event")
       .def_property("key", &Event::get_key, &Event::set_key);

tests/python/test_ggui.py

@@ -296,3 +296,26 @@ def render():
 @test_utils.test(arch=supported_archs)
 def test_exit_without_showing():
     window = ti.ui.Window("Taichi", (256, 256), show_window=False)
+
+
+@test_utils.test(arch=supported_archs)
+def test_get_camera_view_and_projection_matrix():
+    scene = ti.ui.Scene()
+    camera = ti.ui.make_camera()
+    camera.position(0, 0, 3)
+    camera.lookat(0, 0, 0)
+
+    scene.set_camera(camera)
+
+    view_matrix = camera.get_view_matrix()
+    projection_matrix = camera.get_projection_matrix(1080 / 720)
+
+    for i in range(4):
+        assert (abs(view_matrix[i, i] - 1) <= 1e-5)
+    assert (abs(view_matrix[3, 2] + 3) <= 1e-5)
+
+    assert (abs(projection_matrix[0, 0] - 1.6094756) <= 1e-5)
+    assert (abs(projection_matrix[1, 1] - 2.4142134) <= 1e-5)
+    assert (abs(projection_matrix[2, 2] - 1.0001000e-4) <= 1e-5)
+    assert (abs(projection_matrix[2, 3] + 1.0000000) <= 1e-5)
+    assert (abs(projection_matrix[3, 2] - 1.0001000e-1) <= 1e-5)