diff --git a/example/example.mk b/example/example.mk
index 9f4bfe1..ba58f52 100644
--- a/example/example.mk
+++ b/example/example.mk
@@ -542,3 +542,14 @@ SIERPINSKI_OBJ = \
 
 example/sierpinski.elf: LDSCRIPT = $(LIB)/main.lds
 example/sierpinski.elf: $(START_OBJ) $(SIERPINSKI_OBJ)
+
+TETRAHEDRON_OBJ = \
+	example/tetrahedron.o \
+	holly/core.o \
+	holly/region_array.o \
+	holly/background.o \
+	holly/ta_fifo_polygon_converter.o \
+	holly/video_output.o
+
+example/tetrahedron.elf: LDSCRIPT = $(LIB)/main.lds
+example/tetrahedron.elf: $(START_OBJ) $(TETRAHEDRON_OBJ)
diff --git a/example/icosphere.cpp b/example/icosphere.cpp
index 88867fe..648378b 100644
--- a/example/icosphere.cpp
+++ b/example/icosphere.cpp
@@ -92,7 +92,7 @@ void transform(ta_parameter_writer& parameter,
       auto l = lights[0] - point;
       auto n_dot_l = dot(n, l);
       if (n_dot_l > 0) {
-        color.x += 0.6 * n_dot_l / (length(n) * length(l));
+        color.x += 0.6 * n_dot_l / (magnitude(n) * magnitude(l));
       }
     }
 
@@ -100,7 +100,7 @@ void transform(ta_parameter_writer& parameter,
       auto l = lights[1] - point;
       auto n_dot_l = dot(n, l);
       if (n_dot_l > 0) {
-        color.y += 0.6 * n_dot_l / (length(n) * length(l));
+        color.y += 0.6 * n_dot_l / (magnitude(n) * magnitude(l));
       }
     }
 
@@ -108,7 +108,7 @@ void transform(ta_parameter_writer& parameter,
       auto l = lights[2] - point;
       auto n_dot_l = dot(n, l);
       if (n_dot_l > 0) {
-        color.z += 0.6 * n_dot_l / (length(n) * length(l));
+        color.z += 0.6 * n_dot_l / (magnitude(n) * magnitude(l));
       }
     }
 
diff --git a/example/tetrahedron.cpp b/example/tetrahedron.cpp
new file mode 100644
index 0000000..b26485f
--- /dev/null
+++ b/example/tetrahedron.cpp
@@ -0,0 +1,198 @@
+#include <cstdint>
+
+#include "holly/texture_memory_alloc.hpp"
+#include "holly/holly.hpp"
+#include "holly/core.hpp"
+#include "holly/core_bits.hpp"
+#include "holly/ta_fifo_polygon_converter.hpp"
+#include "holly/ta_parameter.hpp"
+#include "holly/ta_global_parameter.hpp"
+#include "holly/ta_vertex_parameter.hpp"
+#include "holly/ta_bits.hpp"
+#include "holly/isp_tsp.hpp"
+#include "holly/region_array.hpp"
+#include "holly/background.hpp"
+#include "holly/video_output.hpp"
+#include "memorymap.hpp"
+
+#include "sh7091/store_queue.hpp"
+
+#include "math/vec3.hpp"
+
+constexpr float isqrt2 = 0.7071067811865475;
+
+using vec3 = vec<3, float>;
+
+void triangle(vec3 a, vec3 b, vec3 c, const uint32_t base_color)
+{
+  const uint32_t parameter_control_word = para_control::para_type::polygon_or_modifier_volume
+                                        | para_control::list_type::opaque
+                                        | obj_control::col_type::packed_color;
+
+  const uint32_t isp_tsp_instruction_word = isp_tsp_instruction_word::depth_compare_mode::greater
+                                          | isp_tsp_instruction_word::culling_mode::no_culling;
+
+  const uint32_t tsp_instruction_word = tsp_instruction_word::src_alpha_instr::one
+                                      | tsp_instruction_word::dst_alpha_instr::zero
+                                      | tsp_instruction_word::fog_control::no_fog;
+
+  *reinterpret_cast<ta_global_parameter::polygon_type_0 *>(store_queue) =
+    ta_global_parameter::polygon_type_0(parameter_control_word,
+                                        isp_tsp_instruction_word,
+					tsp_instruction_word,
+                                        0, // texture_control_word
+                                        0, // data_size_for_sort_dma
+                                        0  // next_address_for_sort_dma
+                                        );
+  sq_transfer_32byte(ta_fifo_polygon_converter);
+
+  *reinterpret_cast<ta_vertex_parameter::polygon_type_0 *>(store_queue) =
+    ta_vertex_parameter::polygon_type_0(polygon_vertex_parameter_control_word(false),
+					a.x, a.y, a.z,
+					base_color);
+  sq_transfer_32byte(ta_fifo_polygon_converter);
+
+  *reinterpret_cast<ta_vertex_parameter::polygon_type_0 *>(store_queue) =
+    ta_vertex_parameter::polygon_type_0(polygon_vertex_parameter_control_word(false),
+					b.x, b.y, b.z,
+					base_color);
+  sq_transfer_32byte(ta_fifo_polygon_converter);
+
+  *reinterpret_cast<ta_vertex_parameter::polygon_type_0 *>(store_queue) =
+    ta_vertex_parameter::polygon_type_0(polygon_vertex_parameter_control_word(true),
+					c.x, c.y, c.z,
+					base_color);
+  sq_transfer_32byte(ta_fifo_polygon_converter);
+}
+
+void tetrahedron(vec3 a, vec3 b, vec3 c, vec3 d)
+{
+  /*
+    vec3 a = { 1, 0,-isqrt2};
+    vec3 b = {-1, 0,-isqrt2};
+    vec3 c = { 0, 1, isqrt2};
+    vec3 d = { 0,-1, isqrt2};
+
+      c - d
+     / \ /
+    b - a
+  */
+
+  triangle(a, b, c, 0xff'00ffff); // c
+  triangle(a, c, d, 0xff'ffff00); // y
+  triangle(d, a, b, 0xff'ff00ff); // m
+  triangle(d, b, c, 0xff'00ff00); // g
+}
+
+vec3 midpoint(vec3 a, vec3 b)
+{
+  return {(a.x + b.x) / 2.f,
+	  (a.y + b.y) / 2.f,
+	  (a.z + b.z) / 2.f};
+}
+
+void subdivide(vec3 a, vec3 b, vec3 c, vec3 d, int depth)
+{
+  vec3 ab = midpoint(a, b);
+  vec3 ac = midpoint(a, c);
+  vec3 ad = midpoint(a, d);
+  vec3 bc = midpoint(b, c);
+  vec3 bd = midpoint(b, d);
+  vec3 cd = midpoint(c, d);
+
+  if (depth == 0) {
+    tetrahedron(ad,  a, ab, ac);
+    tetrahedron(bd, ab,  b, bc);
+    tetrahedron(cd, ac, bc,  c);
+    tetrahedron( d, ad, bd, cd);
+  } else {
+    subdivide(ad,  a, ab, ac, depth - 1);
+    subdivide(bd, ab,  b, bc, depth - 1);
+    subdivide(cd, ac, bc,  c, depth - 1);
+    subdivide( d, ad, bd, cd, depth - 1);
+  }
+}
+
+float theta;
+
+vec3 transform(vec3 v)
+{
+  float x1 = v.x * __builtin_cosf(theta) - v.z * __builtin_sinf(theta);
+  float y1 = v.y;
+  float z1 = v.x * __builtin_sinf(theta) + v.z * __builtin_cosf(theta);
+
+  float x = x1;
+  float y = y1 * __builtin_cosf(-theta * 0.3) - z1 * __builtin_sinf(-theta * 0.3);
+  float z = y1 * __builtin_sinf(-theta * 0.3) + z1 * __builtin_cosf(-theta * 0.3);
+
+  return {
+    x * 200.f + 320.f,
+    y * 200.f + 240.f,
+    1.f / (z + 10.f),
+  };
+}
+
+void main()
+{
+  video_output::set_mode_vga();
+  theta = 0.f;
+
+  constexpr uint32_t ta_alloc = ta_alloc_ctrl::pt_opb::no_list
+                              | ta_alloc_ctrl::tm_opb::no_list
+                              | ta_alloc_ctrl::t_opb::no_list
+                              | ta_alloc_ctrl::om_opb::_16x4byte
+                              | ta_alloc_ctrl::o_opb::_16x4byte;
+
+  constexpr struct opb_size opb_size = { .opaque = 16 * 4
+                                       , .opaque_modifier = 16 * 4
+                                       , .translucent = 0
+                                       , .translucent_modifier = 0
+                                       , .punch_through = 0
+                                       };
+
+  holly.SOFTRESET = softreset::pipeline_soft_reset
+                  | softreset::ta_soft_reset;
+  holly.SOFTRESET = 0;
+
+  core_init();
+  region_array2(640 / 32, 480 / 32, opb_size);
+  background_parameter(0xff0000ff);
+
+  uint32_t frame_ix = 0;
+
+  while (true) {
+    ta_polygon_converter_init(opb_size.total(),
+                              ta_alloc,
+                              640 / 32,
+                              480 / 32);
+
+    vec3 a = { 1, 0,-isqrt2};
+    vec3 b = {-1, 0,-isqrt2};
+    vec3 c = { 0, 1, isqrt2};
+    vec3 d = { 0,-1, isqrt2};
+
+    subdivide(transform(a),
+	      transform(b),
+	      transform(c),
+	      transform(d),
+	      4);
+
+    theta += 0.01f;
+
+    // end of opaque list
+    *reinterpret_cast<ta_global_parameter::end_of_list *>(store_queue) =
+      ta_global_parameter::end_of_list(para_control::para_type::end_of_list);
+    sq_transfer_32byte(ta_fifo_polygon_converter);
+
+    ta_wait_opaque_list();
+
+    core_start_render(frame_ix);
+    core_wait_end_of_render_video();
+
+    while (!spg_status::vsync(holly.SPG_STATUS));
+    core_flip(frame_ix);
+    while (spg_status::vsync(holly.SPG_STATUS));
+
+    frame_ix = (frame_ix + 1) & 1;
+  }
+}