[test] [gui] Add a test of the display of wireframe mode (taichi-dev#…

…5967)

* Add a test of drawing mesh instances

* Revert "Add a test of drawing mesh instances"

This reverts commit b443eb0.

* Add a test of display of wireframe mode

* merge

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* remove unused line

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tests/python/test_ggui.py

@@ -843,3 +843,92 @@ def render():
     verify_image(window.get_image_buffer_as_numpy(),
                  'test_draw_part_of_mesh_instances')
     window.destroy()
+
+
+@pytest.mark.skipif(not _ti_core.GGUI_AVAILABLE, reason="GGUI Not Available")
+@test_utils.test(arch=supported_archs)
+def test_wireframe_mode():
+    N = 10
+    NV = (N + 1)**2
+    NT = 2 * N**2
+    NE = 2 * N * (N + 1) + N**2
+    pos = ti.Vector.field(3, ti.f32, shape=NV)
+    tri = ti.field(ti.i32, shape=3 * NT)
+    edge = ti.Vector.field(2, ti.i32, shape=NE)
+
+    @ti.kernel
+    def init_pos():
+        for i, j in ti.ndrange(N + 1, N + 1):
+            idx = i * (N + 1) + j
+            pos[idx] = ti.Vector([i / N, 1.0 - j / N, 0.5])
+
+    @ti.kernel
+    def init_tri():
+        for i, j in ti.ndrange(N, N):
+            tri_idx = 6 * (i * N + j)
+            pos_idx = i * (N + 1) + j
+            if (i + j) % 2 == 0:
+                tri[tri_idx + 0] = pos_idx
+                tri[tri_idx + 1] = pos_idx + N + 2
+                tri[tri_idx + 2] = pos_idx + 1
+                tri[tri_idx + 3] = pos_idx
+                tri[tri_idx + 4] = pos_idx + N + 1
+                tri[tri_idx + 5] = pos_idx + N + 2
+            else:
+                tri[tri_idx + 0] = pos_idx
+                tri[tri_idx + 1] = pos_idx + N + 1
+                tri[tri_idx + 2] = pos_idx + 1
+                tri[tri_idx + 3] = pos_idx + 1
+                tri[tri_idx + 4] = pos_idx + N + 1
+                tri[tri_idx + 5] = pos_idx + N + 2
+
+    @ti.kernel
+    def init_edge():
+        for i, j in ti.ndrange(N + 1, N):
+            edge_idx = i * N + j
+            pos_idx = i * (N + 1) + j
+            edge[edge_idx] = ti.Vector([pos_idx, pos_idx + 1])
+        start = N * (N + 1)
+        for i, j in ti.ndrange(N, N + 1):
+            edge_idx = start + j * N + i
+            pos_idx = i * (N + 1) + j
+            edge[edge_idx] = ti.Vector([pos_idx, pos_idx + N + 1])
+        start = 2 * N * (N + 1)
+        for i, j in ti.ndrange(N, N):
+            edge_idx = start + i * N + j
+            pos_idx = i * (N + 1) + j
+            if (i + j) % 2 == 0:
+                edge[edge_idx] = ti.Vector([pos_idx, pos_idx + N + 2])
+            else:
+                edge[edge_idx] = ti.Vector([pos_idx + 1, pos_idx + N + 1])
+
+    init_pos()
+    init_tri()
+    init_edge()
+
+    window = ti.ui.Window("test", (1024, 1024), vsync=True, show_window=False)
+    canvas = window.get_canvas()
+    scene = ti.ui.Scene()
+    camera = ti.ui.make_camera()
+    camera.position(1.5, 1, -1)
+    camera.lookat(1, 0.5, 0)
+    camera.fov(90)
+
+    def render():
+        scene.set_camera(camera)
+        scene.point_light(pos=(0.5, 1, 2), color=(1, 1, 1))
+
+        scene.mesh(pos,
+                   tri,
+                   color=(39 / 255, 123 / 255, 192 / 255),
+                   two_sided=True,
+                   show_wireframe=True)
+        canvas.scene(scene)
+
+    for _ in range(RENDER_REPEAT):
+        render()
+        window.get_image_buffer_as_numpy()
+
+    render()
+    verify_image(window.get_image_buffer_as_numpy(), 'test_wireframe_mode')
+    window.destroy()