new tests demonstrating pixel matching

Summary: Demonstrate current behavior of pixels with new tests of all renderers.

Reviewed By: gkioxari

Differential Revision: D32651141

fbshipit-source-id: 3ca30b4274ed2699bc5e1a9c6437eb3f0b738cbf

tests/test_camera_pixels.py

+# Copyright (c) Facebook, Inc. and its affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+import unittest
+
+import torch
+from common_testing import TestCaseMixin
+from pytorch3d.renderer import (
+    MeshRasterizer,
+    NDCGridRaysampler,
+    PerspectiveCameras,
+    PointsRasterizationSettings,
+    PointsRasterizer,
+    PulsarPointsRenderer,
+    RasterizationSettings,
+)
+from pytorch3d.structures import Meshes, Pointclouds
+
+
+"""
+PyTorch3D renderers operate in an align_corners=False manner.
+This file demonstrates the pixel-perfect calculation by very simple
+examples.
+"""
+
+
+class _CommonData:
+    """
+    Contains data for all these tests.
+
+    - Firstly, a non-square at the origin specified in ndc space and
+    screen space. Principal point is in the center of the image.
+    Focal length is 1.0 in world space.
+    This camera has the identity as its world to view transformation, so
+    it is facing down the positive z axis with y being up and x being left.
+    A point on the z=1.0 focal plane has its x,y world coordinate equal to
+    its NDC.
+
+    - Secondly, batched together with that, is a camera with the same
+    focal length facing in the same direction but located so that it faces
+    the corner of the corner pixel of the first image, with its principal
+    point located at its corner, so that it maps the z=1 plane to NDC just
+    like the first.
+
+    - a single point self.point in world space which is located on a plane 1.0
+    in front from the camera which is located exactly in the center
+    of a known pixel (self.x, self.y), specifically with negative x and slightly
+    positive y, so it is in the top right quadrant of the image.
+
+    - A second batch of cameras defined in screen space which exactly match the
+    first ones.
+
+    So that this data can be copied for making demos, it is easiest to leave
+    it as a freestanding class.
+    """
+
+    def __init__(self):
+        self.H, self.W = 249, 125
+        self.image_size = (self.H, self.W)
+        self.camera_ndc = PerspectiveCameras(
+            focal_length=1.0,
+            image_size=(self.image_size,),
+            in_ndc=True,
+            T=torch.tensor([[0.0, 0.0, 0.0], [-1.0, self.H / self.W, 0.0]]),
+            principal_point=((-0.0, -0.0), (1.0, -self.H / self.W)),
+        )
+        # Note how principal point is  specifiied
+        self.camera_screen = PerspectiveCameras(
+            focal_length=self.W / 2.0,
+            principal_point=((self.W / 2.0, self.H / 2.0), (0.0, self.H)),
+            image_size=(self.image_size,),
+            T=torch.tensor([[0.0, 0.0, 0.0], [-1.0, self.H / self.W, 0.0]]),
+            in_ndc=False,
+        )
+
+        # 81 is more than half of 125, 113 is a bit less than half of 249
+        self.x, self.y = 81, 113
+        self.point = [-0.304, 0.176, 1]
+        # The point is in the center of pixel (81, 113)
+        # where pixel (0,0) is the top left.
+        # 81 is 38/2 pixels over the midpoint (125-1)/2=62
+        # and 38/125=0.304
+        # 113 is 22/2 pixels under the midpoint (249-1)/2=124
+        # and 22/125=0.176
+
+
+class TestPixels(TestCaseMixin, unittest.TestCase):
+    def test_mesh(self):
+        data = _CommonData()
+        # Three points on the plane at unit 1 from the camera in
+        # world space, whose mean is the known point.
+        verts = torch.tensor(
+            [[-0.288, 0.192, 1], [-0.32, 0.192, 1], [-0.304, 0.144, 1]]
+        )
+        self.assertClose(verts.mean(0), torch.tensor(data.point))
+        faces = torch.LongTensor([[0, 1, 2]])
+        # A mesh of one triangular face whose centroid is the known point
+        # duplicated so it can be rendered from two cameras.
+        meshes = Meshes(verts=[verts], faces=[faces]).extend(2)
+        faces_per_pixel = 2
+        for camera in (data.camera_ndc, data.camera_screen):
+            rasterizer = MeshRasterizer(
+                cameras=camera,
+                raster_settings=RasterizationSettings(
+                    image_size=data.image_size, faces_per_pixel=faces_per_pixel
+                ),
+            )
+            barycentric_coords_found = rasterizer(meshes).bary_coords
+            self.assertTupleEqual(
+                barycentric_coords_found.shape,
+                (2,) + data.image_size + (faces_per_pixel, 3),
+            )
+            # We see that the barycentric coordinates at the expected
+            # pixel are (1/3, 1/3, 1/3), indicating that this pixel
+            # hits the centroid of the triangle.
+            self.assertClose(
+                barycentric_coords_found[:, data.y, data.x, 0],
+                torch.full((2, 3), 1 / 3.0),
+                atol=1e-5,
+            )
+
+    def test_pointcloud(self):
+        data = _CommonData()
+        clouds = Pointclouds(points=torch.tensor([[data.point]])).extend(2)
+        colorful_cloud = Pointclouds(
+            points=torch.tensor([[data.point]]), features=torch.ones(1, 1, 3)
+        ).extend(2)
+        points_per_pixel = 2
+        # for camera in [data.camera_screen]:
+        for camera in (data.camera_ndc, data.camera_screen):
+            rasterizer = PointsRasterizer(
+                cameras=camera,
+                raster_settings=PointsRasterizationSettings(
+                    image_size=data.image_size,
+                    radius=0.0001,
+                    points_per_pixel=points_per_pixel,
+                ),
+            )
+            # when rasterizing we expect only one pixel to be occupied
+            rasterizer_output = rasterizer(clouds).idx
+            self.assertTupleEqual(
+                rasterizer_output.shape, (2,) + data.image_size + (points_per_pixel,)
+            )
+            found = torch.nonzero(rasterizer_output != -1)
+            self.assertTupleEqual(found.shape, (2, 4))
+            self.assertListEqual(found[0].tolist(), [0, data.y, data.x, 0])
+            self.assertListEqual(found[1].tolist(), [1, data.y, data.x, 0])
+
+            if camera.in_ndc():
+                # Pulsar not currently working in screen space.
+                pulsar_renderer = PulsarPointsRenderer(rasterizer=rasterizer)
+                pulsar_output = pulsar_renderer(
+                    colorful_cloud, gamma=(0.1, 0.1), znear=(0.1, 0.1), zfar=(70, 70)
+                )
+                self.assertTupleEqual(
+                    pulsar_output.shape, (2,) + data.image_size + (3,)
+                )
+                # Look for points rendered in the red channel only, expecting our one.
+                # Check the first batch element only.
+                # TODO: Something is odd with the second.
+                found = torch.nonzero(pulsar_output[0, :, :, 0])
+                self.assertTupleEqual(found.shape, (1, 2))
+                self.assertListEqual(found[0].tolist(), [data.y, data.x])
+                # Should be:
+                # found = torch.nonzero(pulsar_output[:, :, :, 0])
+                # self.assertTupleEqual(found.shape, (2, 3))
+                # self.assertListEqual(found[0].tolist(), [0, data.y, data.x])
+                # self.assertListEqual(found[1].tolist(), [1, data.y, data.x])
+
+    def test_raysampler(self):
+        data = _CommonData()
+        gridsampler = NDCGridRaysampler(
+            image_width=data.W,
+            image_height=data.H,
+            n_pts_per_ray=2,
+            min_depth=1.0,
+            max_depth=2.0,
+        )
+        for camera in (data.camera_ndc, data.camera_screen):
+            bundle = gridsampler(camera)
+            self.assertTupleEqual(bundle.xys.shape, (2,) + data.image_size + (2,))
+            self.assertTupleEqual(
+                bundle.directions.shape, (2,) + data.image_size + (3,)
+            )
+            self.assertClose(
+                bundle.xys[:, data.y, data.x],
+                torch.tensor(data.point[:2]).expand(2, -1),
+            )
+            # We check only the first batch element.
+            # Second element varies because of camera location.
+            self.assertClose(
+                bundle.directions[0, data.y, data.x],
+                torch.tensor(data.point),
+            )
+
+    def test_camera(self):
+        data = _CommonData()
+        # Our point, plus the image center, and a corner of the image.
+        # Located at the focal-length distance away
+        points = torch.tensor([data.point, [0, 0, 1], [1, data.H / data.W, 1]])
+        for cameras in (data.camera_ndc, data.camera_screen):
+            ndc_points = cameras.transform_points_ndc(points)
+            screen_points = cameras.transform_points_screen(points)
+            camera_points = cameras.transform_points(points)
+            for batch_idx in range(2):
+                # NDC space agrees with the original
+                self.assertClose(ndc_points[batch_idx], points, atol=1e-5)
+                # First point in screen space is the center of our expected pixel
+                self.assertClose(
+                    screen_points[batch_idx][0],
+                    torch.tensor([data.x + 0.5, data.y + 0.5, 1.0]),
+                    atol=1e-5,
+                )
+                # Second point in screen space is the center of the screen
+                self.assertClose(
+                    screen_points[batch_idx][1],
+                    torch.tensor([data.W / 2.0, data.H / 2.0, 1.0]),
+                    atol=1e-5,
+                )
+                # Third point in screen space is the corner of the screen
+                # (corner of corner pixels)
+                self.assertClose(
+                    screen_points[batch_idx][2],
+                    torch.tensor([0.0, 0.0, 1.0]),
+                    atol=1e-5,
+                )
+
+                if cameras.in_ndc():
+                    self.assertClose(camera_points[batch_idx], ndc_points[batch_idx])
+                else:
+                    # transform_points does something strange for screen cameras
+                    if batch_idx == 0:
+                        wanted = torch.stack(
+                            [
+                                data.W - screen_points[batch_idx, :, 0],
+                                data.H - screen_points[batch_idx, :, 1],
+                                torch.ones(3),
+                            ],
+                            dim=1,
+                        )
+                    else:
+                        wanted = torch.stack(
+                            [
+                                -screen_points[batch_idx, :, 0],
+                                2 * data.H - screen_points[batch_idx, :, 1],
+                                torch.ones(3),
+                            ],
+                            dim=1,
+                        )
+
+                    print(wanted)
+                    print(camera_points[batch_idx])
+                    self.assertClose(camera_points[batch_idx], wanted)