Fix softmax_rgb_blend() when mesh is outside zfar

Summary:
This fixes two small issues with blending.py:softmax_rgb_blend():
  1) zfar and znear attributes are propagated from the camera settings instead of just using default settings of znear=1.0 and zfar=100.0
  2) A check is added to prevent arithmetic overflow in softmax_rgb_blend()

This is a fix in response to https://github.com/facebookresearch/pytorch3d/issues/334
where meshes rendererd using a SoftPhongShader with faces_per_pixel=1 appear black.  This only occurs when the scale of the mesh is large (vertex values > 100, where 100 is the default value of zfar).  This fix allows the caller to increase the value of cameras.zfar to match the scale of her/his mesh.

Reviewed By: nikhilaravi

Differential Revision: D23517541

fbshipit-source-id: ab8631ce9e5f2149f140b67b13eff857771b8807

pytorch3d/renderer/blending.py

@@ -186,7 +186,7 @@ def softmax_rgb_blend(
     z_inv = (zfar - fragments.zbuf) / (zfar - znear) * mask
     # pyre-fixme[16]: `Tuple` has no attribute `values`.
     # pyre-fixme[6]: Expected `Tensor` for 1st param but got `float`.
-    z_inv_max = torch.max(z_inv, dim=-1).values[..., None]
+    z_inv_max = torch.max(z_inv, dim=-1).values[..., None].clamp(min=eps)
     # pyre-fixme[6]: Expected `Tensor` for 1st param but got `float`.
     weights_num = prob_map * torch.exp((z_inv - z_inv_max) / blend_params.gamma)
 

pytorch3d/renderer/mesh/shader.py

@@ -117,7 +117,11 @@ class SoftPhongShader(nn.Module):
             cameras=cameras,
             materials=materials,
         )
-        images = softmax_rgb_blend(colors, fragments, blend_params)
+        znear = kwargs.get("znear", getattr(cameras, "znear", 1.0))
+        zfar = kwargs.get("zfar", getattr(cameras, "zfar", 100.0))
+        images = softmax_rgb_blend(
+            colors, fragments, blend_params, znear=znear, zfar=zfar
+        )
         return images
 
 
@@ -214,7 +218,11 @@ class SoftGouraudShader(nn.Module):
             cameras=cameras,
             materials=materials,
         )
-        images = softmax_rgb_blend(pixel_colors, fragments, self.blend_params)
+        znear = kwargs.get("znear", getattr(cameras, "znear", 1.0))
+        zfar = kwargs.get("zfar", getattr(cameras, "zfar", 100.0))
+        images = softmax_rgb_blend(
+            pixel_colors, fragments, self.blend_params, znear=znear, zfar=zfar
+        )
         return images
 
 

tests/test_render_meshes.py

@@ -30,6 +30,7 @@ from pytorch3d.renderer.mesh.shader import (
     HardFlatShader,
     HardGouraudShader,
     HardPhongShader,
+    SoftPhongShader,
     SoftSilhouetteShader,
     TexturedSoftPhongShader,
 )
@@ -981,3 +982,63 @@ class TestRenderMeshes(TestCaseMixin, unittest.TestCase):
             )
 
         self.assertClose(rgb, image_ref, atol=0.05)
+
+    def test_simple_sphere_outside_zfar(self):
+        """
+        Test output when rendering a sphere that is beyond zfar with a SoftPhongShader.
+        This renders a sphere of radius 500, with the camera at x=1500 for different
+        settings of zfar.  This is intended to check 1) setting cameras.zfar propagates
+        to the blender and that the rendered sphere is (soft) clipped if it is beyond
+        zfar, 2) make sure there are no numerical precision/overflow errors associated
+        with larger world coordinates
+        """
+        device = torch.device("cuda:0")
+
+        # Init mesh
+        sphere_mesh = ico_sphere(5, device)
+        verts_padded = sphere_mesh.verts_padded() * 500
+        faces_padded = sphere_mesh.faces_padded()
+        feats = torch.ones_like(verts_padded, device=device)
+        textures = TexturesVertex(verts_features=feats)
+        sphere_mesh = Meshes(verts=verts_padded, faces=faces_padded, textures=textures)
+
+        R, T = look_at_view_transform(1500, 0.0, 0.0)
+
+        # Init shader settings
+        materials = Materials(device=device)
+        lights = PointLights(device=device)
+        lights.location = torch.tensor([0.0, 0.0, +1000.0], device=device)[None]
+
+        raster_settings = RasterizationSettings(
+            image_size=256, blur_radius=0.0, faces_per_pixel=1
+        )
+        for zfar in (10000.0, 100.0):
+            cameras = FoVPerspectiveCameras(
+                device=device, R=R, T=T, aspect_ratio=1.0, fov=60.0, zfar=zfar
+            )
+            rasterizer = MeshRasterizer(
+                cameras=cameras, raster_settings=raster_settings
+            )
+            blend_params = BlendParams(1e-4, 1e-4, (0, 0, 1.0))
+
+            shader = SoftPhongShader(
+                lights=lights,
+                cameras=cameras,
+                materials=materials,
+                blend_params=blend_params,
+            )
+            renderer = MeshRenderer(rasterizer=rasterizer, shader=shader)
+            images = renderer(sphere_mesh)
+            rgb = images[0, ..., :3].squeeze().cpu()
+
+            filename = "test_simple_sphere_outside_zfar_%d.png" % int(zfar)
+
+            # Load reference image
+            image_ref = load_rgb_image(filename, DATA_DIR)
+
+            if DEBUG:
+                Image.fromarray((rgb.numpy() * 255).astype(np.uint8)).save(
+                    DATA_DIR / ("DEBUG_" + filename)
+                )
+
+            self.assertClose(rgb, image_ref, atol=0.05)