remove dataclass for python 3.6 compatibility.

Summary: Make RasterizationSettings be a NamedTuple instead of a dataclass. This makes the mesh renderer work with python 3.6.

Reviewed By: nikhilaravi

Differential Revision: D19769924

fbshipit-source-id: db839f3506dda7d3344fb8a101fa75bdf139ce39

pytorch3d/renderer/mesh/rasterizer.py

 #!/usr/bin/env python3
 # Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.
 
-
-from dataclasses import dataclass
 from typing import NamedTuple, Optional
 import torch
 import torch.nn as nn
@@ -20,14 +18,31 @@ class Fragments(NamedTuple):
 
 
 # Class to store the mesh rasterization params with defaults
-@dataclass
 class RasterizationSettings:
-    image_size: int = 256
-    blur_radius: float = 0.0
-    faces_per_pixel: int = 1
-    bin_size: Optional[int] = None
-    max_faces_per_bin: Optional[int] = None
-    perspective_correct: bool = False
+    __slots__ = [
+        "image_size",
+        "blur_radius",
+        "faces_per_pixel",
+        "bin_size",
+        "max_faces_per_bin",
+        "perspective_correct",
+    ]
+
+    def __init__(
+        self,
+        image_size: int = 256,
+        blur_radius: float = 0.0,
+        faces_per_pixel: int = 1,
+        bin_size: Optional[int] = None,
+        max_faces_per_bin: Optional[int] = None,
+        perspective_correct: bool = False,
+    ):
+        self.image_size = image_size
+        self.blur_radius = blur_radius
+        self.faces_per_pixel = faces_per_pixel
+        self.bin_size = bin_size
+        self.max_faces_per_bin = max_faces_per_bin
+        self.perspective_correct = perspective_correct
 
 
 class MeshRasterizer(nn.Module):