[Feat] Render lidar before agents and allow for tuple as color (#115)

* Render lidar before agent, so agent is on top. Adding get render_color function to lidar like in Agent.render so it allows for alpha in colors.

* now it is ray and not the circle

* added alpha instead of tuple including alpha

* Update vmas/simulator/sensors.py

Co-authored-by: Matteo Bettini <55539777+matteobettini@users.noreply.github.com>

* Update vmas/simulator/sensors.py

Co-authored-by: Matteo Bettini <55539777+matteobettini@users.noreply.github.com>

* Update vmas/simulator/sensors.py

* Update vmas/simulator/sensors.py

---------

Co-authored-by: Matteo Bettini <55539777+matteobettini@users.noreply.github.com>

Author: Zartris

vmas/simulator/sensors.py

@@ -6,12 +6,12 @@
 
 import typing
 from abc import ABC, abstractmethod
-from typing import Callable, List, Union
+from typing import Callable, List, Tuple, Union
 
 import torch
 
 import vmas.simulator.core
-import vmas.simulator.utils
+from vmas.simulator.utils import Color
 
 if typing.TYPE_CHECKING:
     from vmas.simulator.rendering import Geom
@@ -52,7 +52,8 @@ def __init__(
         n_rays: int = 8,
         max_range: float = 1.0,
         entity_filter: Callable[[vmas.simulator.core.Entity], bool] = lambda _: True,
-        render_color: vmas.simulator.utils.Color = vmas.simulator.utils.Color.GRAY,
+        render_color: Union[Color, Tuple[float, float, float]] = Color.GRAY,
+        alpha: float = 1.0,
         render: bool = True,
     ):
         super().__init__(world)
@@ -71,6 +72,7 @@ def __init__(
         self._render = render
         self._entity_filter = entity_filter
         self._render_color = render_color
+        self._alpha = alpha
 
     def to(self, device: torch.device):
         self._angles = self._angles.to(device)
@@ -85,6 +87,16 @@ def entity_filter(
     ):
         self._entity_filter = entity_filter
 
+    @property
+    def render_color(self):
+        if isinstance(self._render_color, Color):
+            return self._render_color.value
+        return self._render_color
+
+    @property
+    def alpha(self):
+        return self._alpha
+
     def measure(self):
         dists = []
         for angle in self._angles.unbind(1):
@@ -123,9 +135,10 @@ def render(self, env_index: int = 0) -> "List[Geom]":
                 xform.set_translation(*self.agent.state.pos[env_index])
                 xform.set_rotation(angle)
                 ray.add_attr(xform)
+                ray.set_color(r=0, g=0, b=0, alpha=self.alpha)
 
                 ray_circ = rendering.make_circle(0.01)
-                ray_circ.set_color(*self._render_color.value)
+                ray_circ.set_color(*self.render_color, alpha=self.alpha)
                 xform = rendering.Transform()
                 rot = torch.stack([torch.cos(angle), torch.sin(angle)], dim=-1)
                 pos_circ = (