Point light attenuation/falloff does not work when cast_shadows is enabled

[azeey]

Environment

• OS Version: Ubuntu 20.04
• Source or binary build? source, ign-rendering6, f043b4fc
• Render Engine: ogre2

Description

• Expected behavior: Point light attenuation/falloff to work regardless of cast_shadows.
• Actual behavior: When cast_shadow is enabled, the light does not falloff according to the attenuation parameters. For example, given the following light source

<light type="point" name="mylight">
  <cast_shadows>true</cast_shadows>
  <pose>0 0 2.5 0 0 0</pose>
  <diffuse>0.8 0.8 0.8 1</diffuse>
  <specular>0.8 0.8 0.8 1</specular>
  <direction>0 0 -1</direction>
  <intensity>2</intensity>
  <attenuation>
    <range>4</range>
    <linear>0.5</linear>
    <constant>0.2</constant>
    <quadratic>0.01</quadratic>
  </attenuation>
</light>

with cast_shadows = true, I get a sharp circle determined by the range (4m) of the light.

with cast_shadows = false, the light falls of smoothly, but the box does not have a shadow.

Steps to reproduce

1. Run the attached file (test.sdf.txt) in ign gazebo.
2. Change <cast_shadows> to true or false.