Fix rendering energy loss in RenderEngineVtk

Energy loss is due to three issues.

1. Drake introduced an erroneous patch which bled energy badly.
2. Set the skybox to use gamma correction, even for hdr images.
3. Introduce a *new* patch to change the VTK brdf model from a single-scatter
   approximation to a multi-scatter approximation.

This will have an immediate change on rendered outputs -- images will be
brighter.

Based on brightness changes:
  1. The lighting configuration tutorial has been updated accordingly.
  2. The unit tests for RenderEngineVtk have had reference values (subject
     to PBR) brightened accordingly.

Current camera configurations will need to be updated, especially with
respect to their exposure values and lighting levels. Renderings for which
high exposure values seemed necessary will now seem oversaturated.
Furthermore, with more energy coming from the environment map, lights may
need to be brighter to have a comparable effect as before.

TODO:
- Push my model and my env map so it can be downloaded via curl.
- Submit PR with instructions on how to reproduce with the given files.

Author: SeanCurtis-TRI

geometry/render_vtk/internal_render_engine_vtk.cc

@@ -952,8 +952,7 @@ void RenderEngineVtk::InitializePipelines() {
       // environment map.
       skybox->SetFloorRight(0, -1, 0);
       skybox->SetProjection(vtkSkybox::Sphere);
-      // Linear color space (aka *not HDR*) requires gamma correction.
-      skybox->SetGammaCorrect(!env_map.is_hdr);
+      skybox->GammaCorrectOn();
       renderer->AddActor(skybox);
     }
     // Setting an environment map should require all materials to be PBR.

geometry/render_vtk/test/internal_render_engine_vtk_test.cc

@@ -2099,34 +2099,34 @@ TEST_F(RenderEngineVtkTest, EnvironmentMap) {
       {.description = "Facing +Wz, toward the blue face, magenta behind; HDR",
        .R_WC = RotationMatrixd(),
        .bg_color = Rgba(0, 0, 1),
-       .sphere_color = Rgba(0.61176471, 0.38039216, 0.56470588),  // magenta-ish
+       .sphere_color = Rgba(0.97254902, 0.62352941, 0.89411765),  // magenta-ish
        .map_path = hdr_path},
       {.description = "Facing blue; testing the skybox",
        .R_WC = RotationMatrixd(),
        .bg_color = Rgba(0, 0, 1),
-       .sphere_color = Rgba(0.61176471, 0.38039216, 0.56470588),  // magenta-ish
+       .sphere_color = Rgba(0.97254902, 0.62352941, 0.89411765),  // magenta-ish
        .map_path = hdr_path,
        .show_map = false},
       {.description = "Facing blue; testing the clone",
        .R_WC = RotationMatrixd(),
        .bg_color = Rgba(0, 0, 1),
-       .sphere_color = Rgba(0.61176471, 0.38039216, 0.56470588),  // magenta-ish
+       .sphere_color = Rgba(0.97254902, 0.62352941, 0.89411765),  // magenta-ish
        .map_path = hdr_path,
        .render_clone = true},
       {.description = "Facing +Wy, toward the green face, yellow behind; HDR",
        .R_WC = RotationMatrixd::MakeXRotation(M_PI / 2),
        .bg_color = Rgba(0, 1, 0),
-       .sphere_color = Rgba(0.60784314, 0.56470588, 0.38039216),  // yellow-ish
+       .sphere_color = Rgba(0.96862745, 0.89411765, 0.62352941),  // yellow-ish
        .map_path = hdr_path},
       {.description = "Facing +Wx, toward the red face, cyan behind; HDR",
        .R_WC = RotationMatrixd::MakeYRotation(M_PI / 2),
        .bg_color = Rgba(1, 0, 0),
-       .sphere_color = Rgba(0.30980392, 0.60392157, 0.60392157),  // cyan-ish
+       .sphere_color = Rgba(0.50980392, 0.96470588, 0.96470588),  // cyan-ish
        .map_path = hdr_path},
       {.description = "Facing +Wz, toward the blue face, magenta behind; LDR",
        .R_WC = RotationMatrixd(),
        .bg_color = Rgba(0.0588, 0.0588, 0.9255),
-       .sphere_color = Rgba(0.45098039, 0.25490196, 0.39607843),  // magenta-ish
+       .sphere_color = Rgba(0.71372549, 0.41960784, 0.61960784),  // magenta-ish
        .map_path = ldr_path},
   };
 

geometry/render_vtk/test/whole_image_custom_color.png

@@ -0,0 +1,31 @@
+The single scattering algorithm originally implemented is known to create
+rendering artfacts (dark, rough metals and dielectrics with overly bright
+fresnel reflections). This patch replaces the single-scatter model with a more
+modern multi-scatter approximation. (See change for reference to source.)
+
+--- Rendering/OpenGL2/vtkOpenGLPolyDataMapper.cxx
++++ Rendering/OpenGL2/vtkOpenGLPolyDataMapper.cxx
+@@ -1417,12 +1417,17 @@ void vtkOpenGLPolyDataMapper::ReplaceShaderLight(
+     toString.clear();
+     toString.str("");
+ 
+-    toString << "  // In IBL, we assume that v=n, so the amount of light reflected is\n"
+-                "  // the reflectance F0\n"
+-                "  vec3 specularBrdf = F0 * brdf.r + F90 * brdf.g;\n"
+-                "  vec3 iblSpecular = prefilteredSpecularColor * specularBrdf;\n"
+-                // no diffuse for metals
+-                "  vec3 iblDiffuse = (1.0 - F0) * (1.0 - metallic) * irradiance * albedo;\n"
++    toString << "  // Multi-scatter approximation: see https://bruop.github.io/ibl/\n"
++                "  diffuse = (1.0 - metallic) * (1.0 - 0.04) * albedo;\n"
++                "  vec3 Fr = max(vec3(1 - roughness), F0) - F0;\n"
++                "  vec3 k_S = F0 + Fr * pow(1.0 - NdV, 5.0);\n"
++                "  vec3 FssEss = k_S * brdf.r + F90 * brdf.g;\n"
++                "  float Ems = 1.0 - (brdf.r + brdf.g);\n"
++                "  vec3 F_avg = F0 + (1.0 - F0) / 21.0;\n"
++                "  vec3 FmsEms = Ems * FssEss * F_avg / (1.0 - F_avg * Ems);\n"
++                "  vec3 k_D = diffuse * (1.0 - FssEss - FmsEms);\n"
++                "  vec3 iblSpecular = FssEss * prefilteredSpecularColor;\n"
++                "  vec3 iblDiffuse = (FmsEms + k_D) * irradiance;\n"
+                 "  vec3 color = iblDiffuse + iblSpecular;\n"
+                 "\n";
+ 

tools/workspace/vtk_internal/patches/upstream/add_multi_scattering_to_pbr.patch

@@ -192,9 +192,9 @@ def vtk_internal_repository(
             # - Patch file names should begin with the name of the module being
             #   edited (e.g., patching IO/Image is named io_image_{foo}.patch).
             # - Use alphabetical order within a directory when listing patches.
+            ":patches/upstream/add_multi_scattering_to_pbr.patch",
             ":patches/upstream/common_core_rm_iostream.patch",
             ":patches/upstream/rendering_core_vtkcomposite_exception.patch",
-            ":patches/upstream/rendering_opengl2_scaled_albedo_for_ibl.patch",
             ":patches/upstream/utilities_x11_more_functions.patch",
             ":patches/common_core_fmt12.patch",
             ":patches/common_core_fmt9.patch",

tools/workspace/vtk_internal/patches/upstream/rendering_opengl2_scaled_albedo_for_ibl.patch

@@ -1692,7 +1692,10 @@
     "\n",
     "# Center on the balls, filling the frame.\n",
     "comparator.pose_camera_once(camera_in_world=[0, -3.5, 2],\n",
-    "                            target_in_world=[0, 0, 2])"
+    "                            target_in_world=[0, 0, 2])\n",
+    "\n",
+    "# Restore Meshcat exposure levels.\n",
+    "meshcat.SetProperty(\"/Render Settings/<object>\", \"exposure\", 1)"
    ]
   },
   {
@@ -2457,6 +2460,7 @@
     "env = RenderEngineSpec(\n",
     "    \"Iteration 1\",\n",
     "    {\n",
+    "        \"exposure\": 2,\n",
     "        \"lights\": [\n",
     "               LightParameter(type=\"directional\", frame=\"world\", direction=[0, 1, 0], intensity=10),\n",
     "        ],\n",
@@ -2491,6 +2495,7 @@
     "env = RenderEngineSpec(\n",
     "    \"Iteration 2\",\n",
     "    {\n",
+    "        \"exposure\": 2,\n",
     "        \"lights\": [\n",
     "               LightParameter(type=\"directional\", frame=\"world\", direction=[0, 1, -.5], intensity=10),\n",
     "        ],\n",
@@ -2522,6 +2527,7 @@
     "env = RenderEngineSpec(\n",
     "    \"Iteration 3\",\n",
     "    {\n",
+    "        \"exposure\": 2,\n",
     "        \"cast_shadows\": True,\n",
     "        \"lights\": [\n",
     "               LightParameter(type=\"directional\", frame=\"world\", direction=[0, 1, -.5], intensity=10),\n",
@@ -2555,6 +2561,7 @@
     "    \"Iteration 4\",\n",
     "    {\n",
     "        \"environment_map\": EnvironmentMap(texture=EquirectangularMap(path=hdr_path)),\n",
+    "        \"exposure\": 2,\n",
     "        \"cast_shadows\": True,\n",
     "        \"lights\": [\n",
     "               LightParameter(type=\"directional\", frame=\"world\", direction=[0, 1, -.5], intensity=10),\n",
@@ -2582,15 +2589,18 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "# Final configuration: Tone down the window light; we only want faint shadows from the window.\n",
+    "# Final configuration: Correct two things:\n",
+    "#  1. The shadows are more pronounced than we want. Dim the light to reduce the strength of the shadow.\n",
+    "#  2. The exposure value was set based *only* on the environment map. Adding the window light has made the scene\n",
+    "#     over exposed. Reduce the exposure to return back to the desired levels.\n",
     "env = RenderEngineSpec(\n",
     "    \"Iteration 5\",\n",
     "    {\n",
     "        \"environment_map\": EnvironmentMap(texture=EquirectangularMap(path=hdr_path)),\n",
     "        \"cast_shadows\": True,\n",
-    "        \"exposure\": 3,\n",
+    "        \"exposure\": 1.5,\n",
     "        \"lights\": [\n",
-    "               LightParameter(type=\"directional\", frame=\"world\", direction=[0, 1, -.5], intensity=1),\n",
+    "               LightParameter(type=\"directional\", frame=\"world\", direction=[0, 1, -.5], intensity=3.5),\n",
     "        ],\n",
     "    }\n",
     ")\n",
@@ -2631,14 +2641,13 @@
     "   \"environment_map\": EnvironmentMap(texture=EquirectangularMap(path=hdr_path)),\n",
     "    \"cast_shadows\": True,\n",
     "    \"shadow_map_size\": 1024,\n",
-    "    # With additional lights, we reduce exposure.\n",
-    "    \"exposure\": 2,\n",
+    "    \"exposure\": 1, # more lights --> reduced exposure.\n",
     "    \"lights\": [\n",
     "               LightParameter(**(ceiling_light | {\"position\": [-1, 1, 3.0]})),\n",
     "               LightParameter(**(ceiling_light | {\"position\": [-1, -1, 3.0]})),\n",
     "               LightParameter(**(ceiling_light | {\"position\": [1, 1, 3.0]})),\n",
     "               LightParameter(**(ceiling_light | {\"position\": [1, -1, 3.0]})),\n",
-    "               LightParameter(type=\"directional\", frame=\"world\", direction=[0, 1, -.5], intensity=1),\n",
+    "               LightParameter(type=\"directional\", frame=\"world\", direction=[0, 1, -.5], intensity=5),\n",
     "              ],\n",
     "}\n",
     "env = RenderEngineSpec(\"Full Lighting\", render_config)\n",