update dispersion documentation (#9567)

* add dispersion parameter to material_sandbox

* frame_generator fixes

- fix skybox
- for baseColor to white (workaround)

* update dispersion documentation source

docs_src/README.md

@@ -49,7 +49,7 @@ to perform a number of URL replacements in addition to the copy. These replaceme
 described in [`docs_src/build/duplicates.json`].
 
 ### Core concept docs
-The primary design of Filament as a phyiscally-based renderer and details of its materials
+The primary design of Filament as a physically-based renderer and details of its materials
 system are described in `Filament.md.html` and `Materials.md.html`, respectively. These two
 documents are written in [`markdeep`]. To embed them into our book, we
  1. Convert the markdeep into html

docs_src/src_markdeep/Materials.md.html

@@ -161,7 +161,7 @@ The type and range of each property is described in table [standardPropertiesTyp
     vertex. `microThickness` represent the thickness of the thin layer of an object, and can
     generally be provided as a constant value. For example, a 1mm thin hollow sphere of radius 1m,
     would have a `thickness` of 1 and a `microThickness` of 0.001. Dispersion controls the angular
-    separation of colors transmitting through a volume, and can be set by a contant value.
+    separation of colors transmitting through a volume, and can be set by a constant value.
     Currently `thickness` and `dispersion` are not used when `refractionType` is set to `thin`.
 
 ### Base color
@@ -671,6 +671,9 @@ Water                      | 55                 | 0.36
 Crown Glass                | 59                 | 0.33
 [Table [commonMatDispersion]: Dispersion of common materials]
 
+![Figure [dispersionProperty]: `dispersion` varying from 0.0
+(left) to 5.0 (right)](images/materials/dispersion.png)
+
 ## Subsurface model
 
 ### Thickness

samples/frame_generator.cpp

@@ -333,14 +333,18 @@ static void setup(Engine* engine, View* view, Scene* scene) {
         scene->addEntity(g_light);
     }
 
+
+    // FIXME: we need a better way to set the defaults.
+    if (g_material->hasParameter("baseColor")) {
+        g_materialInstance->setParameter("baseColor", float3{ 1, 1, 1 });
+    }
+
     for (const auto& p : g_parameters) {
         g_materialInstance->setParameter(p.name.c_str(), p.start);
     }
 
-    if (!g_skyboxOn) {
-        auto ibl = FilamentApp::get().getIBL();
-        if (ibl) ibl->getSkybox()->setLayerMask(0xff, 0x00);
-    } else {
+    auto ibl = FilamentApp::get().getIBL();
+    if (!ibl || !g_skyboxOn) {
         g_skybox = Skybox::Builder().color({
                 ((g_clearColor >> 16) & 0xFF) / 255.0f,
                 ((g_clearColor >>  8) & 0xFF) / 255.0f,

samples/material_sandbox.cpp

@@ -395,6 +395,7 @@ static filament::MaterialInstance* updateInstances(
                     Color::absorptionAtDistance(color, params.distance));
             materialInstance->setParameter("ior", params.ior);
             materialInstance->setParameter("transmission", params.transmission);
+            materialInstance->setParameter("dispersion", params.dispersion);
             materialInstance->setParameter("thickness", params.thickness);
         }
     }
@@ -571,6 +572,7 @@ static void gui(filament::Engine* engine, filament::View*) {
                 if (hasRefraction) {
                     ImGui::SliderFloat("IOR", &params.ior, 1.0f, 3.0f);
                     ImGui::SliderFloat("Transmission", &params.transmission, 0.0f, 1.0f);
+                    ImGui::SliderFloat("Dispersion", &params.dispersion, 0.0f, 5.0f);
                     ImGui::SliderFloat("Thickness", &params.thickness, 0.0f, 1.0f);
                     ImGui::ColorEdit3("Transmittance", &params.transmittanceColor.r);
                     ImGui::SliderFloat("Distance", &params.distance, 0.0f, 4.0f);

samples/material_sandbox.h

@@ -131,6 +131,7 @@ struct SandboxParameters {
     float specularAntiAliasingVariance = 0.0f;
     float specularAntiAliasingThreshold = 0.0f;
     float transmission = 1.0f;
+    float dispersion = 0.0f;
     float distance = 1.0f;
     float ior = 1.5;
     float emissiveExposureWeight = 1.0f;

samples/materials/sandboxLitSolidRefraction.mat

@@ -56,6 +56,10 @@ material {
             type : float,
             name : transmission
         },
+        {
+            type : float,
+            name : dispersion
+        },
         {
             type : float4,
             name : emissive
@@ -80,6 +84,7 @@ fragment {
         material.thickness = materialParams.thickness;
         material.ior = materialParams.ior;
         material.transmission = materialParams.transmission;
+        material.dispersion = materialParams.dispersion;
         material.emissive = materialParams.emissive;
     }
 }

samples/materials/sandboxLitSolidRefractionSsr.mat

@@ -56,6 +56,10 @@ material {
             type : float,
             name : transmission
         },
+        {
+            type : float,
+            name : dispersion
+        },
         {
             type : float4,
             name : emissive
@@ -80,6 +84,7 @@ fragment {
         material.thickness = materialParams.thickness;
         material.ior = materialParams.ior;
         material.transmission = materialParams.transmission;
+        material.dispersion = materialParams.dispersion;
         material.emissive = materialParams.emissive;
     }
 }