Fix bad state after setIndirectLight(null).

This cleans up 3 related issues, but only the first of these caused an
actual user-visible bug:

(1) When the IBL was null, prepareLighting was failing to bind the black
1x1 texture.

(2) If you added and removed an IBL from a Scene, then Scene was not
returned to its initial state.

(3) The default 1x1 IBL used an intensity of 1 rather than 30000, which
is inconsistent with the null IBL.

Fixes #1940.

RELEASE_NOTES.md

@@ -8,6 +8,8 @@ A new header is inserted each time a *tag* is created.
 
 - Improve high roughness material rendering by default when regenerating environments maps
 
+- Fix bad state after removing an IBL from the Scene.
+
 ## v1.4.3
 
 - Fixed an assertion when a parameter array occurs last in a material definition.

filament/src/Engine.cpp

@@ -236,7 +236,6 @@ void FEngine::init() {
     mDefaultIbl = upcast(IndirectLight::Builder()
             .reflections(mDefaultIblTexture)
             .irradiance(3, reinterpret_cast<const float3*>(sh))
-            .intensity(1.0f)
             .build(*this));
 
     // Always initialize the default material, most materials' depth shaders fallback on it.

filament/src/IndirectLight.cpp

@@ -45,7 +45,7 @@ struct IndirectLight::BuilderDetails {
     Texture const* mIrradianceMap = nullptr;
     float3 mIrradianceCoefs[9] = {};
     mat3f mRotation = {};
-    float mIntensity = 30000.0f;
+    float mIntensity = FIndirectLight::DEFAULT_INTENSITY;
 };
 
 using BuilderType = IndirectLight;

filament/src/Scene.cpp

@@ -42,8 +42,7 @@ namespace details {
 // ------------------------------------------------------------------------------------------------
 
 FScene::FScene(FEngine& engine) :
-        mEngine(engine),
-        mIndirectLight(engine.getDefaultIndirectLight()) {
+        mEngine(engine) {
 }
 
 FScene::~FScene() noexcept = default;

filament/src/View.cpp

@@ -337,24 +337,29 @@ void FView::prepareLighting(FEngine& engine, FEngine::DriverApi& driver, ArenaSc
     u.setUniform(offsetof(PerViewUib, exposure), exposure);
     u.setUniform(offsetof(PerViewUib, ev100), ev100);
 
-    // IBL
-    FIndirectLight const* const ibl = scene->getIndirectLight();
+    // If the scene does not have an IBL, use the black 1x1 IBL and honor the fallback intensity
+    // associated with the skybox.
+    FIndirectLight const* ibl = scene->getIndirectLight();
+    float intensity;
     if (UTILS_LIKELY(ibl)) {
-        float2 iblMaxMipLevel{ ibl->getMaxMipLevel(), 1u << ibl->getMaxMipLevel() };
-        u.setUniform(offsetof(PerViewUib, iblMaxMipLevel), iblMaxMipLevel);
-        u.setUniform(offsetof(PerViewUib, iblLuminance), ibl->getIntensity() * exposure);
-        u.setUniformArray(offsetof(PerViewUib, iblSH), ibl->getSH(), 9);
-        if (ibl->getReflectionMap()) {
-            mPerViewSb.setSampler(PerViewSib::IBL_SPECULAR, {
-                    ibl->getReflectionMap(), {
-                            .filterMag = SamplerMagFilter::LINEAR,
-                            .filterMin = SamplerMinFilter::LINEAR_MIPMAP_LINEAR
-                    }});
-        }
+        intensity = ibl->getIntensity();
     } else {
+        ibl = engine.getDefaultIndirectLight();
         FSkybox const* const skybox = scene->getSkybox();
-        const float intensity = skybox ? skybox->getIntensity() : FIndirectLight::DEFAULT_INTENSITY;
-        u.setUniform(offsetof(PerViewUib, iblLuminance), intensity * exposure);
+        intensity = skybox ? skybox->getIntensity() : FIndirectLight::DEFAULT_INTENSITY;
+    }
+
+    // Set up uniforms and sampler for the IBL, guaranteed to be non-null at this point.
+    float2 iblMaxMipLevel{ ibl->getMaxMipLevel(), 1u << ibl->getMaxMipLevel() };
+    u.setUniform(offsetof(PerViewUib, iblMaxMipLevel), iblMaxMipLevel);
+    u.setUniform(offsetof(PerViewUib, iblLuminance), intensity * exposure);
+    u.setUniformArray(offsetof(PerViewUib, iblSH), ibl->getSH(), 9);
+    if (ibl->getReflectionMap()) {
+        mPerViewSb.setSampler(PerViewSib::IBL_SPECULAR, {
+                ibl->getReflectionMap(), {
+                        .filterMag = SamplerMagFilter::LINEAR,
+                        .filterMin = SamplerMinFilter::LINEAR_MIPMAP_LINEAR
+                }});
     }
 
     // Directional light (always at index 0)

filament/src/details/IndirectLight.h

@@ -35,7 +35,7 @@ class FEngine;
 
 class FIndirectLight : public IndirectLight {
 public:
-    static constexpr float DEFAULT_INTENSITY = 30000.0f;    // lux
+    static constexpr float DEFAULT_INTENSITY = 30000.0f;    // lux of the sun
 
     FIndirectLight(FEngine& engine, const Builder& builder) noexcept;