More improvements to SSAO

- we add an 'intensity' parameter that allows to control the strength
  of the AO effect. This is useful for aesthetic reasons.

- the default intensity is now 2x that of before this change, which
  makes the intensity parameter match AO papers this implementation
  is inspired of.

- bias is now z-dependent, which reduces some self shadowing wrt the
  depth.

android/filament-android/src/main/cpp/View.cpp

@@ -241,8 +241,14 @@ Java_com_google_android_filament_View_nGetAmbientOcclusion(JNIEnv*, jclass, jlon
 
 extern "C" JNIEXPORT void JNICALL
 Java_com_google_android_filament_View_nSetAmbientOcclusionOptions(JNIEnv*, jclass,
-    jlong nativeView, jfloat radius, jfloat bias, jfloat power, jfloat resolution) {
+    jlong nativeView, jfloat radius, jfloat bias, jfloat power, jfloat resolution, jfloat intensity) {
     View* view = (View*) nativeView;
-    View::AmbientOcclusionOptions options = { .radius = radius, .bias = bias, .power = power, .resolution = resolution};
+    View::AmbientOcclusionOptions options = {
+            .radius = radius,
+            .bias = bias,
+            .power = power,
+            .resolution = resolution,
+            .intensity = intensity
+    };
     view->setAmbientOcclusionOptions(options);
 }

android/filament-android/src/main/java/com/google/android/filament/View.java

@@ -149,6 +149,11 @@ public class View {
          * How each dimension of the AO buffer is scaled. Must be positive and <= 1.
          */
         public float resolution = 0.5f;
+
+        /**
+         * Strength of the Ambient Occlusion effect. Must be positive.
+         */
+        public float intensity = 1.0f;
     }
 
     /**
@@ -761,7 +766,8 @@ public class View {
      */
     public void setAmbientOcclusionOptions(@NonNull AmbientOcclusionOptions options) {
         mAmbientOcclusionOptions = options;
-        nSetAmbientOcclusionOptions(getNativeObject(), options.radius, options.bias, options.power, options.resolution);
+        nSetAmbientOcclusionOptions(getNativeObject(), options.radius, options.bias, options.power,
+                options.resolution, options.intensity);
     }
 
     /**
@@ -819,5 +825,5 @@ public class View {
     private static native boolean nIsFrontFaceWindingInverted(long nativeView);
     private static native void nSetAmbientOcclusion(long nativeView, int ordinal);
     private static native int nGetAmbientOcclusion(long nativeView);
-    private static native void nSetAmbientOcclusionOptions(long nativeView, float radius, float bias, float power, float resolution);
+    private static native void nSetAmbientOcclusionOptions(long nativeView, float radius, float bias, float power, float resolution, float intensity);
 }

filament/include/filament/View.h

@@ -147,9 +147,10 @@ public:
      */
     struct AmbientOcclusionOptions {
         float radius = 0.3f;    //!< Ambient Occlusion radius in meters, between 0 and ~10.
-        float bias = 0.005f;    //!< Self-occlusion bias in meters. Use to avoid self-occlusion. Between 0 and a few mm.
+        float bias = 0.0001f;   //!< Self-occlusion bias in meters. Use to avoid self-occlusion. Between 0 and a few mm.
         float power = 0.0f;     //!< Controls ambient occlusion's contrast. Between 0 (linear) and 1 (squared)
         float resolution = 0.5; //!< How each dimension of the AO buffer is scaled. Must be positive and <= 1.
+        float intensity = 1.0;  //!< Strength of the Ambient Occlusion effect.
     };
 
     /**

filament/src/PostProcessManager.cpp

@@ -377,6 +377,7 @@ FrameGraphId<FrameGraphTexture> PostProcessManager::ssao(FrameGraph& fg, RenderP
                 pInstance->setParameter("projectionScaleRadius", projectionScale * data.options.radius);
                 pInstance->setParameter("bias", data.options.bias);
                 pInstance->setParameter("power", data.options.power);
+                pInstance->setParameter("intensity", std::max(0.0f, data.options.intensity));
                 pInstance->setParameter("maxLevel", uint32_t(levelCount - 1));
                 pInstance->commit(driver);
 

filament/src/materials/sao.mat

@@ -30,6 +30,10 @@ material {
             type : float,
             name : power
         },
+        {
+            type : float,
+            name : intensity
+        },
         {
             type : int,
             name : maxLevel
@@ -234,7 +238,7 @@ fragment {
         float vn = dot(v, normal);  // distance * cos(v, normal)
         const float uu = 0.015;
         float falloff = saturate(1.0 - vv * materialParams.invRadiusSquared);
-        float occlusion = falloff * max(0.0, vn - materialParams.bias) / (vv + uu);
+        float occlusion = falloff * max(0.0, vn + origin.z * materialParams.bias) / (vv + uu);
         return occlusion;
     }
 
@@ -258,7 +262,7 @@ fragment {
             occlusion += computeAmbientOcclusionSAO(i, ssDiskRadius, ssOrigin, origin, normal, noise);
         }
 
-        float ao = 1.0 - occlusion / float(kSpiralSampleCount);
+        float ao = max(0.0, 1.0 - (2.0 / float(kSpiralSampleCount)) * materialParams.intensity * occlusion);
 
         // simulate user-controled ao^n with n[1, 2]
         ao = mix(ao, ao * ao, materialParams.power);

samples/material_sandbox.cpp

@@ -347,7 +347,8 @@ static void gui(filament::Engine* engine, filament::View*) {
                 DebugRegistry& debug = engine->getDebugRegistry();
                 ImGui::Checkbox("enabled###ssao", &params.ssao);
                 ImGui::SliderFloat("radius", &params.ssaoOptions.radius, 0.05f, 5.0f);
-                ImGui::SliderFloat("bias", &params.ssaoOptions.bias, 0.0f, 0.1f);
+                ImGui::SliderFloat("bias", &params.ssaoOptions.bias, 0.0f, 0.01f, "%.6f");
+                ImGui::SliderFloat("intensity", &params.ssaoOptions.intensity, 0.0f, 10.0f);
                 ImGui::SliderFloat("power", &params.ssaoOptions.power, 0.0f, 1.0f);
             }
             ImGui::Unindent();