HDRenderPipeline: Update some comment in UI and code

ScriptableRenderPipeline/HDRenderPipeline/Material/LayeredLit/Editor/LayeredLitUI.cs

             public readonly GUIContent vertexColorModeText = new GUIContent("Vertex Color Mode", "Mode multiply: vertex color is multiply with the mask. Mode additive: vertex color values are remapped between -1 and 1 and added to the mask (neutral at 0.5 vertex color).");
             public readonly GUIContent layerCountText = new GUIContent("Layer Count", "Number of layers.");
             public readonly GUIContent layerTilingBlendMaskText = new GUIContent("Tiling", "Tiling for the blend mask.");
-            public readonly GUIContent objectScaleAffectTileText = new GUIContent("Tiling 0123 follow object Scale", "Tiling will be affected by the object scale.");
-            public readonly GUIContent objectScaleAffectTileText2 = new GUIContent("Tiling 123 follow object Scale", "Tiling will be affected by the object scale.");
+            public readonly GUIContent objectScaleAffectTileText = new GUIContent("Lock layers tiling and object Scale", "Tiling of each layers will be affected by the object scale.");
+            public readonly GUIContent objectScaleAffectTileText2 = new GUIContent("Lock influenced layers tiling and object Scale", "Tiling of each influenced layers (all except main layer) will be affected by the object scale.");
 
             public readonly GUIContent layerTexWorldScaleText = new GUIContent("World Scale", "Tiling factor applied to Planar/Trilinear mapping");
             public readonly GUIContent UVBlendMaskText = new GUIContent("BlendMask UV Mapping", "Base UV Mapping mode of the layer.");

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Editor/BaseLitUI.cs

             public static GUIContent horizonFadeText = new GUIContent("Horizon Fade (Spec occlusion)", "horizon fade is use to control specular occlusion");
 
             // Per pixel displacement
-            public static GUIContent enablePerPixelDisplacementText = new GUIContent("Enable Per Pixel Displacement", "");
-            public static GUIContent ppdMinSamplesText = new GUIContent("Minimum samples", "Minimum samples to use with per pixel displacement mapping");
-            public static GUIContent ppdMaxSamplesText = new GUIContent("Maximum samples", "Maximum samples to use with per pixel displacement mapping");
-            public static GUIContent ppdLodThresholdText = new GUIContent("Fading LOD start", "Starting Lod where the parallax occlusion mapping effect start to disappear");
+            public static GUIContent enablePerPixelDisplacementText = new GUIContent("Enable Per Pixel Displacement", "Per pixel displacement work best with flat surfaces. This is an expensive features and should be enable wisely. Typical use case is paved road.");
+            public static GUIContent ppdMinSamplesText = new GUIContent("Minimum steps", "Minimum steps (texture sample) to use with per pixel displacement mapping");
+            public static GUIContent ppdMaxSamplesText = new GUIContent("Maximum steps", "Maximum steps (texture sample) to use with per pixel displacement mapping");
+            public static GUIContent ppdLodThresholdText = new GUIContent("Fading mip level start", "Starting heightmap mipmap lod number where the parallax occlusion mapping effect start to disappear");
 
             // Tessellation
             public static string tessellationModeText = "Tessellation Mode";
             public static GUIContent tessellationFactorTriangleSizeText = new GUIContent("Triangle size", "Desired screen space sized of triangle (in pixel). Smaller value mean smaller triangle.");
             public static GUIContent tessellationShapeFactorText = new GUIContent("Shape factor", "Strength of Phong tessellation shape (lerp factor)");
             public static GUIContent tessellationBackFaceCullEpsilonText = new GUIContent("Triangle culling Epsilon", "If -1.0 back face culling is enabled for tessellation, higher number mean more aggressive culling and better performance");
-            public static GUIContent tessellationObjectScaleText = new GUIContent("Enable object scale", "Tessellation displacement will take into account the object scale - Only work with uniform positive scale");
-            public static GUIContent tessellationTilingScaleText = new GUIContent("Enable tiling scale", "Tessellation displacement will take into account the tiling scale - Only work with uniform positive scale");
+            public static GUIContent tessellationObjectScaleText = new GUIContent("Lock with object scale", "Tessellation displacement will take into account the object scale - Only work with uniform positive scale");
+            public static GUIContent tessellationTilingScaleText = new GUIContent("Lock with heightmap tiling", "Tessellation displacement will take into account the tiling scale - Only work with uniform positive scale");
 
             // Wind
             public static GUIContent windText = new GUIContent("Enable Wind");

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Editor/LitUI.cs

-using System;
+using System;
 using UnityEngine;
 using UnityEngine.Rendering;
 using UnityEngine.Experimental.Rendering;
             public static GUIContent maskMapESText = new GUIContent("Mask Map - M(R), AO(G), E(B), S(A)", "Mask map");
             public static GUIContent maskMapSText = new GUIContent("Mask Map - M(R), AO(G), S(A)", "Mask map");
 
-            public static GUIContent normalMapSpaceText = new GUIContent("Normal/Tangent Map space", "");
+            public static GUIContent normalMapSpaceText = new GUIContent("Normal Map space", "");
             public static GUIContent normalMapText = new GUIContent("Normal Map", "Normal Map (BC7/BC5/DXT5(nm))");
             public static GUIContent normalMapOSText = new GUIContent("Normal Map OS", "Normal Map (BC7/DXT1/RGB)");
             public static GUIContent specularOcclusionMapText = new GUIContent("Specular Occlusion Map (RGBA)", "Specular Occlusion Map");

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/LitData.hlsl

     // The epsilon here also has to be bigger than the epsilon in the next computation.
     float transition = max(_HeightTransition, 1e-5);
 
-    // The goal here is to have all but the heighest layer at negative heights, then we add the transition so that if the next heighest layer is near transition it will have a positive value.
-    // Then we clamp this to zero and normalize everything so that heighest layer has a value of 1.
+    // The goal here is to have all but the highest layer at negative heights, then we add the transition so that if the next highest layer is near transition it will have a positive value.
+    // Then we clamp this to zero and normalize everything so that highest layer has a value of 1.
     maskedHeights = maskedHeights - maxHeight.xxxx;
     // We need to add an epsilon here for active layers (hence the blendMask again) so that at least a layer shows up if everything's too low.
     maskedHeights = (max(0, maskedHeights + transition) + 1e-6) * blendMask.argb;
 
 #if defined(_DENSITY_MODE)
     // Note: blendMasks.argb because a is main layer
-    float4 opacityAsDensity = saturate((inputAlphaMask - (float4(1.0, 1.0, 1.0, 1.0) - blendMasks.argb)) * 20.0);
+    float4 opacityAsDensity = saturate((inputAlphaMask - (float4(1.0, 1.0, 1.0, 1.0) - blendMasks.argb)) * 20.0); // 20.0 is the number of steps in inputAlphaMask (Density mask. We decided 20 empirically)
     float4 useOpacityAsDensityParam = float4(_OpacityAsDensity0, _OpacityAsDensity1, _OpacityAsDensity2, _OpacityAsDensity3);
     blendMasks.argb = lerp(blendMasks.argb, opacityAsDensity, useOpacityAsDensityParam);
 #endif