Reversed the debug view for displacement to show height instead of depth.

Also add a LerpInverse utility, though I ended up not using it with these changes, it should be handle elsewhere.

Gems/Atom/Feature/Common/Assets/Materials/Types/StandardMultilayerPBR_ForwardPass.azsl

@@ -342,8 +342,11 @@ PbrLightingOutput ForwardPassPS_Common(VSOutput IN, bool isFrontFace, out float
     
     if(o_debugDrawMode == DebugDrawMode::Displacement)
     {
-        float depth = GetNormalizedDepth(-MaterialSrg::m_displacementMax, -MaterialSrg::m_displacementMin, IN.m_uv[MaterialSrg::m_parallaxUvIndex], float2(0,0), float2(0,0));
-        return DebugOutput(float3(depth,depth,depth));
+        float startDepth = -MaterialSrg::m_displacementMax;
+        float stopDepth = -MaterialSrg::m_displacementMin;
+        float depth = GetNormalizedDepth(startDepth, stopDepth, IN.m_uv[MaterialSrg::m_parallaxUvIndex], float2(0,0), float2(0,0));
+        float height = 1 - saturate(depth);
+        return DebugOutput(float3(height,height,height));
     }
     
     if(o_debugDrawMode == DebugDrawMode::FinalBlendWeights)

Gems/Atom/RPI/Assets/ShaderLib/Atom/RPI/Math.azsli

@@ -225,3 +225,16 @@ float NextRandomFloatUniform(inout uint seed)
     seed = Xorshift(seed);
     return (float)seed /  4294967295.0f;
 }
+
+//! Returns the inverse of lerp, 't', such that value = lerp(a, b, t), or returns 0 when a == b.
+float LerpInverse(float a, float b, float value)
+{
+    if(abs(a - b) <= EPSILON)
+    {
+        return 0.0;
+    }
+    else
+    {
+        return (value - a) / (b - a);
+    }
+}