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.buildinfo

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+# Sphinx build info version 1
+# This file hashes the configuration used when building these files. When it is not found, a full rebuild will be done.
+config: 1175a46036eec01bc34a11c2c5ef8932
+tags: 645f666f9bcd5a90fca523b33c5a78b7

_sources/index.rst.txt

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+
+Homepage
+========
+
+.. toctree::
+   :caption: Content Creation Guide
+   :glob:
+   :titlesonly:
+
+   source/social/project
+   source/social/*
+
+.. toctree::
+   :caption: Graphics Programming Blog
+   :glob:
+   :titlesonly:
+
+   source/blog/cpp
+   source/blog/*

_sources/source/blog/autoexposure.rst.txt

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+
+Temporal Auto-Exposure with Hardware Blending
+=============================================
+
+Some graphics pipelines compute auto-exposure like this:
+   :Textures:
+      #. Previous average brightness
+      #. Current average brightness
+   :Passes:
+      #. Store previously generated average brightness
+      #. Generates current average brightness
+      #. Smooth average brightnesses and compute auto-exposure
+
+You can use hardware blending for auto-exposure:
+   :Textures:
+      #. Average brightnesses (previous + current)
+   :Passes:
+      #. Generate and smooth average brightnesses
+      #. Compute auto-exposure
+
+Source Code
+-----------
+
+::
+
+   /*
+      Automatic exposure shader using hardware blending
+   */
+
+   /*
+      Vertex shaders
+   */
+
+   struct APP2VS
+   {
+      float4 HPos : POSITION;
+      float2 Tex0 : TEXCOORD0;
+   };
+
+   struct VS2PS
+   {
+      float4 HPos : POSITION;
+      float2 Tex0 : TEXCOORD0;
+   };
+
+   VS2PS VS_Quad(APP2VS Input)
+   {
+      VS2PS Output;
+      Output.HPos = Input.HPos;
+      Output.Tex0 = Input.Tex0;
+      return Output;
+   }
+
+   /*
+      Pixel shaders
+      ---
+      AutoExposure(): https://knarkowicz.wordpress.com/2016/01/09/automatic-exposure/
+   */
+
+   float3 GetAutoExposure(float3 Color, float2 Tex)
+   {
+      float LumaAverage = exp(tex2Dlod(SampleLumaTex, float4(Tex, 0.0, 99.0)).r);
+      float Ev100 = log2(LumaAverage * 100.0 / 12.5);
+      Ev100 -= _ManualBias; // optional manual bias
+      float Exposure = 1.0 / (1.2 * exp2(Ev100));
+      return Color * Exposure;
+   }
+
+   float4 PS_GenerateAverageLuma(VS2PS Input) : COLOR0
+   {
+      float4 Color = tex2D(SampleColorTex, Input.Tex0);
+      float3 Luma = max(Color.r, max(Color.g, Color.b));
+
+      // OutputColor0.rgb = Output the highest brightness out of red/green/blue component
+      // OutputColor0.a = Output the weight for temporal blending
+      float Delay = 1e-3 * _Frametime;
+      return float4(log(max(Luma.rgb, 1e-2)), saturate(Delay * _SmoothingSpeed));
+   }
+
+   float3 PS_Exposure(VS2PS Input) : COLOR0
+   {
+      float4 Color = tex2D(SampleColorTex, Input.Tex0);
+      return GetAutoExposure(Color.rgb, Input.Tex0);
+   }
+
+   technique AutoExposure
+   {
+      // Pass0: This shader renders to a texture that blends itself
+      // NOTE: Do not have another shader overwrite the texture
+      pass GenerateAverageLuma
+      {
+         // Use hardware blending
+         BlendEnable = TRUE;
+         BlendOp = ADD;
+         SrcBlend = SRCALPHA;
+         DestBlend = INVSRCALPHA;
+
+         VertexShader = VS_Quad;
+         PixelShader = PS_GenerateAverageLuma;
+      }
+
+      // Pass1: Get the texture generated from Pass0
+      // Do autoexposure shading here
+      pass ApplyAutoExposure
+      {
+         VertexShader = VS_Quad;
+         PixelShader = PS_Exposure;
+      }
+   }

_sources/source/blog/censustransform.rst.txt

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+
+Census Transform in HLSL
+========================
+
+The census transform is a filter that represents the pixel's neighborhood relationship in a binary string. The binary string will be ``0000000`` if the center pixel is lesser than all of its neighbors. The binary string will be ``11111111`` if the center pixel is greater than or equal to all of its neighbors.
+
+The filter does not depend on the image's actual intensity. As a result, the filter is robust to illumination.
+
+Source Code
+-----------
+
+::
+
+   float GetGreyScale(float3 Color)
+   {
+      return max(max(Color.r, Color.g), Color.b);
+   }
+
+   float GetCensusTransform(sampler SampleImage, float2 Tex, float2 PixelSize)
+   {
+      float OutputColor = 0.0;
+      float4 ColumnTex[3];
+      ColumnTex[0] = Tex.xyyy + (float4(-1.0, +1.0, 0.0, -1.0) * PixelSize.xyyy);
+      ColumnTex[1] = Tex.xyyy + (float4( 0.0, +1.0, 0.0, -1.0) * PixelSize.xyyy);
+      ColumnTex[2] = Tex.xyyy + (float4(+1.0, +1.0, 0.0, -1.0) * PixelSize.xyyy);
+      
+      const int Neighbors = 8;
+      float SampleNeighbor[Neighbors];
+      SampleNeighbor[0] = GetGreyScale(tex2D(SampleImage, ColumnTex[0].xy).rgb);
+      SampleNeighbor[1] = GetGreyScale(tex2D(SampleImage, ColumnTex[1].xy).rgb);
+      SampleNeighbor[2] = GetGreyScale(tex2D(SampleImage, ColumnTex[2].xy).rgb);
+      SampleNeighbor[3] = GetGreyScale(tex2D(SampleImage, ColumnTex[0].xz).rgb);
+      SampleNeighbor[4] = GetGreyScale(tex2D(SampleImage, ColumnTex[2].xz).rgb);
+      SampleNeighbor[5] = GetGreyScale(tex2D(SampleImage, ColumnTex[0].xw).rgb);
+      SampleNeighbor[6] = GetGreyScale(tex2D(SampleImage, ColumnTex[1].xw).rgb);
+      SampleNeighbor[7] = GetGreyScale(tex2D(SampleImage, ColumnTex[2].xw).rgb);
+      float CenterSample = GetGreyScale(tex2D(SampleImage, ColumnTex[1].xz).rgb);
+
+      // Generate 8-bit integer from the 8-pixel neighborhood
+      for(int i = 0; i < Neighbors; i++)
+      {
+         float Comparison = step(SampleNeighbor[i], CenterSample);
+         OutputColor += ldexp(Comparison, i);
+      }
+
+      // Convert the 8-bit integer to float, and average the results from each channel
+      return OutputColor * (1.0 / (exp2(8) - 1));
+   }

_sources/source/blog/chromaticity.rst.txt

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+
+Chromaticity in HLSL
+====================
+
+Images often represent color in 3 channels: ``(R, G, B)`` - red, green, and blue. You can represent ``(R, G, B)`` in any range. For this post, the range is a minimum of **0.0** and a maximum of **1.0**.
+
+Normalized Chromaticity
+-----------------------
+
+Formulas
+^^^^^^^^
+
+Normalized RG/RGB
+   .. math::
+
+      r = \frac{R}{R+G+B}\\
+      g = \frac{G}{R+G+B}\\
+      b = \frac{B}{R+G+B}\\
+      \\
+      r+g+b = 1
+
+   Output :math:`(r,g,b)`
+      :(1.0, 0.0, 0.0): 100% red
+      :(0.0, 1.0, 0.0): 100% green
+      :(0.0, 0.0, 1.0): 100% blue
+
+   Output :math:`(r,g)`
+      :\(1.0, 0.0\): 100% red
+      :\(0.0, 1.0\): 100% green
+      :\(0.0, 0.0\): 100% blue
+
+Normalized RG/RGB White-Point
+   .. math:: 
+
+      R=1\\
+      G=1\\
+      B=1\\
+      \\
+      r = \frac{R}{R+G+B}\\
+      g = \frac{G}{R+G+B}\\
+      b = \frac{B}{R+G+B}\\
+      \\
+      r+g+b = 1
+
+Source Code
+^^^^^^^^^^^
+
+::
+
+   float3 GetRGBChromaticity(float3 Color)
+   {
+      // Optimizes 2 ADD instructions 1 DP3 instruction
+      float SumRGB = dot(Color, 1.0);
+      float3 Chromaticity = saturate(Color / SumRGB);
+      // Output the chromaticity's white point if the divisor is 0.0
+      // Prevents undefined behavior happens when you divide by 0
+      Chromaticity = (SumRGB == 0.0) ? 1.0 / 3.0 : Chromaticity;
+      return Chromaticity;
+   }
+
+Spherical Chromaticity
+----------------------
+
+This post introduces a color space that computes chromaticity with angles.
+
+Precision Loss in RG Chromaticity
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Pecision is a major drawback to RG chromaticity. In RG chromaticity, all possible values map into a right-triangle, eliminating half of the precision in integer buffers.
+
+We can encode data that fits in the entire ``RG8`` range by calculating the angles between the channels.
+
+Source Code
+^^^^^^^^^^^
+
+::
+
+    /*
+        This code is based on the algorithm described in the following paper:
+        Author(s): Joost van de Weijer, T. Gevers
+        Title: "Robust optical flow from photometric invariants"
+        Year: 2004
+        DOI: 10.1109/ICIP.2004.1421433
+        Link: https://www.researchgate.net/publication/4138051_Robust_optical_flow_from_photometric_invariants
+    */
+
+    float2 GetSphericalRG(float3 Color)
+    {
+        const float HalfPi = 1.0 / acos(0.0);
+
+        // Precalculate (x*x + y*y)^0.5 and (x*x + y*y + z*z)^0.5
+        float L1 = length(Color.rg);
+        float L2 = length(Color.rgb);
+
+        float2 Angles = 0.0;
+        Angles[0] = (L1 == 0.0) ? 1.0 / sqrt(2.0) : Color.g / L1;
+        Angles[1] = (L2 == 0.0) ? 1.0 / sqrt(3.0) : L1 / L2;
+
+        return saturate(asin(abs(Angles)) * HalfPi);
+    }

_sources/source/blog/coordinatespaces.rst.txt

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+
+Coordinate Spaces: A Refresher
+==============================
+
+Standard Basis
+    Defines the directions of the x-axis, y-axis, and z-axis.
+
+    :(1.0, 0.0, 0.0): x-axis
+    :(0.0, 1.0, 0.0): y-axis
+    :(0.0, 0.0, 1.0): z-axis
+
+
+.. list-table:: Coordinate Spaces
+    :header-rows: 1
+
+    * - Coordinate Space
+      - Standard-Basis Location
+      - (0.0, 0.0, 0.0) Location
+    * - Tangent-Space
+      - On the **face or vertex**.
+      - On the center of the **face or vertex**.
+    * - Object-Space
+      - On the **object**.
+      - On the center of the **object**.
+    * - World-Space
+      - On the **world**.
+      - On the center of the **world**.
+    * - View-Space
+      - On the **viewer**.
+      - On the center of the **viewer**.
+