From a6b3237211843efffafc3d3999e8c4afd84bcf19 Mon Sep 17 00:00:00 2001
From: Jason <jphillips@ua.edu>
Date: Mon, 12 Sep 2016 11:07:44 -0500
Subject: [PATCH] lens distortion post-processing shader

---
 Data/Sys/Shaders/lens_distortion.glsl | 93 +++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 Data/Sys/Shaders/lens_distortion.glsl

diff --git a/Data/Sys/Shaders/lens_distortion.glsl b/Data/Sys/Shaders/lens_distortion.glsl
new file mode 100644
index 0000000000..35390b4d69
--- /dev/null
+++ b/Data/Sys/Shaders/lens_distortion.glsl
@@ -0,0 +1,93 @@
+/*
+[configuration]
+
+[OptionRangeFloat]
+GUIName = Distortion amount
+OptionName = DISTORTION_FACTOR
+MinValue = 1.0
+MaxValue = 10.0
+StepAmount = 0.5
+DefaultValue = 4.0
+
+[OptionRangeFloat]
+GUIName = Eye Distance Offset
+OptionName = EYE_OFFSET
+MinValue = 0.0
+MaxValue = 10.0
+StepAmount = 0.25
+DefaultValue = 5.0
+
+[OptionRangeFloat]
+GUIName = Zoom adjustment
+OptionName = SIZE_ADJUST
+MinValue = 0.0
+MaxValue = 1.0
+StepAmount = 0.025
+DefaultValue = 0.5
+
+[OptionRangeFloat]
+GUIName = Aspect Ratio adjustment
+OptionName = ASPECT_ADJUST
+MinValue = 0.0
+MaxValue = 1.0
+StepAmount = 0.025
+DefaultValue = 0.5
+
+[/configuration]
+*/
+
+
+void main()
+{
+  // Base Cardboard distortion parameters
+  float factor = GetOption(DISTORTION_FACTOR) * 0.01f;
+  float ka = factor * 3.0f;
+  float kb = factor * 5.0f;
+
+  // size and aspect adjustment
+  float sizeAdjust = 1.0f - GetOption(SIZE_ADJUST) + 0.5f;
+  float aspectAdjustment = 1.25f - GetOption(ASPECT_ADJUST);
+
+  // offset centering per eye
+  float stereoOffset = GetOption(EYE_OFFSET) * 0.01f;
+  float offsetAdd;
+
+  // layer0 = left eye, layer1 = right eye
+  if (layer == 1)
+  {
+    offsetAdd = stereoOffset;
+  }
+  else
+  {
+    offsetAdd = 0 - stereoOffset;
+  }
+
+  // convert coordinates to NDC space
+  float2 fragPos = (GetCoordinates() - 0.5f - vec2(offsetAdd, 0.0f)) * 2.0f;
+
+  // Calculate the source location "radius" (distance from the centre of the viewport)
+  float destR = length(fragPos);
+
+  // find the radius multiplier
+  float srcR = destR * sizeAdjust + ( ka * pow(destR,2) + kb * pow(destR,4));
+
+  // Calculate the source vector (radial)
+  vec2 correctedRadial = normalize(fragPos) * srcR;
+
+  // fix aspect ratio
+  vec2 widenedRadial = correctedRadial * vec2(aspectAdjustment, 1.0f);
+
+  // Transform the coordinates (from [-1,1]^2 to [0, 1]^2)
+  vec2 uv = (widenedRadial/2.0f) + vec2(0.5f) + vec2(offsetAdd, 0.0f);
+
+  // Sample the texture at the source location
+  if (uv[0] > 1.0 || uv[1] > 1.0 || uv[0] < 0.0 || uv[1] < 0.0)
+  {
+    // black if beyond bounds
+    SetOutput(float4(0,0,0,0));
+  }
+  else
+  {
+    SetOutput(SampleLocation(uv));
+  }
+}