Review VR simulator mechanism

- No default VR device parameteres inside raylib
- VR device parameter should be provided by user
- VR distortion shader should be provided by user

examples/core/core_vr_simulator.c

@@ -23,7 +23,35 @@ int main()
     InitWindow(screenWidth, screenHeight, "raylib [core] example - vr simulator");
 
     // Init VR simulator (Oculus Rift CV1 parameters)
-    InitVrSimulator(GetVrDeviceInfo(HMD_OCULUS_RIFT_CV1));
+    InitVrSimulator();
+
+    VrDeviceInfo hmd = { 0 };               // VR device parameters (head-mounted-device)
+    
+    // Oculus Rift CV1 parameters for simulator
+    hmd.hResolution = 2160;                 // HMD horizontal resolution in pixels
+    hmd.vResolution = 1200;                 // HMD vertical resolution in pixels
+    hmd.hScreenSize = 0.133793f;            // HMD horizontal size in meters
+    hmd.vScreenSize = 0.0669f;              // HMD vertical size in meters
+    hmd.vScreenCenter = 0.04678f;           // HMD screen center in meters
+    hmd.eyeToScreenDistance = 0.041f;       // HMD distance between eye and display in meters
+    hmd.lensSeparationDistance = 0.07f;     // HMD lens separation distance in meters
+    hmd.interpupillaryDistance = 0.07f;     // HMD IPD (distance between pupils) in meters
+    
+    // NOTE: CV1 uses a Fresnel-hybrid-asymmetric lenses with specific distortion compute shaders.
+    // Following parameters are an approximation to distortion stereo rendering but results differ from actual device.
+    hmd.lensDistortionValues[0] = 1.0f;     // HMD lens distortion constant parameter 0
+    hmd.lensDistortionValues[1] = 0.22f;    // HMD lens distortion constant parameter 1
+    hmd.lensDistortionValues[2] = 0.24f;    // HMD lens distortion constant parameter 2
+    hmd.lensDistortionValues[3] = 0.0f;     // HMD lens distortion constant parameter 3
+    hmd.chromaAbCorrection[0] = 0.996f;     // HMD chromatic aberration correction parameter 0
+    hmd.chromaAbCorrection[1] = -0.004f;    // HMD chromatic aberration correction parameter 1
+    hmd.chromaAbCorrection[2] = 1.014f;     // HMD chromatic aberration correction parameter 2
+    hmd.chromaAbCorrection[3] = 0.0f;       // HMD chromatic aberration correction parameter 3
+    
+    // Distortion shader (uses device lens distortion and chroma)
+    Shader distortion = LoadShader(0, "resources/distortion.fs");
+    
+    SetVrConfiguration(hmd, distortion);    // Set Vr device parameters for stereo rendering
     
     // Define the camera to look into our 3d world
     Camera camera;
@@ -77,9 +105,11 @@ int main()
 
     // De-Initialization
     //--------------------------------------------------------------------------------------
-    CloseVrSimulator();     // Close VR simulator
-    
-    CloseWindow();          // Close window and OpenGL context
+    UnloadShader(distortion);   // Unload distortion shader
+
+    CloseVrSimulator();         // Close VR simulator
+
+    CloseWindow();              // Close window and OpenGL context
     //--------------------------------------------------------------------------------------
 
     return 0;

examples/core/resources/distortion.fs

@@ -0,0 +1,43 @@
+#version 330
+
+in vec2 fragTexCoord;
+in vec4 fragColor;
+out vec4 finalColor;
+
+uniform sampler2D texture0;
+uniform vec2 leftLensCenter = vec2(0.288, 0.5);
+uniform vec2 rightLensCenter = vec2(0.712, 0.5);
+uniform vec2 leftScreenCenter = vec2(0.25, 0.5);
+uniform vec2 rightScreenCenter = vec2(0.75, 0.5);
+uniform vec2 scale = vec2(0.25, 0.45);
+uniform vec2 scaleIn = vec2(4, 2.2222);
+uniform vec4 hmdWarpParam = vec4(1, 0.22, 0.24, 0);
+uniform vec4 chromaAbParam = vec4(0.996, -0.004, 1.014, 0.0);
+
+void main()
+{
+    vec2 lensCenter = fragTexCoord.x < 0.5? leftLensCenter : rightLensCenter;
+    vec2 screenCenter = fragTexCoord.x < 0.5? leftScreenCenter : rightScreenCenter;
+    vec2 theta = (fragTexCoord - lensCenter)*scaleIn;
+    float rSq = theta.x*theta.x + theta.y*theta.y;
+    vec2 theta1 = theta*(hmdWarpParam.x + hmdWarpParam.y*rSq + hmdWarpParam.z*rSq*rSq + hmdWarpParam.w*rSq*rSq*rSq);
+    vec2 thetaBlue = theta1*(chromaAbParam.z + chromaAbParam.w*rSq);
+    vec2 tcBlue = lensCenter + scale*thetaBlue;
+
+    if (any(bvec2(clamp(tcBlue, screenCenter - vec2(0.25, 0.5), screenCenter + vec2(0.25, 0.5)) - tcBlue)))
+    {
+        finalColor = vec4(0.0, 0.0, 0.0, 1.0);
+    }
+    else
+    {
+        float blue = texture(texture0, tcBlue).b;
+        vec2 tcGreen = lensCenter + scale*theta1;
+        float green = texture(texture0, tcGreen).g;
+
+        vec2 thetaRed = theta1*(chromaAbParam.x + chromaAbParam.y*rSq);
+        vec2 tcRed = lensCenter + scale*thetaRed;
+
+        float red = texture(texture0, tcRed).r;
+        finalColor = vec4(red, green, blue, 1.0);
+    }
+};