From 46026ab9b9704bfd8f31a26bd1ee88873e6e4fe3 Mon Sep 17 00:00:00 2001
From: Evert Prants <imsonotsleepy@gmail.com>
Date: Tue, 31 Mar 2020 15:07:23 +0300
Subject: [PATCH] Sky from atmosphere! Fix normalization

---
 assets/shaders/atmosphere.vs               | 50 ++++++++++++++--------
 src/engine/components/planet/atmosphere.js |  7 +--
 src/engine/utility.js                      |  2 +-
 3 files changed, 38 insertions(+), 21 deletions(-)

diff --git a/assets/shaders/atmosphere.vs b/assets/shaders/atmosphere.vs
index 9276554..a2ced5d 100644
--- a/assets/shaders/atmosphere.vs
+++ b/assets/shaders/atmosphere.vs
@@ -30,35 +30,50 @@ uniform mat4 uModelMatrix;
 uniform mat4 uViewMatrix;
 uniform mat4 uProjectionMatrix;
 
-float scale(float fCos)
-{
+float scale(float fCos) {
 	float x = 1.0 - fCos;
 	return fScaleDepth * exp(-0.00287 + x*(0.459 + x*(3.83 + x*(-6.80 + x*5.25))));
 }
-void main(void)
-{
+
+void main(void) {
 	// Get the ray from the camera to the vertex and its length (which is the far point of the ray passing through the atmosphere)
 	vec3 v3Ray = aVertexPosition - v3CameraPosition;
 	float fFar = length(v3Ray);
 	v3Ray /= fFar;
-	// Calculate the closest intersection of the ray with the outer atmosphere (which is the near point of the ray passing through the atmosphere)
-	float B = 2.0 * dot(v3CameraPosition, v3Ray);
-	float C = fCameraHeight2 - fOuterRadius2;
-	float fDet = max(0.0, B*B - 4.0 * C);
-	float fNear = 0.5 * (-B - sqrt(fDet));
-	// Calculate the ray's starting position, then calculate its scattering offset
-	vec3 v3Start = v3CameraPosition + v3Ray * fNear;
-	fFar -= fNear;
-	float fStartAngle = dot(v3Ray, v3Start) / fOuterRadius;
-	float fStartDepth = exp(-1.0 / fScaleDepth);
-	float fStartOffset = fStartDepth * scale(fStartAngle);
-	//c0 = vec3(1.0, 0, 0) * fStartAngle;
+
+	vec3 v3Start;
+	float fStartAngle;
+	float fStartDepth;
+	float fStartOffset;
+
+	if (fCameraHeight > fOuterRadius) {
+		// Sky from space
+		// Calculate the closest intersection of the ray with the outer atmosphere (which is the near point of the ray passing through the atmosphere)
+		float B = 2.0 * dot(v3CameraPosition, v3Ray);
+		float C = fCameraHeight2 - fOuterRadius2;
+		float fDet = max(0.0, B*B - 4.0 * C);
+		float fNear = 0.5 * (-B - sqrt(fDet));
+
+		// Calculate the ray's starting position, then calculate its scattering offset
+		v3Start = v3CameraPosition + v3Ray * fNear;
+		fFar -= fNear;
+		fStartAngle = dot(v3Ray, v3Start) / fOuterRadius;
+		fStartDepth = exp(-1.0 / fScaleDepth);
+		fStartOffset = fStartDepth * scale(fStartAngle);
+	} else {
+		// Sky from within the atmosphere
+		v3Start = v3CameraPosition;
+		fStartDepth = exp(fScaleOverScaleDepth * (fInnerRadius - fCameraHeight));
+		fStartAngle = dot(v3Ray, v3Start) / length(v3Start);
+		fStartOffset = fStartDepth*scale(fStartAngle);
+	}
+
 	// Initialize the scattering loop variables
 	float fSampleLength = fFar / fSamples;
 	float fScaledLength = fSampleLength * fScale;
 	vec3 v3SampleRay = v3Ray * fSampleLength;
 	vec3 v3SamplePoint = v3Start + v3SampleRay * 0.5;
-	//gl_FrontColor = vec4(0.0, 0.0, 0.0, 0.0);
+
 	// Now loop through the sample rays
 	vec3 v3FrontColor = vec3(0.0, 0.0, 0.0);
 	for(int i=0; i<nSamples; i++)
@@ -72,6 +87,7 @@ void main(void)
 		v3FrontColor += v3Attenuate * (fDepth * fScaledLength);
 		v3SamplePoint += v3SampleRay;
 	}
+
 	// Finally, scale the Mie and Rayleigh colors and set up the varying variables for the pixel shader
 	gl_Position = uProjectionMatrix * uViewMatrix * uModelMatrix * vec4(aVertexPosition,1);
 	c0 = v3FrontColor * (v3InvWavelength * fKrESun);
diff --git a/src/engine/components/planet/atmosphere.js b/src/engine/components/planet/atmosphere.js
index dbf10ea..31b8f1b 100644
--- a/src/engine/components/planet/atmosphere.js
+++ b/src/engine/components/planet/atmosphere.js
@@ -11,7 +11,7 @@ class Atmosphere extends MeshInstance {
     this.wavelength = wavelength
 
     this.Kr = 0.0025
-    this.Km = 0.0010
+    this.Km = 0.0020
     this.ESun = 20.0
     this.g = -0.950
     this.scaleDepth = 0.25
@@ -23,9 +23,10 @@ class Atmosphere extends MeshInstance {
     gl.uniformMatrix4fv(shader.getUniformLocation(gl, 'uModelMatrix'), false, this.transform)
 
     const camHeight = vec3.length(subv3(camera.pos, this.pos))
+    const invWavelength = [1 / Math.pow(this.wavelength[0], 4), 1 / Math.pow(this.wavelength[1], 4), 1 / Math.pow(this.wavelength[2], 4)]
     gl.uniform3fv(shader.getUniformLocation(gl, 'v3CameraPosition'), camera.pos)
-    gl.uniform3fv(shader.getUniformLocation(gl, 'v3LightPosition'), normalv3(sun.pos.slice()))
-    gl.uniform3f(shader.getUniformLocation(gl, 'v3InvWavelength'), 1 / Math.pow(this.wavelength[0], 4), 1 / Math.pow(this.wavelength[1], 4), 1 / Math.pow(this.wavelength[2], 4))
+    gl.uniform3fv(shader.getUniformLocation(gl, 'v3LightPosition'), normalv3(sun.pos))
+    gl.uniform3fv(shader.getUniformLocation(gl, 'v3InvWavelength'), invWavelength)
     gl.uniform1f(shader.getUniformLocation(gl, 'fCameraHeight'), camHeight)
     gl.uniform1f(shader.getUniformLocation(gl, 'fCameraHeight2'), camHeight * camHeight)
     gl.uniform1f(shader.getUniformLocation(gl, 'fInnerRadius'), this.innerRadius)
diff --git a/src/engine/utility.js b/src/engine/utility.js
index 006d8a5..498c8e3 100644
--- a/src/engine/utility.js
+++ b/src/engine/utility.js
@@ -57,7 +57,7 @@ export function divv3 (one, two) {
 }
 
 export function normalv3 (vec) {
-  const res = vec
+  const res = []
   vec3.normalize(res, vec)
   return res
 }