jit.gl.shader / GLSL でプロシージャルテクスチャ（星）生成 その２ #maxmsp #jitter #glsl

配色がRedbull感

OpenGL Superbibleのサンプルコードです。レッドブルが飲みたくなる配色。

JXS / GLSLコード

<jittershader name="mrr-3colored-lights">
	<description>
	</description>

	<language name="glsl" version="1.2">
		<program name="vp" type="vertex">
<![CDATA[

#version 120 

varying vec3 N,L,V;

void main(void)
{
	vec3 lightPos = gl_LightSource[0].position.xyz;

	gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;	
	
	//map object-space position onto unit sphere
	V =gl_Vertex.xyz;
	
	//eye-space normal
	N = gl_NormalMatrix * gl_Normal;
	
	//eye-space light vector
	vec4 Veye = gl_ModelViewMatrix * gl_Vertex;
	L =lightPos - Veye.xyz;	
}

]]>
		</program>
		<program name="fp" type="fragment">
<![CDATA[

#version 120

varying vec3 V;
varying vec3 N;
varying vec3 L;

const vec3 myRed 	= vec3(0.6,0,0);
const vec3 myYellow = vec3(0.6,0.5,0);
const vec3 myBlue 	= vec3(0,0.3,0.6);

//Star Vertex
const vec3 myHalfSpace0 = vec3(0.31,0.95,0);
const vec3 myHalfSpace1 = vec3(-0.81,0.59,0);
const vec3 myHalfSpace2 = vec3(-0.81,-0.59,0);
const vec3 myHalfSpace3 = vec3(0.31,-0.95,0);
const vec3 myHalfSpace4 = vec3(1.,0.,0.);

const float stripeThickness = 0.4;
const float starSize = 0.2;
const float smoothEdgeTol = 0.005;
const float ambientLighting = 0.5;
const float specularExp = 128.0;
const float specularIntensity = 1.;

void main()
{
	vec4 distVector;
	float distScalar;
	
	vec3 NN = normalize(N);
	vec3 NL = normalize(L); //for ambient;
	vec3 NH = normalize(NL +vec3(0,0,1)); //for specular
	vec3 NV = normalize(V);
	
	float myInOut = -3;
	
	distVector.x = dot(NV, myHalfSpace0);
	distVector.y = dot(NV, myHalfSpace1);
	distVector.z = dot(NV, myHalfSpace2);
	distVector.w = dot(NV, myHalfSpace3);
	distScalar = dot(NV,myHalfSpace4);
	
	distVector += starSize;
	distScalar += starSize;
	
	//map 0 ~ 1
	distVector = smoothstep(0.,smoothEdgeTol, distVector);
	distScalar = smoothstep(0.,smoothEdgeTol, distScalar);
	
	myInOut += dot(distVector, vec4(1.0));
	myInOut += distScalar;
	myInOut = clamp(myInOut, 0,1);
	
	vec3 surfColor = mix(myYellow, myRed, myInOut);
	
	myInOut = smoothstep(0,smoothEdgeTol,abs(NV.z) - stripeThickness);
	surfColor = mix(myBlue,surfColor,myInOut);
	
	surfColor *= (ambientLighting + vec3(max(0,dot(NN,NL))));	
	surfColor += (specularIntensity * vec3(pow(max(0,dot(NN,NH)),specularExp)));
	
	gl_FragColor = vec4(surfColor,1);
}
]]>
		</program>
	</language>
</jittershader>

星の各点との内積をとって、星の頂点方向の長さ（０以上１以下）を合計し星のサイズをオフセットとして加算。その値が閾値を超えたら赤色にして、超えなかったら黄色に塗って星を描画している。星の頂点位置とVertexの単位ベクトルの関係性を使って星の形を描画しているのだが、ちょっとまだ理解しきれていない・・・。

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