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#version 400 core
layout( isolines, fractional_even_spacing, ccw ) in;
out Vertex {
vec3 color;
} te_out;
uniform mat4 modelViewMatrix;
uniform mat3 normalMatrix;
uniform mat4 projectionMatrix;
uniform mat4 mvp;
// Calculate RGB triplet from HSV
vec3 hsvToRGB( float h, float s, float v )
{
if ( s <= 0.0 )
return vec3( v );
h = h * 6.0;
float c = v * s;
float x = ( 1.0 - abs( ( mod( h, 2 ) - 1 ) ) ) * c;
float m = v - c;
float r = 0.0;
float g = 0.0;
float b = 0.0;
if ( h < 1.0 ) { r = c; g = x; b = 0.0;}
else if ( h < 2.0 ) { r = x; g = c; b = 0.0; }
else if ( h < 3.0 ) { r = 0.0; g = c; b = x; }
else if ( h < 4.0 ) { r = 0.0; g = x; b = c; }
else if ( h < 5.0 ) { r = x; g = 0.0; b = c; }
else { r = c; g = 0.0; b = x; }
return vec3( r + m, g + m, b + m );
}
void main()
{
float u = gl_TessCoord.x;
float v = gl_TessCoord.y;
vec4 a = gl_in[0].gl_Position;
vec4 b = gl_in[1].gl_Position;
vec4 c = gl_in[2].gl_Position;
vec4 d = gl_in[3].gl_Position;
// Use the (u,v) parametric coords to calculate the vertex.
// u is the position along an isoline
// v is isoline number
// Let's make a sinusoidal curve as a function of u that varies
// in the v direction which we will define as orthogonal to u
// Interpolate in u along top and bottom edges of the patch
vec4 q0 = mix( a, b, u );
vec4 q1 = mix( d, c, u );
// Interpolate in v between the above positions. This gives the
// nominal position for our vertex
vec4 p = mix( q0, q1, v );
// Find "vertical" direction
vec4 vBasis = normalize( q1 - q0 );
// Offset vertex in this direction using sinusoid
vec4 pos = p + 0.2 * vBasis * sin( 20.0 * u );
// Use a hue value based on v
te_out.color = hsvToRGB( v, 1.0, 1.0 );
// Transform to clip-space
gl_Position = mvp * pos;
}
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