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#version 150 core
layout( triangles ) in;
layout( triangle_strip, max_vertices = 24 ) out;
struct Section {
vec4 equation;
vec3 center;
};
struct SectionsData {
int sectionsCount;
Section sections[8];
};
in VertexData {
vec3 position;
} v_in[];
out FragData {
vec3 fragPosition;
vec3 fragNormal;
} v_out;
uniform SectionsData sectionsData;
uniform mat4 mvp;
const float radius = 1000.0;
void emitQuad(Section section)
{
vec4 equation = section.equation;
vec3 center = section.center;
v_out.fragNormal = equation.xyz;
// generate tangent and bitangent
vec3 u = vec3(1.0f, 1.0f, 1.0f);
// 2 vectors a (xa, ya, za), b (xb, yb, zb) are orthogonal if:
// xaxb + yayb + zazb = 0 <=>
// zb = -(xaxb + yayb) / za
// yb = -(xaxb + zazb) / ya
// xb = -(yayb + zazb) / xa
if (equation.x != 0)
u.x = -(u.y * equation.y + u.z * equation.z) / equation.x;
else if (equation.y != 0)
u.y = -(u.x * equation.x + u.z * equation.z) / equation.y;
else if (equation.z != 0)
u.z = -(u.x* equation.x + u.y * equation.y) / equation.z;
u = normalize(u);
vec3 v = normalize(cross(u, equation.xyz)) * radius;
u *= radius;
v_out.fragPosition = v_in[0].position;
gl_Position = mvp * vec4(center + u + v, 1.0);
EmitVertex();
v_out.fragPosition = v_in[1].position;
gl_Position = mvp * vec4(center + u - v, 1.0);
EmitVertex();
v_out.fragPosition = v_in[2].position;
gl_Position = mvp * vec4(center - u + v, 1.0);
EmitVertex();
v_out.fragPosition = v_in[0].position;
gl_Position = mvp * vec4(center - u - v, 1.0);
EmitVertex();
EndPrimitive();
}
void main()
{
for (int i = 0; i < sectionsData.sectionsCount; ++i) {
emitQuad(sectionsData.sections[i]);
}
}
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