processing4/java/examples/Topics/Shaders/DomeProjection/data/cubemapvert.glsl

uniform mat4 transform;
uniform mat4 modelview;
uniform mat3 normalMatrix;

attribute vec4 vertex;
attribute vec3 normal;

varying vec3 reflectDir;

void main() {
  gl_Position = transform * vertex;
    
  vec3 ecNormal = normalize(normalMatrix * normal); // Vertex in eye coordinates
  vec3 ecVertex = vec3(modelview * vertex); // Normal vector in eye coordinates
  vec3 eyeDir = ecVertex.xyz;
  reflectDir = reflect(eyeDir, ecNormal);
}