3dobs/shaders/grid_v.glsl

#version 330 core
out vec3 nearPoint;
out vec3 farPoint;

uniform mat4 projection;
uniform mat4 view;

// Grid position are in xy clipped space
vec3 gridPlane[6] = vec3[](
    vec3(1, 1, 0), vec3(-1, -1, 0), vec3(-1, 1, 0),
    vec3(-1, -1, 0), vec3(1, 1, 0), vec3(1, -1, 0)
);

vec3 UnprojectPoint(float x, float y, float z, mat4 v, mat4 proj) {
    mat4 viewInv = inverse(v);
    mat4 projInv = inverse(proj);
    vec4 unprojectedPoint =  viewInv * projInv * vec4(x, y, z, 1.0);
    return unprojectedPoint.xyz / unprojectedPoint.w;
}

void main() {
    vec3 p = gridPlane[gl_VertexID].xyz;
    nearPoint = UnprojectPoint(p.x, p.y, 0.0, view, projection).xyz; // unprojecting on the near plane
    farPoint = UnprojectPoint(p.x, p.y, 1.0, view, projection).xyz; // unprojecting on the far plane
    gl_Position = vec4(p, 1.0); // using directly the clipped coordinates
}