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Given the Point A with the coordinates gl_FragCoord.xy, I have to find the distance to the Center of the cube face to which it belongs in screen coordinates.

Specifically what I need is the formula to convert the Center of every face of the cube in screen coordinates, in order to compare it with gl_FragCoord.

This the fragment shader:

precision mediump float;

uniform vec2 u_resolution;

varying vec2 v_uv;

void main() {
  gl_FragColor = vec4(v_uv.x, v_uv.y, 0.0, 1.0);
}

This the vertex shader:

precision mediump float;

attribute vec3 a_position;
attribute vec2 a_uv;

uniform mat4 u_view;
uniform mat4 u_projection;

varying vec2 v_uv;

void main() {
  v_uv = a_uv;

  gl_Position = u_projection * u_view * vec4(a_position, 1.0);
}

enter image description here

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  • $\begingroup$ You can't calculate the center of the face in the shader, instead you have to supply it to the shader as attribute vec3 a_face_center; The good news is that you can calculate the distance to the center in the vertex shader, which will then be interpolated per-fragment. $\endgroup$ – zoran404 Apr 10 '20 at 17:34

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