Idea of using instancing with pixel discard in WebGL

shaders.glsl

// vertex shader
attribute float a_eyeOffset;
varying float v_eyeOffset;

...

vec4 mvPosition = modelViewPosition * vec4(position, 1.0);
mvPosition.x -= a_eyeOffset;
gl_Position = projectionMatrix * mvPosition;
gl_Position.x = gl_Position.x * 0.5 + sign(a_eyeOffset) * 0.5 * gl_Position.w;

v_eyeOffset = a_eyeOffset;


// fragment shader
uniform vec2 u_screenResolution;
varying float v_eyeOffset;

...

void main() {
    
    if((step(0.5, gl_FragCoord.x / u_screenResolution.x) - 0.5) * v_eyeOffset < 0.0) discard;