precision highp float;

varying highp vec2 vUv;
varying highp vec2 vL;
varying highp vec2 vR;
varying highp vec2 vT;
varying highp vec2 vB;

uniform sampler2D uPressure;
uniform sampler2D uDivergence;

void main() {
    float L = texture2D(uPressure, vL).x;

    float R = texture2D(uPressure, vR).x;

    float T = texture2D(uPressure, vT).x;

    float B = texture2D(uPressure, vB).x;

    float C = texture2D(uPressure, vUv).x;

    float divergence = texture2D(uDivergence, vUv).x;

    float pressure = (L + R + B + T - divergence) * 0.25;

    gl_FragColor = vec4(pressure, 0.0, 0.0, 1.0);
}