Optimize fog effect.

uniform float2 uvScaleFgd;

uniform float2 uvOffsetBgd;

uniform float2 uvScaleBgd;

uniform half2 timeForeground;

uniform half2 timeBackground;

uniform half timeForeground;

uniform half timeBackground;

uniform half screenAspectRatio;

uniform half2 screenSize;

uniform half pixelDensity;

#include "shaders/constants.agsl"

#include "shaders/utils.agsl"

#include "shaders/simplex_noise.agsl"

#include "shaders/simplex_flow_noise.agsl"

// TODO: explore a more performant way of generating the volumetric fog effect.

const int numOctaves = 2;

float fbm (vec3 st, vec2 time) {

    vec3 p = st;

float fbm(vec2 p, half time) {

    float a = 0.5;

    float result = 0.0;

    float rot = 1.2;

    for (int i = 0; i < numOctaves; i++) {

        result += a * simplex3d(vec3(p.xy + time, p.z));

        result += a * simplex2d_flow(p, rot, time);

        rot *= 1.25;

        p *= 2.0152;

        a *= 0.5;

    }

    vec4 colorForeground = foreground.eval(fragCoord * uvScaleFgd + uvOffsetFgd);

    vec4 color = background.eval(fragCoord * uvScaleBgd + uvOffsetBgd);

    float frontFog = smoothstep(-0.616, 0.552, fbm(vec3(uv * 0.886, 123.1), timeForeground));

    float bgdFog = smoothstep(-0.744, 0.28, fbm(vec3(uv * 1.2, 231.), timeBackground));

    float frontFog = smoothstep(-0.616, 0.552, fbm(uv * 0.8, timeForeground));

    float bgdFog = smoothstep(-0.744, 0.28, fbm(uv * 1.2, timeBackground));

    float dither = 1. - triangleNoise(fragCoord * pixelDensity) * 0.161;

/*

 * Copyright (C) 2023 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

const float SKEW = 0.366025404; // (sqrt(3)-1)/2

const float UNSKEW = 0.211324865; // (3-sqrt(3))/6

half2 hash2d(vec2 p) {

    p = vec2(dot(p,vec2(157.1, 235.7)), dot(p,vec2(573.5, 13.3)));

    return fract(sin(p) * 877.343) * 2. -1.; // [-1, 1]

}

half hash1d(vec2 p) {

    return fract(sin(dot(p, vec2(343.0, 49.0)))) * 2. -1.; // [-1, 1]

}

vec2 getVectorFromAngle(float theta) {

    return vec2(cos(theta), sin(theta));

}

// 2D Simplex noise with dynamic gradient vectors. Return value [-1, 1].

//

// This method produces similar visuals to Simplex noise 3D, but at a lower computational cost.

// The snapshot of the noise is the same as a regular Simplex noise. However, when animated, it

// creates a swirling motion that is more suitable for flow-y effects.

//

// The difference in motion is not noticeable unless the following conditions are met:

// 1) The rotation offset is identical for all vertex gradients.

// 2) The noise is moving quickly.

// 3) The noise is tiled.

//

// This method is recommended for use because it is significantly more performant than 3D Simplex

// noise. It is especially useful for simulating fire, clouds, and fog, which all have advection.

//

// rot is an angle in radian that you want to step for each dt.

float simplex2d_flow(vec2 p, float rot, float time) {

    // Skew the input coordinate and find the simplex index.

    vec2 i = floor(p + (p.x + p.y) * SKEW);

    // First vertex of the triangle.

    vec2 v0 = p - i + (i.x + i.y) * UNSKEW;

    // Find two other vertices.

    // Determines which triangle we should walk.

    // If y>x, m=0 upper triangle, x>y, m=1 lower triangle.

    float side = step(v0.y, v0.x);

    vec2 walk = vec2(side, 1.0 - side);

    vec2 v1 = v0 - walk + UNSKEW;

    vec2 v2 = v0 - 1.0 + 2.*UNSKEW;

    // Get random gradient vector.

    vec2 g0 = hash2d(i);

    vec2 g1 = hash2d(i+walk);

    vec2 g2 = hash2d(i+1.0);

    // Make the gradient vectors dynamic by adding rotations.

    g0 += getVectorFromAngle(rot * time * hash1d(i));

    g1 += getVectorFromAngle(rot * time * hash1d(i+walk));

    g2 += getVectorFromAngle(rot * time * hash1d(i+1.));

    // Kernel summation

    vec3 w = max(0.5 - vec3(dot(v0, v0), dot(v1, v1), dot(v2, v2)), 0.0);

    w = w*w*w*w;

    vec3 n = w * vec3(dot(v0, g0), dot(v1, g1), dot(v2, g2));

    return dot(n, vec3(32.0));

}

) : WeatherEffect {

    private val fogPaint = Paint().also { it.shader = fogConfig.colorGradingShader }

    private val variationFgd: FloatArray = FloatArray(2)

    private val timeFgd: FloatArray = FloatArray(2)

    private val variationBgd: FloatArray = FloatArray(2)

    private val timeBgd: FloatArray = FloatArray(2)

    private var elapsedTime: Float = 0f

    init {

    override fun update(deltaMillis: Long, frameTimeNanos: Long) {

        val time = 0.02f * frameTimeNanos.toFloat() * NANOS_TO_SECONDS

        val variation = sin(time + sin(3f * time)) * 0.5f + 0.5f

        elapsedTime += variation * deltaMillis * MILLIS_TO_SECONDS

        val speed = elapsedTime * 0.248f

        variationFgd[0] = 0.256f * sin(speed)

        variationFgd[1] = 0.156f * sin(speed) * sin(speed)

        timeFgd[0] = 0.04f * elapsedTime * 5f + variationFgd[0]

        timeFgd[1] = 0.003f * elapsedTime * 5f + variationFgd[1]

        // Variation range [1, 1.5]. We don't want the variation to be 0.

        val variation = (sin(time + sin(3f * time)) * 0.5f + 0.5f) * 1.5f

        elapsedTime += variation * deltaMillis * MILLIS_TO_SECONDS

        variationBgd[0] = 0.156f * sin((speed + Math.PI.toFloat() / 2.0f))

        variationBgd[1] = 0.0156f * sin((speed * Math.PI.toFloat() / 3.0f)) * sin(speed)

        timeBgd[0] = 0.08f * elapsedTime * 5f + variationBgd[0]

        timeBgd[1] = 0.02f * elapsedTime * 5f + variationBgd[1]

        fogConfig.shader.setFloatUniform("timeBackground", elapsedTime * 1.5f)

        fogConfig.shader.setFloatUniform("timeForeground", elapsedTime * 2.0f)

        fogConfig.shader.setFloatUniform("timeForeground", timeFgd[0], timeFgd[1])

        fogConfig.shader.setFloatUniform("timeBackground", timeBgd[0], timeBgd[1])

        fogConfig.colorGradingShader.setInputShader("texture", fogConfig.shader)

    }