1/*
2 * Copyright (C) 2024 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17uniform shader foreground;
18uniform shader background;
19uniform shader outlineBuffer;
20uniform float2 uvOffsetFgd;
21uniform float2 uvScaleFgd;
22uniform float2 uvOffsetBgd;
23uniform float2 uvScaleBgd;
24uniform float time;
25uniform float screenAspectRatio;
26uniform float2 screenSize;
27uniform half intensity;
28
29#include "shaders/constants.agsl"
30#include "shaders/utils.agsl"
31#include "shaders/rain_shower.agsl"
32#include "shaders/rain_constants.agsl"
33#include "shaders/rain_splash.agsl"
34
35// Controls how visible the rain drops are.
36const float rainVisibility = 0.4;
37
38/**
39 * Draws splashes around the outline of the given image.
40 */
41vec3 drawSplashes(vec2 uv, vec2 fragCoord, vec3 color) {
42    /** 1. Make a grid */
43    vec2 gridSize = vec2(15., 15.);
44    // Aspect ratio impacts visible cells.
45    gridSize.y /= screenAspectRatio;
46    // Scale the UV to allocate number of rows and columns.
47    vec2 gridUv = uv * gridSize;
48    // Invert y (otherwise it goes from 0=top to 1=bottom).
49    gridUv.y = 1. - gridUv.y;
50    // Generate column id, to offset columns vertically (so rain is not aligned).
51    float columnOffset = idGenerator(floor(gridUv.x));
52    gridUv.y += columnOffset * 2.6;
53
54    // For each cell, we set the internal UV from -0.5 (left, bottom) to 0.5 (right, top).
55    vec2 cellUv = fract(gridUv) - 0.5;
56    vec2 pixUv = cellUv;
57    pixUv.x *= -1;
58    vec2 pixDistance = screenSize * pixUv / gridSize;
59    float2 uvTextureFgd = (fragCoord + pixDistance) * uvScaleFgd + uvOffsetFgd;
60
61    float outline = step(0.1, outlineBuffer.eval(uvTextureFgd).r);
62    if (outline < 0.1) {
63        // Simply return the given color when it's not considered as an outline.
64        return color;
65    }
66
67    float t = time + 53.512 * columnOffset;
68    float delay = 1.5173;
69    float duration = 1.2;
70
71    float circletime = floor(t / (duration + delay));
72    // Get the cell ID based on the grid position. [0, 1].
73    float cellId = idGenerator(floor(gridUv) + vec2(circletime, 23.14));
74    // Normalized time [0, 1].
75    float cellTime = max((mod(t + delay * cellId, duration + delay) - delay) / duration, 0.);
76
77    float splash = drawSplash(cellUv, cellTime) * smoothstep(0., 0.45, intensity);
78
79    return normalBlendWithWhiteSrc(color, splash);
80}
81
82vec4 main(float2 fragCoord) {
83    float2 uv = fragCoord / screenSize;
84
85    // Adjusts the UVs to have the expected rect of the image.
86    float2 uvTextureFgd = fragCoord * uvScaleFgd + uvOffsetFgd;
87    float2 uvTextureBgd = fragCoord * uvScaleBgd + uvOffsetBgd;
88
89    vec4 colorForeground = foreground.eval(uvTextureFgd);
90    vec4 color = background.eval(uvTextureBgd);
91
92    // Add rotation for the rain (as a default sin(time * 0.05) can be used).
93    float variation = wiggle(time - uv.y * 1.1, 0.10);
94    uv = rotateAroundPoint(uv, vec2(0.5, -1.42), variation * PI / 9.);
95
96    // 1. Generate a layer of rain behind the subject.
97    Rain rain = generateRain(
98          uv,
99          screenAspectRatio,
100          time * 18.,
101          /* Grid size = */ vec2(20.0, 2.0),
102          intensity);
103
104    color.rgb = mix(color.rgb, highlightColor, rainVisibility * rain.dropMask);
105
106    // 2. Generate mid layer of rain behind the subject.
107    rain = generateRain(
108          uv,
109          screenAspectRatio,
110          time * 21.4,
111          /* Grid size = */ vec2(30.0, 4.0),
112          intensity);
113
114    // 3. Blend those layers.
115    color.rgb = mix(color.rgb, highlightColor, rainVisibility * rain.dropMask);
116
117    // 4. Blend with the foreground. Any effect from here will be in front of the subject.
118    color.rgb = normalBlend(color.rgb, colorForeground.rgb, colorForeground.a);
119
120    // 5. Draw splashes
121    color.rgb = drawSplashes(uv, fragCoord, color.rgb);
122
123    // 6. Generate a layer of rain in front of the subject (bigger and faster).
124    rain = generateRain(
125          uv,
126          screenAspectRatio,
127          time * 27.,
128          /* Grid size = */ vec2(8.0, 3.0),
129          intensity);
130
131    // Closer rain drops are less visible.
132    color.rgb = mix(color.rgb, highlightColor, 0.7 * rainVisibility * rain.dropMask);
133
134    return color;
135}
136