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// Copyright 2021, 2022 Benjamin Barenblat
//
// 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
//
// https://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.
#version 150
// The color of sunlight (5800 K) in sRGB.
const vec4 kSunColor = vec4(1.0, 0.9411765, 0.9137255, 1.0);
in vec3 model_cartesian_position; // unit vector pointing toward current point
in vec2 texture_coordinate;
uniform sampler2D planet;
uniform sampler2D clouds;
uniform vec3 sun_direction; // unit vector pointing toward sun
out vec4 out_color;
void main() {
// Compute diffuse illumination from the Sun. We assume all rays are parallel,
// which isn't true, but at Earth scales, it causes a maximum error of about
// 0.003 degrees, well within our error budget.
float diffuse = max(dot(model_cartesian_position, sun_direction), 0.0);
// The planet is a mixture of the ground texture and the cloud texture. Assume
// clouds reflect sunlight; the ground texture needs no color adjustment,
// since it's already colored as if being hit by sunlight.
out_color = diffuse * mix(texture(planet, texture_coordinate), kSunColor,
texture(clouds, texture_coordinate).r);
}
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