I am using Three.js as a framework for developing a space simulator and I am trying, but failing to get night lights working.
The simulator can be accessed here:
and a page running the code snippet below can be found here:
orbitingeden.com/orrery/soloearth.html
The code for the sample page is here. I don't even know where to begin. I tried rendering two globes a few units apart, one closer to the sun (daytime version) and one further(nighttime version) but there are many problems, not the least of which is that they begin to overlap each other in strange dodecahedron kind of ways. I adopted the tDiffuse2 idea from this orrery, but couldn't get it working.
<!doctype html>
<html lang="en">
<head>
<title>three.js webgl - earth</title>
<meta charset="utf-8">
<script src="three.js/Detector.js"></script>
<script src="three.js/Three.js"></script>
</head>
<body>
<script>
if ( ! Detector.webgl ) Detector.addGetWebGLMessage();
var radius = 6371;
var tilt = 0.41;
var rotationSpeed = 0.02;
var cloudsScale = 1.005;
var SCREEN_HEIGHT = window.innerHeight;
var SCREEN_WIDTH = window.innerWidth;
var container, camera, scene, renderer;
var meshPlanet, meshClouds, dirLight, ambientLight;
var clock = new THREE.Clock();
init();
animate();
function init() {
container = document.createElement( 'div' );
document.body.appendChild( container );
scene = new THREE.Scene();
scene.fog = new THREE.FogExp2( 0x000000, 0.00000025 );
camera = new THREE.PerspectiveCamera( 25, SCREEN_WIDTH / SCREEN_HEIGHT, 50, 1e7 );
camera.position.z = radius * 5;
scene.add( camera );
dirLight = new THREE.DirectionalLight( 0xffffff );
dirLight.position.set( -20, 0, 2 ).normalize();
scene.add( dirLight );
ambientLight = new THREE.AmbientLight( 0x000000 );
scene.add( ambientLight );
//initialize the earth
var planetTexture = THREE.ImageUtils.loadTexture( "textures/earth-day.jpg" ),
nightTexture = THREE.ImageUtils.loadTexture( "textures/earthNight.gif" ),
cloudsTexture = THREE.ImageUtils.loadTexture( "textures/clouds.gif" ),
normalTexture = THREE.ImageUtils.loadTexture( "textures/earth-map.jpg" ),
specularTexture = THREE.ImageUtils.loadTexture( "textures/earth-specular.jpg" );
var shader = THREE.ShaderUtils.lib[ "normal" ];
var uniforms = THREE.UniformsUtils.clone( shader.uniforms );
uniforms[ "tNormal" ].texture = normalTexture;
uniforms[ "uNormalScale" ].value = 0.85;
uniforms[ "tDiffuse" ].texture = planetTexture;
uniforms[ "tDiffuse2" ].texture = nightTexture;
uniforms[ "tSpecular" ].texture = specularTexture;
uniforms[ "enableAO" ].value = false;
uniforms[ "enableDiffuse" ].value = true;
uniforms[ "enableSpecular" ].value = true;
uniforms[ "uDiffuseColor" ].value.setHex( 0xffffff );
uniforms[ "uSpecularColor" ].value.setHex( 0x333333 );
uniforms[ "uAmbientColor" ].value.setHex( 0x000000 );
uniforms[ "uShininess" ].value = 15;
var parameters = {
fragmentShader: shader.fragmentShader,
vertexShader: shader.vertexShader,
uniforms: uniforms,
lights: true,
fog: true
};
var materialNormalMap = new THREE.ShaderMaterial( parameters );
geometry = new THREE.SphereGeometry( radius, 100, 50 );
geometry.computeTangents();
meshPlanet = new THREE.Mesh( geometry, materialNormalMap );
meshPlanet.rotation.y = 0;
meshPlanet.rotation.z = tilt;
scene.add( meshPlanet );
// clouds
var materialClouds = new THREE.MeshLambertMaterial( { color: 0xffffff, map: cloudsTexture, transparent: true } );
meshClouds = new THREE.Mesh( geometry, materialClouds );
meshClouds.scale.set( cloudsScale, cloudsScale, cloudsScale );
meshClouds.rotation.z = tilt;
scene.add( meshClouds );
renderer = new THREE.WebGLRenderer( { clearColor: 0x000000, clearAlpha: 1 } );
renderer.setSize( SCREEN_WIDTH, SCREEN_HEIGHT );
renderer.sortObjects = false;
renderer.autoClear = false;
container.appendChild( renderer.domElement );
};
function animate() {
requestAnimationFrame( animate );
render();
};
function render() {
// rotate the planet and clouds
var delta = clock.getDelta();
meshPlanet.rotation.y += rotationSpeed * delta;
meshClouds.rotation.y += 1.25 * rotationSpeed * delta;
//render the scene
renderer.clear();
renderer.render( scene, camera );
};
</script>
</body>
</html>
If I understand your question....
I don't know three.js but in general I'd do this by having a shader that has gets passed both the day and night time textures and then selecting one or the other in the shader. For example
uniform sampler2D dayTexture;
uniform sampler2D nightTexture;
varying vec3 v_surfaceToLight; // assumes this gets passed in from vertex shader
varying vec4 v_normal; // assumes this gets passed in from vertex shader
varying vec2 v_texCoord; // assumes this gets passed in from vertex shader
void main () {
vec3 normal = normalize(v_normal);
vec3 surfaceToLight = normalize(v_surfaceToLight);
float angle = dot(normal, surfaceToLight);
vec4 dayColor = texture2D(dayTexture, v_texCoords);
vec4 nightColor = texture2D(nightTexture, v_texCoord);
vec4 color = angle < 0.0 ? dayColor : nightColor;
...
gl_FragColor = color * ...;
}
Basically you take the lighting calculation and instead of using it for lighting you use it to select the texture. A lighting calculation usually uses a dot product between the normal of the surface and the direction of the light (the sun) from the surface. That gives you the cosine of the angle between those to vectors. Cosine goes from -1 to 1 so if the value is from -1 to 0 it's facing away from the sun, if it's 0 to +1 it's facing toward the sun.
The line
vec4 color = angle < 0.0 ? dayColor : nightColor;
selects the day or night. That's going to be a harsh cutoff. You might experiment with something more fuzzy like
// convert from -1 <-> +1 to 0 <-> +1
float lerp0To1 = angle * 0.5 + 0.5;
// mix between night and day
vec4 color = mix(nightColor, dayColor, lerp0to1);
That would give you 100% day on the spot directly facing the sun and 100% night on the spot directly opposite the sun and a mix in-between. Probably not what you want but you can futs with the numbers. For example
// sharpen the mix
angle = clamp(angle * 10.0, -1.0, 1.0);
// convert from -1 <-> +1 to 0 <-> +1
float lerp0To1 = angle * 0.5 + 0.5;
// mix between night and day
vec4 color = mix(nightColor, dayColor, lerp0to1);
Hopefully that made sense.
So I spent a little time working up a Three.js example, partly to learn Three.js. The sample is here.
The shader I used is this
uniform sampler2D dayTexture;
uniform sampler2D nightTexture;
uniform vec3 sunDirection;
varying vec2 vUv;
varying vec3 vNormal;
void main( void ) {
vec3 dayColor = texture2D( dayTexture, vUv ).rgb;
vec3 nightColor = texture2D( nightTexture, vUv ).rgb;
// compute cosine sun to normal so -1 is away from sun and +1 is toward sun.
float cosineAngleSunToNormal = dot(normalize(vNormal), sunDirection);
// sharpen the edge beween the transition
cosineAngleSunToNormal = clamp( cosineAngleSunToNormal * 10.0, -1.0, 1.0);
// convert to 0 to 1 for mixing
float mixAmount = cosineAngleSunToNormal * 0.5 + 0.5;
// Select day or night texture based on mixAmount.
vec3 color = mix( nightColor, dayColor, mixAmount );
gl_FragColor = vec4( color, 1.0 );
// comment in the next line to see the mixAmount
//gl_FragColor = vec4( mixAmount, mixAmount, mixAmount, 1.0 );
}
The big difference from the one above is that since the sun is generally considered a directional light since it is so far away then all you need is it's direction. In other words, which way it's pointing relative to the earth.
此内容由惯性聚合(RSS阅读器)自动聚合整理，仅供阅读参考。 原文来自 — 版权归原作者所有。