前言
当我们使用官网的例子设置天空盒后，会发现天空云彩是斜的，比如下边这张图：
通过查阅网上资料，需要修改cesium的源码，以下是修改后skybox的源码，在自己的项目中引入即可：
实现代码
const BoxGeometry = Cesium.BoxGeometry;
const Cartesian3 = Cesium.Cartesian3;
const defaultValue = Cesium.defaultValue;
const defined = Cesium.defined;
const destroyObject = Cesium.destroyObject;
const DeveloperError = Cesium.DeveloperError;
const GeometryPipeline = Cesium.GeometryPipeline;
const Matrix3 = Cesium.Matrix3;
const Matrix4 = Cesium.Matrix4;
const Transforms = Cesium.Transforms;
const VertexFormat = Cesium.VertexFormat;
const BufferUsage = Cesium.BufferUsage;
const CubeMap = Cesium.CubeMap;
const DrawCommand = Cesium.DrawCommand;
const loadCubeMap = Cesium.loadCubeMap;
const RenderState = Cesium.RenderState;
const VertexArray = Cesium.VertexArray;
const BlendingState = Cesium.BlendingState;
const SceneMode = Cesium.SceneMode;
const ShaderProgram = Cesium.ShaderProgram;
const ShaderSource = Cesium.ShaderSource;
//片元着色器，直接从源码复制
const SkyBoxFS = "uniform samplerCube u_cubeMap;\n\
varying vec3 v_texCoord;\n\
void main()\n\
{\n\
vec4 color = textureCube(u_cubeMap, normalize(v_texCoord));\n\
gl_FragColor = vec4(czm_gammaCorrect(color).rgb, czm_morphTime);\n\
}\n\
";
//顶点着色器有修改，主要是乘了一个旋转矩阵
const SkyBoxVS = "attribute vec3 position;\n\
varying vec3 v_texCoord;\n\
uniform mat3 u_rotateMatrix;\n\
void main()\n\
{\n\
vec3 p = czm_viewRotation * u_rotateMatrix * (czm_temeToPseudoFixed * (czm_entireFrustum.y * position));\n\
gl_Position = czm_projection * vec4(p, 1.0);\n\
v_texCoord = position.xyz;\n\
}\n\
";
/**
/**
* A sky box around the scene to draw stars. The sky box is defined using the True Equator Mean Equinox (TEME) axes.
* <p>
* This is only supported in 3D. The sky box is faded out when morphing to 2D or Columbus view. The size of
* the sky box must not exceed {@link Scene#maximumCubeMapSize}.
* </p>
*
* @alias SkyBox
* @constructor
*
* @param {Object} options Object with the following properties:
* @param {Object} [options.sources] The source URL or <code>Image</code> object for each of the six cube map faces. See the example below.
* @param {Boolean} [options.show=true] Determines if this primitive will be shown.
*
*
* @example
* scene.skyBox = new Cesium.SkyBox({
* sources : {
* positiveX : 'skybox_px.png',
* negativeX : 'skybox_nx.png',
* positiveY : 'skybox_py.png',
* negativeY : 'skybox_ny.png',
* positiveZ : 'skybox_pz.png',
* negativeZ : 'skybox_nz.png'
* }
* });
*
* @see Scene#skyBox
* @see Transforms.computeTemeToPseudoFixedMatrix
*/
function SkyBox(options) {
/**
* The sources used to create the cube map faces: an object
* with <code>positiveX</code>, <code>negativeX</code>, <code>positiveY</code>,
* <code>negativeY</code>, <code>positiveZ</code>, and <code>negativeZ</code> properties.
* These can be either URLs or <code>Image</code> objects.
*
* @type Object
* @default undefined
*/
this.sources = options.sources;
this._sources = undefined;
/**
* 是否开启近地模式
*/
this.nearGround = options.nearGround;
/**
* Determines if the sky box will be shown.
*
* @type {Boolean}
* @default true
*/
this.show = defaultValue(options.show, true);
this._command = new DrawCommand({
modelMatrix: Matrix4.clone(Matrix4.IDENTITY),
owner: this,
});
this._cubeMap = undefined;
this._attributeLocations = undefined;
this._useHdr = undefined;
}
/**
* Called when {@link Viewer} or {@link CesiumWidget} render the scene to
* get the draw commands needed to render this primitive.
* <p>
* Do not call this function directly. This is documented just to
* list the exceptions that may be propagated when the scene is rendered:
* </p>
*
* @exception {DeveloperError} this.sources is required and must have positiveX, negativeX, positiveY, negativeY, positiveZ, and negativeZ properties.
* @exception {DeveloperError} this.sources properties must all be the same type.
*/
SkyBox.prototype.update = function (frameState, useHdr) {
const that = this;
if (!this.show) {
return undefined;
}
if (
frameState.mode !== SceneMode.SCENE3D &&
frameState.mode !== SceneMode.MORPHING
) {
return undefined;
}
// The sky box is only rendered during the render pass; it is not pickable, it doesn't cast shadows, etc.
if (!frameState.passes.render) {
return undefined;
}
const context = frameState.context;
if (this._sources !== this.sources) {
this._sources = this.sources;
const sources = this.sources;
//>>includeStart('debug', pragmas.debug);
if (
!defined(sources.positiveX) ||
!defined(sources.negativeX) ||
!defined(sources.positiveY) ||
!defined(sources.negativeY) ||
!defined(sources.positiveZ) ||
!defined(sources.negativeZ)
) {
throw new DeveloperError(
"this.sources is required and must have positiveX, negativeX, positiveY, negativeY, positiveZ, and negativeZ properties."
);
}
if (
typeof sources.positiveX !== typeof sources.negativeX ||
typeof sources.positiveX !== typeof sources.positiveY ||
typeof sources.positiveX !== typeof sources.negativeY ||
typeof sources.positiveX !== typeof sources.positiveZ ||
typeof sources.positiveX !== typeof sources.negativeZ
) {
throw new DeveloperError(
"this.sources properties must all be the same type."
);
}
//>>includeEnd('debug');
if (typeof sources.positiveX === "string") {
// Given urls for cube-map images. Load them.
loadCubeMap(context, this._sources).then(function (cubeMap) {
that._cubeMap = that._cubeMap && that._cubeMap.destroy();
that._cubeMap = cubeMap;
});
} else {
this._cubeMap = this._cubeMap && this._cubeMap.destroy();
this._cubeMap = new CubeMap({
context: context,
source: sources,
});
}
}
const command = this._command;
if (!defined(command.vertexArray)) {
command.uniformMap = {
u_cubeMap: function () {
return that._cubeMap;
},
u_rotateMatrix: function () {
return that.nearGround ? (command.modelMatrix = Transforms.eastNorthUpToFixedFrame(frameState.camera._positionWC),
Matrix4.getMatrix3(command.modelMatrix, new Matrix3)) : Matrix3.IDENTITY;
}
};
const geometry = BoxGeometry.createGeometry(
BoxGeometry.fromDimensions({
dimensions: new Cartesian3(2.0, 2.0, 2.0),
vertexFormat: VertexFormat.POSITION_ONLY,
})
);
const attributeLocations = (this._attributeLocations = GeometryPipeline.createAttributeLocations(
geometry
));
command.vertexArray = VertexArray.fromGeometry({
context: context,
geometry: geometry,
attributeLocations: attributeLocations,
bufferUsage: BufferUsage.STATIC_DRAW,
});
command.renderState = RenderState.fromCache({
blending: BlendingState.ALPHA_BLEND,
});
}
if (!defined(command.shaderProgram) || this._useHdr !== useHdr) {
const fs = new ShaderSource({
defines: [useHdr ? "HDR" : ""],
sources: [SkyBoxFS],
});
command.shaderProgram = ShaderProgram.fromCache({
context: context,
vertexShaderSource: SkyBoxVS,
fragmentShaderSource: fs,
attributeLocations: this._attributeLocations,
});
this._useHdr = useHdr;
}
if (!defined(this._cubeMap)) {
return undefined;
}
return command;
};
/**
* Returns true if this object was destroyed; otherwise, false.
* <br /><br />
* If this object was destroyed, it should not be used; calling any function other than
* <code>isDestroyed</code> will result in a {@link DeveloperError} exception.
*
* @returns {Boolean} <code>true</code> if this object was destroyed; otherwise, <code>false</code>.
*
* @see SkyBox#destroy
*/
SkyBox.prototype.isDestroyed = function () {
return false;
};
/**
* Destroys the WebGL resources held by this object. Destroying an object allows for deterministic
* release of WebGL resources, instead of relying on the garbage collector to destroy this object.
* <br /><br />
* Once an object is destroyed, it should not be used; calling any function other than
* <code>isDestroyed</code> will result in a {@link DeveloperError} exception. Therefore,
* assign the return value (<code>undefined</code>) to the object as done in the example.
*
* @exception {DeveloperError} This object was destroyed, i.e., destroy() was called.
*
*
* @example
* skyBox = skyBox && skyBox.destroy();
*
* @see SkyBox#isDestroyed
*/
SkyBox.prototype.destroy = function () {
const command = this._command;
command.vertexArray = command.vertexArray && command.vertexArray.destroy();
command.shaderProgram =
command.shaderProgram && command.shaderProgram.destroy();
this._cubeMap = this._cubeMap && this._cubeMap.destroy();
return destroyObject(this);
};
export default SkyBox;
修改代码的关键点：
1、添加近地属性，方便扩展
//......
function SkyBox(options) {
this.sources = options.sources;
this._sources = undefined;
/**
* 是否开启近地模式
*/
this.nearGround = options.nearGround;
//......
}
2、修改顶点着色器
//顶点着色器有修改，主要是乘了一个旋转矩阵
const SkyBoxVS = "attribute vec3 position;\n\
varying vec3 v_texCoord;\n\
uniform mat3 u_rotateMatrix;\n\
void main()\n\
{\n\
vec3 p = czm_viewRotation * u_rotateMatrix * (czm_temeToPseudoFixed * (czm_entireFrustum.y * position));\n\
gl_Position = czm_projection * vec4(p, 1.0);\n\
v_texCoord = position.xyz;\n\
}\n\
";
/**
3、修改command.uniformMap
command.uniformMap = {
u_cubeMap: function () {
return that._cubeMap;
},
u_rotateMatrix: function () {
return that.nearGround ? (command.modelMatrix = Transforms.eastNorthUpToFixedFrame(frameState.camera._positionWC),
Matrix4.getMatrix3(command.modelMatrix, new Matrix3)) : Matrix3.IDENTITY;
}
};
使用
import { default as SkyBox } from "@/lib/cesium/sky-SkyBox"
// 定义
const blueSkySkybox = new SkyBox({
sources: {
positiveX: fileUtil.getAssetsFile("skybox/blueSky/Right.jpg"),
negativeX: fileUtil.getAssetsFile("skybox/blueSky/Left.jpg"),
positiveY: fileUtil.getAssetsFile("skybox/blueSky/Front.jpg"),
negativeY: fileUtil.getAssetsFile("skybox/blueSky/Back.jpg"),
positiveZ: fileUtil.getAssetsFile("skybox/blueSky/Up.jpg"),
negativeZ: fileUtil.getAssetsFile("skybox/blueSky/Down.jpg")
},
nearGround: true
})
// 使用
viewer.scene.postRender.addEventListener(function () {
const e = viewer.camera.position;
if (Cesium.Cartographic.fromCartesian(e).height < 2000) {
viewer.scene.skyBox.nearGround = true;
viewer.scene.skyBox = blueSkySkybox;
viewer.scene.skyAtmosphere.show = false;
} else {
viewer.scene.skyBox = defaultSkyBox;
viewer.scene.skyAtmosphere.show = true;
}
});