Cesium后处理postProcessStages特效

1，边缘检测（天际线）createEdgeDetectionStage

var collection = viewer.scene.postProcessStages;

        var edgeDetection = Cesium.PostProcessStageLibrary.createEdgeDetectionStage();

        var postProccessStage = new Cesium.PostProcessStage({
            name: 'czm_skylinetemp',
            fragmentShader: 'uniform sampler2D colorTexture;' +
                'uniform sampler2D depthTexture;' +

                'varying vec2 v_textureCoordinates;' +

                'void main(void)' +
                '{' +
                'float depth = czm_readDepth(depthTexture, v_textureCoordinates);' +
                'vec4 color = texture2D(colorTexture, v_textureCoordinates);' +
                'if(depth<1.0 - 0.000001){'+
                'gl_FragColor = color;' +
                '}'+