uniform float opacity;
//uniform float mapScale;
uniform vec3 baseColor;





#if defined use_map
    varying vec2 vUv;
    uniform sampler2D map; 
    uniform vec3 mapColor;
    
    vec4 applyMapColor(vec4 color){ 
        vec2 uv = vUv;
        /*if(mapScale != 1.0){ 
            uv = (vUv - 0.5) / mapScale + 0.5; 
            if(uv.x > 1.0 || uv.y > 1.0 || uv.x < 0.0 || uv.y < 0.0){
                //color = vec4(0.0,0.0,0.0,0.0);
                discard;
            } 
        }*/
        vec4 colorFromMap = texture2D(map, uv);
         
        #if defined mapOverlay
            //贴图叠加在基础色上，而非相乘
            colorFromMap.rgb *= mapColor;
            color = color * (1.0-colorFromMap.a) + colorFromMap;
        #else
            color *= colorFromMap;
             
        #endif
        
        return color;
    }
#endif
 

#if defined(GL_EXT_frag_depth) && defined(useDepth)
    //似乎通过gl.getExtension('EXT_frag_depth')得到的GL_EXT_frag_depth
     
    uniform sampler2D depthTexture;
    
    uniform vec2 resolution;
    uniform vec2 viewportOffset; //  viewportOffset 范围从0-整个画布的像素
    uniform vec3 backColor;
    uniform float occlusionDistance;
    uniform float clipDistance;
    uniform float startClipDis;
    uniform float startOcclusDis;
    uniform float maxClipFactor;
    uniform float maxOcclusionFactor;
    //uniform bool uUseOrthographicCamera;                                    

    
#endif 

#if defined(GL_EXT_frag_depth) && defined(useDepth) || defined(FadeFar) 
    uniform float nearPlane;
    uniform float farPlane; 
    float convertToLinear(float zValue){
        //if(uUseOrthographicCamera){
        //   return zValue*(farPlane-nearPlane)+nearPlane;
        //}else{ 
            float z = zValue * 2.0 - 1.0;
            return (2.0 * nearPlane * farPlane) / (farPlane + nearPlane - z * (farPlane - nearPlane));
        //}      
    } 
#endif

#if defined(FadeFar)
    uniform float fadeFar;
#endif
//#include <clipping_planes_pars_fragment>
  
void main() {
    //#include <clipping_planes_fragment>
    
    vec4 color = vec4(baseColor, opacity);
    
    
    
    #if defined(GL_EXT_frag_depth) && defined(useDepth) || defined(FadeFar)  
       
        float fragDepth = convertToLinear(gl_FragCoord.z);
        
        #if defined(FadeFar) 
            float fadeOutFar = fadeFar * 1.3; //完全消失距离
            if(fragDepth > fadeOutFar){
                discard;
            }else if(fragDepth > fadeFar){
                color.a *= (fadeOutFar - fragDepth) / (fadeOutFar - fadeFar);
                 
            }  
        #endif
        
        
        float mixFactor = 0.0;
        float clipFactor = 0.0;
        
        #if defined(GL_EXT_frag_depth) && defined(useDepth)
        
            vec2 depthTxtCoords = vec2(gl_FragCoord.x-viewportOffset.x,  gl_FragCoord.y - viewportOffset.y) / resolution;
            //gl_FragCoord大小为 viewport client大小 
            
            float textureDepth = convertToLinear(texture2D(depthTexture, depthTxtCoords).r);

           
            float delta =  fragDepth - textureDepth;

            if (delta > 0.0)//差距
            {
                // occlusionDistance and clipDistance define the width of the respective zones and
                // mixFactor and clipFactor express the interpolation between the two colors depending on the position
                // of the current fragment withing those zones.
                
                mixFactor = clamp((delta - startOcclusDis) / (occlusionDistance - startOcclusDis), 0.0, maxOcclusionFactor);
                clipFactor = clamp((delta - startClipDis) / (clipDistance - startClipDis), 0.0, maxClipFactor);
                
                
            } 
         #endif
         
         
        // If the fragment is totally transparent, don't bother drawing it
        if (clipFactor == 1.0)
        {
            discard;
        }else{
            
            #if defined use_map
                color = applyMapColor(color);  
            #endif
             
            #if defined(GL_EXT_frag_depth) && defined(useDepth)
                float r = pow(1.0 - clipFactor, 3.0); //更透明些 
                color = vec4(mix(color.rgb, backColor, mixFactor), color.a * r);
            #endif    
        }
         
         
    #else
        #if defined use_map
            color = applyMapColor(color); 
        #endif 
    #endif
  
    gl_FragColor = color;
  
}