leaflet 雷达扫描的shader

0.效果：

1.vertexShader

        attribute vec2 aCRSCoords;        
        attribute vec2 aExtrudeCoords;
        uniform mat4 uTransformMatrix;     /
        uniform vec2 uPixelSize;
        uniform float uNow;
        
        attribute float adm0cap;

        varying vec2 vExtrudeCoords;
        
        varying float vTimeNow ;

        varying vec2 vCRSCoords;

        void main(void) {
            vExtrudeCoords = aExtrudeCoords;
            vTimeNow = uNow;

            gl_Position = uTransformMatrix * vec4(aCRSCoords, 1.0, 1.0);
    
            // If not, just place a smaller kitten.
            gl_Position += vec4(aExtrudeCoords * uPixelSize * 100.0, 0.0, 0.0);
            
        }

2.fragmentShader

        uniform sampler2D uTexture0; 


        precision highp float;
        
        varying float vTimeNow ;

        varying vec2 vExtrudeCoords;

        const float PI = 3.1415926535898;


        const float PI_2 = PI/2.0;



        float arctan2(float y,float x){
            if( x > 0.0 )
                return atan(y/x);
            else if( x < 0.0 && y >= 0.0 )
                return atan(y/x) + PI;
            else if( x < 0.0 && y < 0.0 )
                return atan(y/x) - PI;
            else if( x == 0.0 && y > 0.0 )
                return PI_2;
            else if( x == 0.0 && y < 0.0 )
                return -PI_2;
            else return 0.0;
        }

        void main(void) {
            // Our extrude coordinates go from [-1,-1] to [1,1],
            // but the texture lookup needs coords in the [0,0]-[1,1]
            // range.

            vec2 texelCoords;
            texelCoords.x = (vExtrudeCoords.x + 1.0) / 2.0;
            texelCoords.y = (1.0 - vExtrudeCoords.y) / 2.0;
            
            // Perform a texture lookup
            vec4 texelColour = texture2D(uTexture0, texelCoords);

            float angle = arctan2( vExtrudeCoords.y, vExtrudeCoords.x );    

            angle = mod( -vTimeNow/500.0 + angle,  PI * 2.0 );
            float alpha = 0.0;
            if( angle < PI )
                angle = 0.0; 
            else
                alpha = ( angle - PI ) / PI * 1.0;

            if( mod(gl_FragCoord.s,3.0) < 1.0 || mod(gl_FragCoord.t,3.0) < 1.0 )
                alpha = 0.0;
                

            // Use the colour from the texture as the colour for this pixel
            texelColour.a = texelColour.a*alpha;
            gl_FragColor = texelColour;
        }