sphere.psvg

<!-- sphere.psvg               -->
<!-- 3D animated shaded sphere -->

<psvg width="400" height="400" background="black">
  <var N="12"
       M="12"
       R="1"
       T="4"
       FOCAL="400"
  />
  
  <stroke color="black"/>
    
  <!-- generate UV sphere vertices --> 
  <var pts=""/>
  <for i="0" true="{i<N}" step="1">
  	<for j="0" true="{j<M}" step="1">
      <var th="{PI*2*j/M}"
           ph="{PI*(i/(N-1)-0.5)}"
           x="{R*COS(th)*COS(ph)}"
      	   y="{R*SIN(ph)}"
           z="{R*SIN(th)*COS(ph)}"
      />
      <asgn pts="{CAT(pts,x,y,z)}"/>
    </for>
  </for>
    
  <!-- project 3D points to 2D coordinates--> 
  <def-projection pts="" th="0" ph="{PI/4}">
    <var qts=""/>
    <for i="0" true="{i<N*N}" step="1">
      <var x="{NTH(pts,i*3)}" y="{NTH(pts,i*3+1)}" z="{NTH(pts,i*3+2)}"/>
      <var x1="{x*COS(th)-z*SIN(th)}" z1="{x*SIN(th)+z*COS(th)}"/>
      <var y2="{y*COS(ph)-z1*SIN(ph)}" z2="{y*SIN(ph)+z1*COS(ph)}"/>
      
      <asgn x="{x1}" y="{y2}" z="{z2}"/>
      <asgn z="{z+R*3}"/>
      <var px="{FOCAL*x/z+WIDTH/2}"/>
      <var py="{FOCAL*y/z+HEIGHT/2}"/>
     
      <asgn qts="{CAT(qts,px,py,(z-R*2)/(R*2))}"/>
    </for>
    <return value="{qts}"/>
  </def-projection>
  
  <!-- build the animation --> 
  
  <var qts=""/>
  <for t="0" true="{t<T}" step="1">
    <asgn qts="{CAT(qts,projection(pts,(2*PI/M)*t/(T-1)))}"/>
  </for>
  

  <!-- draw each quad --> 
  
  <for i="0" true="{i<N-1}" step="1">
  	<for j="0" true="{j<M}" step="1">
    <polygon id="{i*N*3+j*3}" style="mix-blend-mode:lighten">
      <var row=""/>
      <var ord=""/>
      
      <for t="0" true="{t<T}" step="1">
      	<var j1="{(j+1)%M}"/>
        <asgn row="{CAT(row,NTH(qts,t*N*M*3+i*M*3+j*3))}"/>
        <asgn row="{CAT(row,NTH(qts,t*N*M*3+i*M*3+j*3+1))}"/>
        <asgn row="{CAT(row,NTH(qts,t*N*M*3+i*M*3+j1*3))}"/>
        <asgn row="{CAT(row,NTH(qts,t*N*M*3+i*M*3+j1*3+1))}"/>
        <asgn row="{CAT(row,NTH(qts,t*N*M*3+(i+1)*M*3+j1*3))}"/>
        <asgn row="{CAT(row,NTH(qts,t*N*M*3+(i+1)*M*3+j1*3+1))}"/>
        <asgn row="{CAT(row,NTH(qts,t*N*M*3+(i+1)*M*3+j*3))}"/>
        <asgn row="{CAT(row,NTH(qts,t*N*M*3+(i+1)*M*3+j*3+1))}"/>
        <asgn row="{CAT(row,';')}"/>

        <var gray="{FLOOR(MAX(0,255-500*NTH(qts,t*N*M*3+i*M*3+j*3+2)))}"/>
        <var col="rgb({gray}&#44;{gray}&#44;{gray});"/>
        <asgn ord="{CAT(ord,col)}"/>
      </for>
      
    
      <animate 
        attributeName="points" 
        values="{row}" 
        dur="1s" 
        repeatCount="indefinite"/>
      <animate 
        attributeName="fill" 
        values="{ord}" 
        dur="1s" 
        repeatCount="indefinite"/>
      
      </polygon>
      
    </for>
  </for>

  
</psvg>