 // vshader
 precision mediump float;
 uniform float deltaT;     //value from application program
 attribute vec4 vPosition; //value from application program
 varying float s;          //value also used in fragment shader
 void main(void)
 {
   s =  sin ( 0.001 * deltaT );  // scaling factor  
   vec4 vPosition1 = vPosition * vec4 ( s, s, s, 1.0 );
   gl_Position = gl_ModelViewProjectionMatrix * vPosition1;
 }

