// VertexPosition is a special function; whatever it returns is what glPosition ends up being.
//	In this toy example, you can just comment this out -- a reasonable one is hard coded in 
function VertexPosition() {  
  	// All varyings are specified via 'varyings.<name>'. Attributes with 'attributes.<name>'
  	// 
	// Currently, you can't use attributes in FragmentColor; you must create a varying for it.
  	// in the future, it might auto-transfer used attributes in the fragment shader into 
    // varyings; it remains to be seen if this is a good idea. 
    varyings.pt = attributes.pt; 
  
  	// uniforms.<name> 
  	var t = uniforms.t;
  
  	// You can return whatever size array/vector; it automatically completes the vector for 
  	// you with all 0's, except for 1 as the last element.
    return [Math.cos(t) * attributes.pt[0] + Math.sin(t) * attributes.pt[1], 
            Math.sin(t) * attributes.pt[0] - Math.cos(t) * attributes.pt[1] ]; 
};

/** FragmentColor is a special function; it tries to resolve to a vector and that is 
	what is used to set the fragment color */    
function FragmentColor() { 
  	var x = varyings.pt[0];
    var y = varyings.pt[1];  	
  	  	
  	var t = (x * y > 0) ? uniforms.t : uniforms.t * 2; 
  
    // A handful of Math.x functions are mapped to the GLSL equivalents
    var dist = Math.sqrt(x*x + y*y);
    var threshold = Math.abs(Math.cos(t));
    var rim = .01;
    if(dist > (threshold-rim) && dist <  (threshold+rim)) {
      	// Returning nothing in a FragmentColor function
        // is equivalent to performing a GLSL 'discard' -- it 
      	// simply does nothing with the fragment
    	return;
    }
    if(dist > threshold){
    	return [fmod(x, 1.0), fmod(y, 1.0), 0.5*(Math.cos(t)+1.0)];
    }  	
  	// FragmentColor, like VertexPosition, will fill out the vec4 for you if you
  	// dont. You do have to be consistent though -- Since we returned a vector of 3
  	// above, we have to here. Otherwise it is a type error. For example:
  	// return [1, 1, 1, 1]; // wont work. 
    return [0.5*(x+1.0), 0.5*(y+1.0) , 0.5*(Math.cos(t)+1.0)]; 
};

/** Functions you define automatically get pulled in if they are used */
function fmod(a,b) { return a - (Math.floor(a / b) * b); };