Twitter avatar experiment 3.php

<?php

	/*
	
		Image based on overlapping circle arcs
		
		SDDS 1st Jun 2014
	
	*/

	// draw parameters
	define('NUM_RINGS', '8');
	define('BASE_ALPHA', '120'); // 0 is opaque, 127 is transparent
	define('IMG_WIDTH', '500');
	define('IMG_HEIGHT', '500');

	// top left, bottom left, bottom right, top right
	$points = array(array(0,0), array(0,IMG_HEIGHT), array(IMG_WIDTH,IMG_HEIGHT), array(IMG_WIDTH,0));

	// helper functions
	function HuetoRGB( $v1, $v2, $vH )
	{
	    if ( $vH < 0 )
	    {
	        $vH += 1;
	    }
	    if ( $vH > 1 )
	    {
	        $vH -= 1;
	    }
	    if ( ( 6 * $vH ) < 1 )
	    {
	        return ( $v1 + ( $v2 - $v1 ) * 6 * $vH );
	    }
	    if ( ( 2 * $vH ) < 1 )
	    {
	        return ( $v2 );
	    }
	    if ( ( 3 * $vH ) < 2 )
	    {
	        return ( $v1 + ( $v2 - $v1 ) * ( ( 2 / 3 ) - $vH ) * 6 );
	    }
	    return ( $v1 );
	}

	function HSLtoRGB ( $H, $S, $L )
	{
	    if ( $S == 0 )
	    {
	        $R = $L * 255;
	        $G = $L * 255;
	        $B = $L * 255;
	    }
	    else
	    {
	        if ( $L < 0.5 )
	        {
	            $var_2 = $L * ( 1 + $S );
	        }
	        else
	        {
	            $var_2 = ( $L + $S ) - ( $S * $L );
	        }
	        $var_1 = 2 * $L - $var_2;
	        $R = 255 * HuetoRGB( $var_1, $var_2, $H + ( 1 / 3 ) );
	        $G = 255 * HuetoRGB( $var_1, $var_2, $H );
	        $B = 255 * HuetoRGB( $var_1, $var_2, $H - ( 1 / 3 ) );
	    }
	    return array( $R, $G, $B );
	}	

	// create a white image with alpha, blending and AA
	$img = imagecreatetruecolor( IMG_WIDTH, IMG_HEIGHT );
	$background = imagecolorallocate( $img, 255, 255, 255);
	imagefill($img, 0, 0, $background);
	imagealphablending( $img, true );
	imagesavealpha($img, true);
	imageantialias($img, true);
	
	// for each point...	
	foreach ($points as $point) {
		// random hue (0..1), then get RGB value of that and assign to a colour
		$hue = mt_rand() / mt_getrandmax();
		list($redVal, $greenVal, $blueVal) = HSLtoRGB($hue, 1.0, 0.5);
		$colour = imagecolorallocatealpha($img, $redVal, $greenVal, $blueVal, BASE_ALPHA);

		// draw several overlapping circle of increasing radius from this point
		for ($i = 1; $i <= NUM_RINGS; $i++) {
	    	imagefilledellipse($img, $point[0], $point[1], 2*$i*IMG_WIDTH/NUM_RINGS, 2*$i*IMG_HEIGHT/NUM_RINGS,  $colour);	
		}	
	}
		
	// output the image as a PNG
	header( "Content-type: image/png" );
	imagepng( $img );
	imagedestroy( $img );
?>