<?php
    //
    // clock.php3 -- shows the current time as a PNG-image
    // Copyright (C) 2000, Frank Buß, fb@frank-buss.de
    //
    // This software is provided 'as-is', without any express or implied
    // warranty.  In no event will the author be held liable for any damages
    // arising from the use of this software.
    //
    // Permission is granted to anyone to use this software for any purpose,
    // including commercial applications, and to alter it and redistribute it
    // freely.
    //
    function set_4pixel($r, $g, $b, $x, $y)
    {
	global $sx, $sy, $pixels;

	$ofs = 3 * ($sx * $y + $x);
	$pixels[$ofs] = chr($r);
	$pixels[$ofs + 1] = chr($g);
	$pixels[$ofs + 2] = chr($b);
	$pixels[$ofs + 3] = chr($r);
	$pixels[$ofs + 4] = chr($g);
	$pixels[$ofs + 5] = chr($b);
	$ofs += 3 * $sx;
	$pixels[$ofs] = chr($r);
	$pixels[$ofs + 1] = chr($g);
	$pixels[$ofs + 2] = chr($b);
	$pixels[$ofs + 3] = chr($r);
	$pixels[$ofs + 4] = chr($g);
	$pixels[$ofs + 5] = chr($b);
    }
        
    function draw2digits($x, $y, $number)
    {
	draw_digit($x, $y, (int) ($number / 10));
	draw_digit($x + 11, $y, $number % 10);
    }
        
    function draw_digit($x, $y, $digit)
    {
	global $sx, $sy, $pixels, $digits, $lines;
            
	$digit = $digits[$digit];
	$m = 8;
	for ($b = 1, $i = 0; $i < 7; $i++, $b *= 2) {
	    if (($b & $digit) == $b) {
		$j = $i * 4;
		$x0 = $lines[$j] * $m + $x;
		$y0 = $lines[$j + 1] * $m + $y;
		$x1 = $lines[$j + 2] * $m + $x;
		$y1 = $lines[$j + 3] * $m + $y;
		if ($x0 == $x1) {
		    $ofs = 3 * ($sx * $y0 + $x0);
		    for ($h = $y0; $h <= $y1; $h++, $ofs += 3 * $sx) {
			$pixels[$ofs] = chr(0);
			$pixels[$ofs + 1] = chr(0);
			$pixels[$ofs + 2] = chr(0);
		    }
		} else {
		    $ofs = 3 * ($sx * $y0 + $x0);
		    for ($w = $x0; $w <= $x1; $w++) {
			$pixels[$ofs++] = chr(0);
			$pixels[$ofs++] = chr(0);
			$pixels[$ofs++] = chr(0);
		    }
		}
	    }
	}
    }
        
    // create a chunk with the bytes in $data and the specified
    // type and add it to $result
    function add_chunk($type)
    {
	global $result, $data, $chunk, $crc_table;

	// chunk layout:
	// length: 4 bytes: counting chunk data only
	// chunk type: 4 bytes
	// chunk data: length bytes
	// CRC: 4 bytes: CRC-32 checksum of the type and the data
	    
	// copy data and create CRC checksum
	$len = strlen($data);
	$chunk = pack("c*", ($len >> 24) & 255,
		($len >> 16) & 255,
		($len >> 8) & 255,
		$len & 255);
	$chunk .= $type;
	$chunk .= $data;

	// calculate a CRC checksum with the bytes chunk[4..len-1]
	$z = 16777215;
	$z |= 255 << 24;
	$c = $z;
	for ($n = 4; $n < strlen($chunk); $n++) {
	    $c8 = ($c >> 8) & 0xffffff;
	    $c = $crc_table[($c ^ ord($chunk[$n])) & 0xff] ^ $c8;
	}
	$crc = $c ^ $z;

	$chunk .= chr(($crc >> 24) & 255);
	$chunk .= chr(($crc >> 16) & 255);
	$chunk .= chr(($crc >> 8) & 255);
	$chunk .= chr($crc & 255);

	// add it to the result
	$result .= $chunk;
    }


    // ============
    // main program
    // ============

    $sx = 80;
    $sy = 21;
    $pixels = "";
            
    // create filling
    for ($h = 0; $h < $sy; $h++) {
	for ($w = 0; $w < $sx; $w++) {
	    $r = 100 / $sx * $w + 155;
	    $g = 100 / $sy * $h + 155;
	    $b = 255 - (100 / ($sx + $sy) * ($w + $h));
	    $pixels .= chr($r);
	    $pixels .= chr($g);
	    $pixels .= chr($b);
	}
    }
	    
    $date = getdate();
    $s = $date["seconds"];
    $m = $date["minutes"];
    $h = $date["hours"];
    $digits = array(95, 5, 118, 117, 45, 121, 123, 69, 127, 125);
    $lines = array(1, 1, 1, 2, 0, 1, 0, 2, 1, 0, 1, 1, 0, 0, 0, 1, 0, 2, 1, 2, 0, 1, 1, 1, 0, 0, 1, 0);
	    
    draw2digits(4, 2, $h);
    draw2digits(30, 2, $m);
    draw2digits(56, 2, $s);
    set_4pixel(0, 0, 0, 26, 7);
    set_4pixel(0, 0, 0, 26, 13);
    set_4pixel(0, 0, 0, 52, 7);
    set_4pixel(0, 0, 0, 52, 13);

    // create crc-table
    $z = -306674912;  // = 0xedb88320
    for ($n = 0; $n < 256; $n++) {
        $c = $n;
        for ($k = 0; $k < 8; $k++) {
            $c2 = ($c >> 1) & 0x7fffffff;
            if ($c & 1) $c = $z ^ ($c2); else $c = $c2;
        }
        $crc_table[$n] = $c;
    }

    // PNG file signature
    $result = pack("c*", 137,80,78,71,13,10,26,10);
	    
    // IHDR chunk data:
    //   width:              4 bytes
    //   height:             4 bytes
    //   bit depth:          1 byte (8 bits per RGB value)
    //   color type:         1 byte (2 = RGB)
    //   compression method: 1 byte (0 = deflate/inflate)
    //   filter method:      1 byte (0 = adaptive filtering)
    //   interlace method:   1 byte (0 = no interlace)
    $data = pack("c*", ($sx >> 24) & 255,
	($sx >> 16) & 255,
	($sx >> 8) & 255,
	$sx & 255,
	($sy >> 24) & 255,
	($sy >> 16) & 255,
	($sy >> 8) & 255,
	$sy & 255,
	8,
	2,
	0,
	0,
	0);
    add_chunk("IHDR");

    // IDAT: image data:
    //    scanline:
    //        filter byte: 0 = none
    //        RGB bytes for the line
    //    the scanline is compressed with "zlib", method 8 (RFC-1950):
    //        compression method/flags code: 1 byte ($78 = method 8, 32k window)
    //        additional flags/check bits:   1 byte ($01: FCHECK = 1, FDICT = 0, FLEVEL = 0)
    //        compressed data blocks:        n bytes
    //            one block (RFC-1951):
    //                bit 0: BFINAL: 1 for the last block
    //                bit 1 and 2: BTYPE: 0 for no compression
    //                next 2 bytes: LEN (LSB first)
    //                next 2 bytes: one's complement of LEN
    //                LEN bytes uncompressed data
    //        check value:  4 bytes (Adler-32 checksum of the uncompressed data)
    //
    $len = ($sx * 3 + 1) * $sy;
    $data = pack("c*", 0x78, 0x01,
        1,
	$len & 255,
	($len >> 8) & 255,
	255 - ($len & 255),
	255 - (($len >> 8) & 255));
    $start = strlen($data);
    $i2 = 0;
    for ($h = 0; $h < $sy; $h++) {
	$data .= chr(0);
	for ($w = 0; $w < $sx * 3; $w++) {
	    $data .= $pixels[$i2++];
	}
    }


    // calculate a Adler32 checksum with the bytes data[start..len-1]
    $s1 = 1;
    $s2 = 0;
    for ($n = $start; $n < strlen($data); $n++) {
	$s1 = ($s1 + ord($data[$n])) % 65521;
	$s2 = ($s2 + $s1) % 65521;
    }
    $adler = ($s2 << 16) | $s1;

    $data .= chr(($adler >> 24) & 255);
    $data .= chr(($adler >> 16) & 255);
    $data .= chr(($adler >> 8) & 255);
    $data .= chr($adler & 255);
    add_chunk("IDAT");

    // IEND: marks the end of the PNG-file
    $data = "";
    add_chunk("IEND");

    // print the image
    header("Content-type: image/png");
    print($result);
?>