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1 /** | |
2 * A handy class to calculate color values. | |
3 * | |
4 * @version 1.0 | |
5 * @author Robert Eisele <robert@xarg.org> | |
6 * @copyright Copyright (c) 2010, Robert Eisele | |
7 * @link http://www.xarg.org/2010/03/generate-client-side-png-files-using-javascr
ipt/ | |
8 * @license http://www.opensource.org/licenses/bsd-license.php BSD License | |
9 * | |
10 */ | |
11 | |
12 (function() { | |
13 | |
14 // helper functions for that ctx | |
15 function write(buffer, offs) { | |
16 for (var i = 2; i < arguments.length; i++) { | |
17 for (var j = 0; j < arguments[i].length; j++) { | |
18 buffer[offs++] = arguments[i].charAt(j); | |
19 } | |
20 } | |
21 } | |
22 | |
23 function byte2(w) { | |
24 return String.fromCharCode((w >> 8) & 255, w & 255); | |
25 } | |
26 | |
27 function byte4(w) { | |
28 return String.fromCharCode((w >> 24) & 255, (w >> 16) & 255, (w >> 8) &
255, w & 255); | |
29 } | |
30 | |
31 function byte2lsb(w) { | |
32 return String.fromCharCode(w & 255, (w >> 8) & 255); | |
33 } | |
34 | |
35 window.PNGlib = function(width,height,depth) { | |
36 | |
37 this.width = width; | |
38 this.height = height; | |
39 this.depth = depth; | |
40 | |
41 // pixel data and row filter identifier size | |
42 this.pix_size = height * (width + 1); | |
43 | |
44 // deflate header, pix_size, block headers, adler32 checksum | |
45 this.data_size = 2 + this.pix_size + 5 * Math.floor((0xfffe + this.pix_s
ize) / 0xffff) + 4; | |
46 | |
47 // offsets and sizes of Png chunks | |
48 this.ihdr_offs = 0; // IHDR offset an
d size | |
49 this.ihdr_size = 4 + 4 + 13 + 4; | |
50 this.plte_offs = this.ihdr_offs + this.ihdr_size; // PLTE offset and
size | |
51 this.plte_size = 4 + 4 + 3 * depth + 4; | |
52 this.trns_offs = this.plte_offs + this.plte_size; // tRNS offset and
size | |
53 this.trns_size = 4 + 4 + depth + 4; | |
54 this.idat_offs = this.trns_offs + this.trns_size; // IDAT offset and
size | |
55 this.idat_size = 4 + 4 + this.data_size + 4; | |
56 this.iend_offs = this.idat_offs + this.idat_size; // IEND offset and
size | |
57 this.iend_size = 4 + 4 + 4; | |
58 this.buffer_size = this.iend_offs + this.iend_size; // total PNG siz
e | |
59 | |
60 this.buffer = new Array(); | |
61 this.palette = new Object(); | |
62 this.pindex = 0; | |
63 | |
64 var _crc32 = new Array(); | |
65 | |
66 // initialize buffer with zero bytes | |
67 for (var i = 0; i < this.buffer_size; i++) { | |
68 this.buffer[i] = "\x00"; | |
69 } | |
70 | |
71 // initialize non-zero elements | |
72 write(this.buffer, this.ihdr_offs, byte4(this.ihdr_size - 12), 'IHDR', b
yte4(width), byte4(height), "\x08\x03"); | |
73 write(this.buffer, this.plte_offs, byte4(this.plte_size - 12), 'PLTE'); | |
74 write(this.buffer, this.trns_offs, byte4(this.trns_size - 12), 'tRNS'); | |
75 write(this.buffer, this.idat_offs, byte4(this.idat_size - 12), 'IDAT'); | |
76 write(this.buffer, this.iend_offs, byte4(this.iend_size - 12), 'IEND'); | |
77 | |
78 // initialize deflate header | |
79 var header = ((8 + (7 << 4)) << 8) | (3 << 6); | |
80 header+= 31 - (header % 31); | |
81 | |
82 write(this.buffer, this.idat_offs + 8, byte2(header)); | |
83 | |
84 // initialize deflate block headers | |
85 for (var i = 0; (i << 16) - 1 < this.pix_size; i++) { | |
86 var size, bits; | |
87 if (i + 0xffff < this.pix_size) { | |
88 size = 0xffff; | |
89 bits = "\x00"; | |
90 } else { | |
91 size = this.pix_size - (i << 16) - i; | |
92 bits = "\x01"; | |
93 } | |
94 write(this.buffer, this.idat_offs + 8 + 2 + (i << 16) + (i << 2), bi
ts, byte2lsb(size), byte2lsb(~size)); | |
95 } | |
96 | |
97 /* Create crc32 lookup table */ | |
98 for (var i = 0; i < 256; i++) { | |
99 var c = i; | |
100 for (var j = 0; j < 8; j++) { | |
101 if (c & 1) { | |
102 c = -306674912 ^ ((c >> 1) & 0x7fffffff); | |
103 } else { | |
104 c = (c >> 1) & 0x7fffffff; | |
105 } | |
106 } | |
107 _crc32[i] = c; | |
108 } | |
109 | |
110 // compute the index into a png for a given pixel | |
111 this.index = function(x,y) { | |
112 var i = y * (this.width + 1) + x + 1; | |
113 var j = this.idat_offs + 8 + 2 + 5 * Math.floor((i / 0xffff) + 1) +
i; | |
114 return j; | |
115 } | |
116 | |
117 // convert a color and build up the palette | |
118 this.color = function(red, green, blue, alpha) { | |
119 | |
120 alpha = alpha >= 0 ? alpha : 255; | |
121 var color = (((((alpha << 8) | red) << 8) | green) << 8) | blue; | |
122 | |
123 if (typeof this.palette[color] == "undefined") { | |
124 if (this.pindex == this.depth) return "\x00"; | |
125 | |
126 var ndx = this.plte_offs + 8 + 3 * this.pindex; | |
127 | |
128 this.buffer[ndx + 0] = String.fromCharCode(red); | |
129 this.buffer[ndx + 1] = String.fromCharCode(green); | |
130 this.buffer[ndx + 2] = String.fromCharCode(blue); | |
131 this.buffer[this.trns_offs+8+this.pindex] = String.fromCharCode(
alpha); | |
132 | |
133 this.palette[color] = String.fromCharCode(this.pindex++); | |
134 } | |
135 return this.palette[color]; | |
136 } | |
137 | |
138 // output a PNG string, Base64 encoded | |
139 this.getBase64 = function() { | |
140 | |
141 var s = this.getDump(); | |
142 | |
143 var ch = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz012345
6789+/="; | |
144 var c1, c2, c3, e1, e2, e3, e4; | |
145 var l = s.length; | |
146 var i = 0; | |
147 var r = ""; | |
148 | |
149 do { | |
150 c1 = s.charCodeAt(i); | |
151 e1 = c1 >> 2; | |
152 c2 = s.charCodeAt(i+1); | |
153 e2 = ((c1 & 3) << 4) | (c2 >> 4); | |
154 c3 = s.charCodeAt(i+2); | |
155 if (l < i+2) { e3 = 64; } else { e3 = ((c2 & 0xf) << 2) | (c3 >>
6); } | |
156 if (l < i+3) { e4 = 64; } else { e4 = c3 & 0x3f; } | |
157 r+= ch.charAt(e1) + ch.charAt(e2) + ch.charAt(e3) + ch.charAt(e4
); | |
158 } while ((i+= 3) < l); | |
159 return r; | |
160 } | |
161 | |
162 // output a PNG string | |
163 this.getDump = function() { | |
164 | |
165 // compute adler32 of output pixels + row filter bytes | |
166 var BASE = 65521; /* largest prime smaller than 65536 */ | |
167 var NMAX = 5552; /* NMAX is the largest n such that 255n(n+1)/2 + (
n+1)(BASE-1) <= 2^32-1 */ | |
168 var s1 = 1; | |
169 var s2 = 0; | |
170 var n = NMAX; | |
171 | |
172 for (var y = 0; y < this.height; y++) { | |
173 for (var x = -1; x < this.width; x++) { | |
174 s1+= this.buffer[this.index(x, y)].charCodeAt(0); | |
175 s2+= s1; | |
176 if ((n-= 1) == 0) { | |
177 s1%= BASE; | |
178 s2%= BASE; | |
179 n = NMAX; | |
180 } | |
181 } | |
182 } | |
183 s1%= BASE; | |
184 s2%= BASE; | |
185 write(this.buffer, this.idat_offs + this.idat_size - 8, byte4((s2 <<
16) | s1)); | |
186 | |
187 // compute crc32 of the PNG chunks | |
188 function crc32(png, offs, size) { | |
189 var crc = -1; | |
190 for (var i = 4; i < size-4; i += 1) { | |
191 crc = _crc32[(crc ^ png[offs+i].charCodeAt(0)) & 0xff] ^ ((c
rc >> 8) & 0x00ffffff); | |
192 } | |
193 write(png, offs+size-4, byte4(crc ^ -1)); | |
194 } | |
195 | |
196 crc32(this.buffer, this.ihdr_offs, this.ihdr_size); | |
197 crc32(this.buffer, this.plte_offs, this.plte_size); | |
198 crc32(this.buffer, this.trns_offs, this.trns_size); | |
199 crc32(this.buffer, this.idat_offs, this.idat_size); | |
200 crc32(this.buffer, this.iend_offs, this.iend_size); | |
201 | |
202 // convert PNG to string | |
203 return "\211PNG\r\n\032\n"+this.buffer.join(''); | |
204 } | |
205 } | |
206 | |
207 })(); | |
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