michael@0: function makePattern(len, start, inc) {
michael@0:   var pattern = [];
michael@0:   while(len) {
michael@0:     pattern.push(start);
michael@0:     start = (start + inc) % 256;
michael@0:     --len;
michael@0:   }
michael@0:   return pattern;
michael@0: }
michael@0: 
michael@0: function setPattern(imageData, pattern) {
michael@0:   if (pattern.length != imageData.data.length)
michael@0:     throw Error('Invalid pattern');
michael@0:   for (var i = 0; i < pattern.length; ++i)
michael@0:     imageData.data[i] = pattern[i];
michael@0: }
michael@0: 
michael@0: function checkPattern(imageData, pattern) {
michael@0:   if (pattern.length != imageData.data.length)
michael@0:     throw Error('Invalid pattern');
michael@0:   for (var i = 0; i < pattern.length; ++i)
michael@0:     if (imageData.data[i] != pattern[i])
michael@0:       return false;
michael@0:   return true;
michael@0: }