/* 颜色渐变*/
function extract16color($color16) {
$mask16 = "0123456789ABCDEF";
$true_color = [0, 0, 0];
$color16 = mb_substr($color16, 1);
for ($i = 0; $i < 3; $i++) {
$color16_temp = [mb_substr($color16, $i * 2, 1), mb_substr($color16, $i * 2 + 1, 1)];
for ($j = 0; $j < 2; $j++) {
for ($k = 0; $k < 15; $k++) {
if ($color16_temp[$j] == $mask16[$k]) {
$color16_temp[$j] = $k;
break;
}
}
}
$true_color[$i] = intval($color16_temp[0]) * 16 + intval($color16_temp[1]);
}
return $true_color;
}
function make16color($color10) {
$mask16 = "0123456789ABCDEF";
$true_color = "#";
for ($i = 0; $i < 3; $i++) {
$color10_temp = $color10[$i];
$true_color.= $mask16[intval($color10_temp / 16)];
$true_color.= $mask16[intval($color10_temp % 16)];
}
return $true_color;
}
function str2gradient($text, $sColor, $eColor) {
$text = trim($text);
$sColor = preg_match("#^\#[a-f0-9]{6}$#i", $sColor) ? $sColor : "#000000";
$eColor = preg_match("#^\#[a-f0-9]{6}$#i", $eColor) ? $eColor : "#000000";
$color_move = [0, 0, 0];
$color_add = [0, 0, 0];
$length = mb_strlen($text);
$output = NULL;
$copy_color = NULL;
$current_color = NULL;
$max = 0;
if ($length > 0) {
$sColor = extract16color($sColor);
$eColor = extract16color($eColor);
$cColor = $sColor;
for ($i = 0; $i < 3; $i++) {
$temp = $sColor[$i] - intval($eColor[$i]);
$temp_a = abs($temp);
$color_add[$i] = $temp_a;
if ($temp_a > $max) {
$max = $temp_a;
}
if ($temp < 0) {
$color_move[$i] = 1;
} elseif ($temp > 0) {
$color_move[$i] = -1;
} else {
$color_move[$i] = 0;
}
}
for ($i = 0; $i < $length; $i++) {
$char = mb_substr($text, $i, 1);
$koeff_add = $max / $length / $max * 100;
for ($j = 0; $j < 3; $j++) {
$add = intval($color_add[$j]) / 100 * intval($koeff_add) * intval($color_move[$j]);
$cColor[$j] += $add;
}
$current_color = make16color($cColor);
if ($i == 0) {
$output.= '<font color="'.$current_color.'">'.$char;
$copy_color = $current_color;
} else {
if ($current_color == $copy_color || $char == " ") {
$output.= $char;
} else {
$output.= '</font><font color="'.$current_color.'">'.$char;
$copy_color = $current_color;
}
}
}
if (mb_strlen($output)) {
$output.= '</font>';
}
return $output;
}
}
// test
echo str2gradient('Hello, World! 你好，世界!', '#800000', '#000080');