使用php GD库将透明渐变与图像混合 [英] Blend transparent gradient with an image using php GD library
问题描述
我尝试在图像上渲染渐变,它需要从全彩色到透明,这是我的代码。我得到黑色图像,如果我把开始更多然后0我得到白色渐变但没有图像。输出图像为338x100像素,但如果图像较窄,则输入图像需要右对齐。
I try to render gradient on top of an image it need to be from full color to transparent, here is my code. I get black image and if I put start more then 0 I got white gradient but no image. the output image is 338x100 px but the input image need to be aligned to right if the image is narrower.
function hex2rgb($hex) {
$rgb[0] = hexdec(substr($hex, 0, 2));
$rgb[1] = hexdec(substr($hex, 2, 2));
$rgb[2] = hexdec(substr($hex, 4, 2));
return $rgb;
}
function int2rgb($color) {
$result[] = ($color >> 16) & 0xFF;
$result[] = ($color >> 8) & 0xFF;
$result[] = $color & 0xFF;
return $result;
}
if (isset($_GET['start']) && isset($_GET['stop']) && isset($_GET['color'])) {
$input = imagecreatefrompng('file.png');
$width = imagesx($input);
$output = imagecreatetruecolor(338, 100);
$color = hex2rgb($_GET['color']);
$fill = imagecolorallocate($output, $color[0], $color[1], $color[2]);
for ($x=0; $x<$_GET['start']; ++$x) {
for ($y=0; $y<100; ++$y) {
imagesetpixel($output, $x, $y, $fill);
}
}
$range = $_GET['stop']-$_GET['start'];
for ($x=$_GET['start']; $x<$_GET['stop']; ++$x) {
$alpha = round(255-($x*255/$range));
$correct_x = $width < 338 ? $x+$width-338 : $x;
for ($y=0; $y<100; ++$y) {
$input_color = int2rgb(imagecolorat($input, $correct_x, $y));
$new_color = imagecolorallocate($output,
(($color[0]-$alpha)*$input_color[0])/255,
(($color[1]-$alpha)*$input_color[1])/255,
(($color[2]-$alpha)*$input_color[2])/255);
imagesetpixel($output, $x, $y, $new_color);
}
}
if ($_GET['stop']<338) {
$stop = $width < 338 ? $_GET['stop']+$width-338 : $_GET['stop'];
imagecopy($input, $output, $stop, 0, $_GET['stop'], 0, 338-$stop, 100);
header('Content-Type: image/png');
imagepng($output);
}
}
我用运行脚本gradient.php?start = 20& stop = 200& color = ff0000
并得到此而不是红色渐变。
I run the script with gradient.php?start=20&stop=200&color=ff0000
and got this instead of red gradient.
如何将渐变红色从全彩色变为完全透明?所以它看起来像这样:
How to make that gradient red from full color to full transparent? So it look like this:
推荐答案
如果使用 imagecreatetruecolor 它获得黑色背景。使用 imagefill ,您可以轻松更改图像的背景。使用 imagecolorallocatealpha 功能,您可以创建包含透明度的颜色。 127表示完全透明,0表示不透明。
If you create a image using imagecreatetruecolor it gets a black background. Using imagefill you can change the background of an image easily. The imagecolorallocatealpha function let's you create a color containing transparency. 127 means fully transparent and 0 not transparent.
现在可以使用,我简化了你的代码:
It works now and I simplified your code a bit:
function hex2rgb($hex) {
$rgb[0] = hexdec(substr($hex, 0, 2));
$rgb[1] = hexdec(substr($hex, 2, 2));
$rgb[2] = hexdec(substr($hex, 4, 2));
return $rgb;
}
if (isset($_GET['start']) && isset($_GET['stop']) && isset($_GET['color'])) {
$color = hex2rgb($_GET['color']);
$range = $_GET['stop']-$_GET['start'];
// create input image
$input = imagecreatefrompng('file.png');
// create output image
$height = imagesy($input);
$width = imagesx($input);
$output = imagecreatetruecolor($width, $height);
// put a transparent background on it
$trans_colour = imagecolorallocatealpha($output, 0, 0, 0, 127);
imagefill($output, 0, 0, $trans_colour);
// create the gradient
for ($x=0; $x < $width; ++$x) {
$alpha = $x <= $_GET['start'] ? 0 : round(min(($x - $_GET['start'])/$range, 1)*127);
$new_color = imagecolorallocatealpha($output, $color[0], $color[1], $color[2], $alpha);
imageline($output, $x, $height, $x, 0, $new_color);
}
// copy the gradient onto the input image
imagecopyresampled($input, $output, 0, 0, 0, 0, $width, $height, $width, $height);
// output the result
header('Content-Type: image/png');
imagepng($input);
}
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