duanlu7680 2013-02-04 10:18
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使用php GD库将透明渐变与图像混合

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);
    }
}

I run the script with gradient.php?start=20&stop=200&color=ff0000 and got this instead of red gradient.

enter image description hereenter image description here

How to make that gradient red from full color to full transparent? So it look like this:

enter image description here

  • 写回答

1条回答 默认 最新

  • doudou1897 2013-02-08 15:18
    关注

    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.

    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);
    }
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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