满屏水印代码调用：

// 增加水印
function addImageWater($sourcePath,$logoPath,$savePath){
    $im = imagecreatefromstring(file_get_contents($sourcePath));
    //获取水印源
    $watermark = imagecreatefromstring(file_get_contents($logoPath));
    //获取图、水印 宽高类型
    list($bgWidth, $bgHight, $bgType) = getimagesize($sourcePath);
    list($logoWidth, $logoHight, $logoType) = getimagesize($logoPath);
    //定义平铺数据
    $x_length = $bgWidth - 10; //x轴总长度
    $y_length = $bgHight - 10; //y轴总长度
    //创建透明画布 伪白色
    $opacity=20;
    $w = imagesx($watermark);
    $h = imagesy($watermark);
    $cut = imagecreatetruecolor($w,$h);
    $white = imagecolorallocatealpha($cut, 255,255,255,0);
    imagefill( $cut, 0, 0, $white );
    //整合水印