scale uploaded image from canvas on webserver with php

Question

my issue is to upload the current canvas not only as a JSON Object in my Database, I also want to save a thumbnail from the canvas. It is for a kind of layout gallery.

Nearly everything is working except the scale to e specific size. I used this Tutorial for the PHP function function scaleImg(); Scale Image with PHP

So here is my Code from the upload script:

layoutupload.php

...
    //Save canvas as thumbnail


 //datafields
     $lt_dir = "../flyer/templateDATA/template_1_thumbs/";
     $lt_canvas_thumb = $_POST['lt_canvas_thumb'];

     //delete header
     $lt_canvas_thumb = str_replace('data:image/png;base64,','', $lt_canvas_thumb);
     $lt_canvas_thumb = str_replace(' ', '+', $lt_canvas_thumb);

     //decode to an image
     $img_data = base64_decode($lt_canvas_thumb);
     $file = $lt_dir.'tmp.png';

     //save in filesystem
     $success = file_put_contents($file, $img_data);
     print $success ? $file : 'Unable to save the file.';

     //scale img with helper class
     include "helper_scaleImg.php";
     scaleImg($file,100,141,'png'); // ($img,$width,$height,$type)
...

This var lt_canvas_thumb = canvas.toDataURL("image/png"); comes from a JavaScript function
I can save the image on the filesystem but only with the original canvas dimensions (370x522).

Here is the PHP script for scaling

function scaleImg($img, $width, $height, $type){

//$type = exif_imagetype($img);
//Possible types
//IMAGETYPE_JPEG
//IMAGETYPE_PNG

if($type == 'jpg'){

    $source_image = imagecreatefromjpeg($img);

    // Get the size of img
    $source_imagex = imagesx($source_image); //width
    $source_imagey = imagesy($source_image); //height

    // destination image
    $dest_imagex = $width;
    $dest_imagey = $height;
    $dest_image = imagecreatetruecolor($dest_imagex, $dest_imagey);

    //best quality (slow)
    imagecopyresampled($dest_image, $source_image, 0, 0, 0, 0, 
            $dest_imagex, $dest_imagey, $source_imagex, $source_imagey);

    return imagejpeg($dest_image,NULL,100);


}
else if($type == 'png'){

    $source_image = imagecreatefrompng($img);

    if(!$source_image){
        // Get the size of img
        $source_imagex = imagesx($source_image); //width
        $source_imagey = imagesy($source_image); //height

        // destination image
        $dest_imagex = $width;
        $dest_imagey = $height;
        $dest_image = imagecreatetruecolor($dest_imagex, $dest_imagey);

        //best quality (slow)
        imagecopyresampled($dest_image, $source_image, 0, 0, 0, 0, 
                $dest_imagex, $dest_imagey, $source_imagex, $source_imagey);

        /* Output an error message */
        imagestring($source_image, 1, 5, 5, 'Error loading ' . $img);
    }

    return imagepng($dest_image,NULL,9);
    //return $dest_image;
}
else
{
    echo "Invalid image type!";
    exit;
}

}

I'm getting the following error message:

Data: ../flyer/templateDATA/template_1_thumbs/tmp.png
Warning: imagepng() expects parameter 1 to be resource, null given in /Applications/XAMPP/xamppfiles/htdocs/flyer/helper_scaleImg.php on line 57

I don't know why it's "null", because the File is correctly saved in my directory.
I hope it issn't a small mistake in my code, and I hope someone can help me. Thanks! Greetings Max

Answer 1

if(!$source_image) is evaluating to false if the source image loads, and so the block of code that defines $dest_image is being skipped.