phpImageWorkshop: Removing a layer after saving - php

Question

In the phpImageWorkshop documentation (http://phpimageworkshop.com/doc/13/saving.html) it says:
...after saving, you'll be able to continue to use your document and
to perform some actions on its sublayers, really convenient !
However, after calling save() I'm unable to remove the watermark layer.
I start by loading the photo and watermark and resize the photo:
$photo = PHPImageWorkshop\ImageWorkshop::initFromPath($tmp_name);
$mark = PHPImageWorkshop\ImageWorkshop::initFromPath($watermark);
$photo->resizeInPixel(960, null, true);
And then I add the watermark, save the photo, then remove the watermark (so I can make other sizes without a watermark without creating a new object):
$photo->addLayer(1, $mark, 0, 0, 'LB');
$photo->save($path, $filename, false, null, 80); // file correctly has watermark
$photo->remove(1);
$photo->resizeInPixel(550, null, true);
$photo->save($path, $filename, false, null, 80); // file has watermark, not correct
This does not delete the watermark layer. However, if I call remove() before save() it will remove the watermark:
$photo->addLayer(1, $mark, 0, 0, 'LB');
$photo->remove(1); // calling remove() before save removes watermark
$photo->save($path, $filename, false, null, 80); // file does not have watermark
I cannot understand why this is happening, since the documentation clearly says calling save() does not change the layers.
I've confirmed that the watermark layer is being put on layer level 1, and it works OK if I do not call save().

Answer 1

Despite the documentation saying you'll be able to continue to use your document, the fact is that the save() function calls getResult() which returns a merged resource image (this is in ImageWorkshopLayer.php)
However, if you create a 'base layer' and add the photo and watermark on top of it, the save() function appears to merge to the base layer - leaving the photo and mark untouched, so you can remove the mark and re-save (which causes the photo to be re-merged onto the base layer) i.e.
$baseimg = PHPImageWorkshop\ImageWorkshop::initVirginLayer(1024,800);
$photo = PHPImageWorkshop\ImageWorkshop::initFromPath("test.png");
$mark = PHPImageWorkshop\ImageWorkshop::initFromPath("test2.png");
$iphoto= $baseimg->addLayerOnTop($photo, 0, 0, 'LB');
$imark= $baseimg->addLayerOnTop($mark, 0, 0, 'LB');
$baseimg->resizeInPixel(960, null, true);
// file correctly has watermark
$baseimg->save(__DIR__, "test_out.png", false, null, 80);
$baseimg->remove($imark['id']);
// file correctly has no watermark
$baseimg->save(__DIR__, "test_out2.png", false, null, 80);
Note that I use the return value from addLayerOnTop() to determine the 'id' pf the layer to remove.
EDIT: although the above works, it is not ideal because you really need the resulting image to be the size of the re-sized photo. Also I found that once the photo is made a layer, you have to resize that layer (not the original photo) so...
// load photo and mark
$photo = PHPImageWorkshop\ImageWorkshop::initFromPath("test.png");
$mark = PHPImageWorkshop\ImageWorkshop::initFromPath("test2.png");
// resize the photo 1st time
$photo->resizeInPixel(960,null, true);
$width= $photo->getWidth();
$height= $photo->getHeight();
// make empty base image same size as photo
$baseimg = PHPImageWorkshop\ImageWorkshop::initVirginLayer($width,$height);
// add photo and mark onto base image
$iphoto= $baseimg->addLayerOnTop($photo, 0, 0, 'LT');
$imark= $baseimg->addLayerOnTop($mark, 0, 0, 'LT');
$photoid= $iphoto['id']; // get layer id's
$markid= $imark['id'];
// file correctly has watermark
$baseimg->save(__DIR__, "test_out.png", false, null, 80);
// remove mark layer
$baseimg->remove($imark['id']);
// resize photo again
// - photo is now a layer in baseimg
$baseimg->layers[$photoid]->resizeInPixel(550,null, true);
$width= $baseimg->layers[$photoid]->getWidth();
$height= $baseimg->layers[$photoid]->getHeight();
// crop baseimg to match photo size
$baseimg->cropInPixel($width,$height);
// file correctly has no watermark
$baseimg->save(__DIR__, "test_out2.png", false, null, 80);
That seems to work fine now.