Call new pre_scale and get_or_generate from plone.scale.

.gitignore

@@ -11,3 +11,4 @@ include
 lib
 parts
 requirements-*-mxdev.txt
+sources/

news/113.feature.1

@@ -0,0 +1,2 @@
+Creating a tag no longer generates the actual scale.
+[maurits]

news/113.feature.2

@@ -0,0 +1,5 @@
+Add ``@@images-test`` page for Editors.
+This shows various variants from the image field of the current context.
+It shows a list of stored scales.
+It allows purging the stored scales.
+[maurits]

news/113.feature.3

@@ -0,0 +1,5 @@
+Add picture method to to ImageScaling and include it in @@image-test.
+Picture tags only work on Plone 6, with several other branches for picture variants merged.
+See `plip-image-srcsets.cfg <https://github.com/plone/buildout.coredev/blob/6.0/plips/plip-image-srcsets.cfg>`_.
+If not available (like on Plone 5.2), an ordinary image tag is created.
+[MrTango]

plone/namedfile/picture.py

@@ -0,0 +1,143 @@
+import logging
+import re
+
+from plone.namedfile.interfaces import IAvailableSizes
+from plone.app.uuid.utils import uuidToObject
+from plone.registry.interfaces import IRegistry
+from zope.component import getUtility
+from zope.component import queryUtility
+from bs4 import BeautifulSoup
+
+try:
+    from plone.base.interfaces import IImagingSchema
+except ImportError:
+    from Products.CMFPlone.interfaces.controlpanel import IImagingSchema
+
+
+logger = logging.getLogger("plone.outputfilter.picture_variant")
+appendix_re = re.compile("^(.*)([?#].*)$")
+resolveuid_re = re.compile("^[./]*resolve[Uu]id/([^/]*)/?(.*)$")
+
+
+def get_allowed_scales():
+    sizes_util = queryUtility(IAvailableSizes)
+    if sizes_util is None:
+        return {}
+    sizes = sizes_util()
+    if sizes is None:
+        return {}
+    return sizes
+
+
+def get_picture_variants():
+    registry = getUtility(IRegistry)
+    settings = registry.forInterface(IImagingSchema, prefix="plone", check=False)
+    return getattr(settings, "picture_variants", {})
+
+
+class Img2PictureTag(object):
+    def get_scale_name(self, scale_line):
+        parts = scale_line.split(" ")
+        return parts and parts[0] or ""
+
+    def get_scale_width(self, scale):
+        """get width from allowed_scales line
+        large 800:65536
+        """
+        allowed_scales = get_allowed_scales()
+        scale_info = allowed_scales.get(scale)
+        return scale_info[0]
+
+    def create_picture_tag(
+        self, sourceset, attributes, uid=None, fieldname=None, resolve_urls=False
+    ):
+        """Converts the img tag to a picture tag with picture_variant definition"""
+        width = None
+        height = None
+        src = attributes.get("src")
+        if not uid and not src:
+            raise TypeError("Either uid or attributes['src'] need to be given.")
+        soup = BeautifulSoup("", "html.parser")
+        allowed_scales = get_allowed_scales()
+        if uid:
+            obj = uuidToObject(uid)
+        else:
+            obj = self.resolve_uid_url(src)
+        picture_tag = soup.new_tag("picture")
+        css_classes = attributes.get("class", [])
+        if "captioned" in css_classes:
+            picture_tag["class"] = "captioned"
+        for i, source in enumerate(sourceset):
+            target_scale = source["scale"]
+            media = source.get("media")
+
+            additional_scales = source.get("additionalScales", None)
+            if additional_scales is None:
+                additional_scales = [
+                    self.get_scale_name(s) for s in allowed_scales if s != target_scale
+                ]
+            source_scales = [target_scale] + additional_scales
+            source_srcset = []
+            for scale in source_scales:
+                if resolve_urls and obj:
+                    scale_view = obj.unrestrictedTraverse("@@images", None)
+                    scale_obj = scale_view.scale(fieldname, scale, pre=True)
+                    scale_url = scale_obj.url
+                else:
+                    # obj = self.resolve_uid_url(src)
+                    # scale_view = obj.unrestrictedTraverse("@@images", None)
+                    # scale_obj = scale_view.scale(fieldname, scale, pre=True)
+                    # scale_url = scale_obj.url
+                    scale_url = self.update_src_scale(src=src, scale=scale)
+                scale_width = self.get_scale_width(scale)
+                source_srcset.append("{0} {1}w".format(scale_url, scale_width))
+            source_tag = soup.new_tag("source", srcset=",\n".join(source_srcset))
+            if media:
+                source_tag["media"] = media
+            picture_tag.append(source_tag)
+            if i == len(sourceset) - 1:
+                if resolve_urls and obj:
+                    scale_view = obj.unrestrictedTraverse("@@images", None)
+                    scale_obj = scale_view.scale(fieldname, target_scale, pre=True)
+                    scale_url = scale_obj.url
+                    width = scale_obj.width
+                    height = scale_obj.height
+                else:
+                    # obj = self.resolve_uid_url(src)
+                    # scale_view = obj.unrestrictedTraverse("@@images", None)
+                    # scale_obj = scale_view.scale(fieldname, target_scale, pre=True)
+                    # scale_url = scale_obj.url
+                    # width = scale_obj.width
+                    # height = scale_obj.height
+                    scale_url = self.update_src_scale(src=src, scale=target_scale)
+                img_tag = soup.new_tag("img", src=scale_url)
+                for k, attr in attributes.items():
+                    if k in ["src", "srcset"]:
+                        continue
+                    img_tag.attrs[k] = attr
+                img_tag["loading"] = "lazy"
+                if width:
+                    img_tag["width"] = width
+                if height:
+                    img_tag["height"] = height
+                picture_tag.append(img_tag)
+        return picture_tag
+
+    def resolve_uid_url(self, href):
+        obj = None
+        subpath = href
+        match = resolveuid_re.match(subpath)
+        if match is not None:
+            uid, _subpath = match.groups()
+            obj = uuidToObject(uid)
+        return obj
+
+    def update_src_scale(self, src, scale):
+        parts = src.split("/")
+        if "." in parts[-1]:
+            field_name = parts[-1].split("-")[0]
+            src_scale = "/".join(parts[:-1]) + "/{0}/{1}".format(field_name, scale)
+            src_scale
+        else:
+            src_scale = "/".join(parts[:-1]) + "/{}".format(scale)
+        return src_scale