Images in page templates

Description

How to link to images in page templates in Plone.

Putting a static image into a page template

Here is an example how to create an <img> tag in a .pt file:

<img tal:attributes="src string:${context/@@plone_portal_state/portal_url}/++resource++plonetheme.mfabrik/close-icon.png" alt="[ X ]"/>

Let’s break this down:

  • We are rendering an <img> tag.
  • The src attribute is dynamically generated using a TALES expression.
  • We use string comprehension to create the src attribute. Alternatively we could use e.g. the python: TALES expression type and embed one line python of code to generate the attribute value.
  • We look up a helper view called plone_portal_state. This is a BrowserView shipped with Plone. Its purpose is to expose different helper methods to page templates and Python code.
  • We call plone_portal_state’s portal_url() method. This will return the root URL of our site. Note that this is not necessary the domain’s top-level URL, as Plone sites can be nested in folders, or served on a path among unrelated web properties.
  • We append our Zope 3 resource path to our site root URL (see below). This maps to some static media folder in our add-on files on the disk.
  • There we point to close-icon.png image file.
  • We also add the alt attribute of the <img> tag normally. It is not dynamically generated.

When the page template is generated, the following snippet could look like, for example:

<img src="http://localhost:8080/mfabrik/++resource++plonetheme.mfabrik/logo.png" alt="[ X ]">

… or:

<img src="http://mfabrik.com/++resource++plonetheme.mfabrik/logo.png" alt="[ X ]">

… depending on the site virtual hosting configuration.

Relative image look-ups

Warning

Never create relative image look-ups without prefixing the image source URL with the site root.

Hardcoded relative image path might seem to work:

<img src="++resource++plonetheme.mfabrik/logo.png" >

… but this causes a different image base URL to be used on every page. The image URLs, from the browser point of view, would be:

<img src="http://yoursite/++resource++plonetheme.mfabrik/logo.png" >

… and then in another folder:

<img src="http://yoursite/folder/++resource++plonetheme.mfabrik/logo.png" >

… which prevents the browser from caching the image.

Registering static media folders in your add-on product

Zope 3 resource directory

The right way to put in a static image is to use a Zope 3 resource directory.

  • Create folder yourcompany.product/yourcompany/product/browser/static.
  • Add the following ZCML to yourcompany.product/yourcompany/product/browser/configure.zcml.
<browser:resourceDirectory
    name="yourcompany.product"
    directory="static"
    layer=".interfaces.IThemeSpecific"
    />

This will be picked up at the ++resource++yourcompany.product/ static media path.

Layer is optional: the static media path is available only when your add-on product is installed if the layer is specified.

Also see Resource folders

Rendering Image content items

You can refer to ATImage object’s content data download by adding /image to the URL:

<img alt="" tal:attributes="src string:${context/getImage/absolute_url}/image" />

The magic is done in the __bobo_traverse__ method of ATImage by providing traversable hooks to access image download:

Rendering ImageField

Archetypes’s ImageField maps its data to the content object at attribute which is the field’s name. If you have a field campaignVideoThumbnail you can generate an image tag as follows:

<img class="thumbnail" tal:attributes="src string:${campaign/absolute_url}/campaignVideoThumbnail" alt="Campaign video" />

If you need more complex <img> output, create a helper function in your BrowserView and use Python code to perform the ImageField manipulation.

See ImageField for more information:

tag() method

Note

Using tag() is discouraged. Create your image tags manually.

Some content provides a handy tag() method to generate <img src="" /> tags with different image sizes.

tag() is available on

  • Archetypes ImageField
  • ATNewsItem
  • ATImage
  • FSImage (Zope 2 image object on the file-system)

tag() is defined in OFS.Image.

Scaling images

tag() supports scaling. Scale sizes are predefined. When an ATImage is uploaded, various scaled versions of it are stored in the database.

Displaying a version of the image using the “preview” scale:

image.tag(scale="preview", alt="foobar text")

This will generate:

<img src="http://something/folder/image/image_preview" alt="foobar text" />

Note

If you are not using the alt attribute, you should set it to an empty string: alt="". Otherwise screen readers will read the src attribute of the <img> tag aloud.

In order to simplify accessing these image scales, use archetypes.fieldtraverser. This package allows you to traverse to the stored image scales while still using AnnotationStorage and is a lot simpler to get going (in the author’s humble opinion :).

Default scale names and sizes are defined in ImageField declaration for custom ImageFields. For ATImage, those are in Products.ATContentTypes.content.image.