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Generate <img> markup block for an image.

Project description

canonicalwebteam.image\_template
================================

A module to generate performant HTML image markup for images hosted on
``assets.ubuntu.com``. The markup will:

- Use ``data-src`` attributes for
`lazysizes <https://github.com/aFarkas/lazysizes>`__
- Use predefined ``srcset`` break points
- Resize the image with ``?w=XX&h=XX`` query parameters
- Prefix all image URLs with cloudinary proxy URLs, for CDN and image
transformations

Parameters
----------

- ``path`` (mandatory string): The path to an asset on
assets.ubuntu.com (e.g. ``/v1/9f6916dd-k8s-prometheus-light.png``)
- ``alt`` (mandatory string): Alt text to describe the image
- ``width`` (mandatory integer): The number of pixels wide the image
should be
- ``height`` (mandatory integer): The number of pixels high the image
should be
- ``col`` (optional): The number of Vanilla columns the image should
span (helps define break points efficiently)

Usage
-----

The `image_template` function can be used directly to generate image Markup.

```
from canonicalwebteam import image_template

image_markup = image_template(
path="/v1/9f6916dd-k8s-prometheus-light.png",
alt="Operational dashboard",
width="1040",
height="585"
)
```

However, the most common usage is to add it to Django or Flask template contexts, as an `image` function.

Add lazysizes
~~~~~~~~~~~~~

The markup generated will use [lazysizes](https://github.com/aFarkas/lazysizes) format - it will use `data-src` instead of `src` and add the `lazyload` class.

Therefore to use this plugin you need to have lazysizes loaded on your pages. The simplest way to achieve this is to include this in your `<head>`:

.. code:: html

<script src="https://assets.ubuntu.com/v1/842d27d3-lazysizes.min.js" async=""></script>

Django usage
~~~~~~~~~~~~

Add it as a template tag:

.. code:: python3

# myapp/templatetags.py

from canonicalwebteam import image_template
from django import template
from django.utils.safestring import mark_safe


register = template.Library()

@register.simple_tag
def image(*args, **kwargs):
return mark_safe(image_template(*args, **kwargs))


# settings.py

TEMPLATES[0]["OPTIONS"]["builtins"].append("myapp.templatetags")

Use it in templates:

.. code:: html

# templates/mytemplate.html

{% image path="/v1/9f6916dd-k8s-prometheus-light.png" alt="Operational dashboard" width="1040" height="585" %}

Flask usage
~~~~~~~~~~~

Add it as a template tag:

.. code:: python3

# app.py

from canonicalwebteam import image_template
from flask import Flask

app = Flask(__name__)

@app.context_processor
def utility_processor():
return {"image": image_template}

Use it in templates:

.. code:: html

# templates/mytemplate.html

{{
image(
path="/v1/9f6916dd-k8s-prometheus-light.png",
alt="Operational dashboard",
width="1040",
height="585"
) | safe
}}

Generated markup
~~~~~~~~~~~~~~~~

All the above examples will generate the following markup:

.. code:: html

<img
data-srcset="https://res.cloudinary.com/canonical/image/fetch/q_auto,f_auto,w_412/https://assets.ubuntu.com/v1/9f6916dd-k8s-prometheus-light.png?w=1040&h=585 460w
,https://res.cloudinary.com/canonical/image/fetch/q_auto,f_auto,w_572/https://assets.ubuntu.com/v1/9f6916dd-k8s-prometheus-light.png?w=1040&h=585 620w
,https://res.cloudinary.com/canonical/image/fetch/q_auto,f_auto,w_720/https://assets.ubuntu.com/v1/9f6916dd-k8s-prometheus-light.png?w=1040&h=585 767w
,https://res.cloudinary.com/canonical/image/fetch/q_auto,f_auto,w_990/https://assets.ubuntu.com/v1/9f6916dd-k8s-prometheus-light.png?w=1040&h=585 1030w"
data-src="https://res.cloudinary.com/canonical/image/fetch/q_auto,f_auto/https://assets.ubuntu.com/v1/9f6916dd-k8s-prometheus-light.png?w=1040&h=585"
sizes="100vw"
alt="test"
width="1040"
height="585"
class="lazyload"
/>

<noscript>
<img
src="https://res.cloudinary.com/canonical/image/fetch/q_auto,f_auto/https://assets.ubuntu.com/v1/9f6916dd-k8s-prometheus-light.png?w=1040&h=585"
alt="Operational dashboard"
width="1040"
height="585"
/>
</noscript>

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