# Renderer variables

**Any template block (aka instance of `Magento\Framework\View\Element\Template`) that has a name that starts with `loki` automatically gets certain variables inserted to make rendering other blocks or assets easier.**

These variables are:

- `$viewModelFactory` (instance of `Loki\Components\Factory\ViewModelFactory`);
- `$blockRenderer` (instance of `Loki\Components\Util\Block\BlockRenderer`);
- `$templateRenderer` (instance of `Loki\Components\Util\Block\TemplateRenderer`);
- `$childRenderer` (instance of `Loki\Components\Util\Block\ChildRenderer`);
- `$imageRenderer` (instance of `Loki\Components\Util\Block\ImageRenderer`);

The renderer variables are discussed here.

## Block rendering
The `$blockRenderer` variable - an instance of the class `\LokiCheckout\Util\Block\BlockRenderer` - allows you to render a block identified either by its layout name.

For instance, the loader icon can be easily inserted like this:
```php
<?= $blockRenderer->html('loki.checkout.utils.loader-small') ?>
```

Similarly, a block can be rendered by passing its template:
```php
<?= $blockRenderer->html('form/field/text/script.phtml', $block) ?>
```

The utitity has two main rendering methods:

- `html(string $blockIdentifier, ?AbstractBlock $parentBlock = null, array $data = []): AbstractBlock`
- `get(string $blockIdentifier, ?AbstractBlock $parentBlock = null, array $data = []): AbstractBlock`

Both methods boil down to the same thing - instantiating a block. The `html()` method actually calls upon the `get()` method to retrieve a block object and then calls upon the `toHtml()` method of that object (so `$block->toHtml()`).

Note that the `$blockRenderer` utility does not take the layout hierarchy into account. It assumes that a block is defined somewhere with a specific block name (in the XML layout: `<block name="foobar" />`) or that there is a PHTML template somewhere available. This means that you might still want to call upon child blocks regularly as well:

```php
<?= $block->getChildHtml($childAlias) ?>
```

## Adding more block prefixes
The class `Loki\Components\Observer\AssignAdditionalBlockVariables` its constructor argument `blockPrefixes` defines which blocks automatically get these template variables inserted. To add your own block, either use the existing prefix `loki` or add your own block prefix or block name:

```xml
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Loki\Components\Observer\AssignAdditionalBlockVariables">
        <arguments>
            <argument name="blockPrefixes" xsi:type="array">
                <item name="foobar" xsi:type="string">foobar</item>
            </argument>
        </arguments>
    </type>
</config>
```