Custom Responsive URL Generator

ResponsiveImageUrlGeneratorInterface decides what URL each responsive breakpoint's srcset candidate points to. There are three built-in options, resolved in this priority order:

1. an explicit responsive_strategy.generator — always wins;
2. VariantResponsiveImageUrlGenerator, automatically active once variant_store.storage is configured (this is what makes the Variant pipeline actually produce resized files);
3. DefaultResponsiveImageUrlGenerator — an identity passthrough, used when neither of the above applies.

Implement your own if you already have an external image-resizing service (a SaaS image CDN, an existing internal resizer) and don't want the Variant pipeline generating files at all.

The interface

namespace Tito10047\ProgressiveImageBundle\UrlGenerator;

interface ResponsiveImageUrlGeneratorInterface
{
    public function generateUrl(string $path, int $targetW, ?int $targetH, ?string $pointInterest = null, array $context = []): string;
}

Called once per resolved breakpoint/retina-multiplier/negotiated-format combination by ResponsiveAttributeGenerator while building a <picture>'s srcset.

Example: an external image CDN

namespace App\Image;

use Tito10047\ProgressiveImageBundle\UrlGenerator\ResponsiveImageUrlGeneratorInterface;

final class ImgixUrlGenerator implements ResponsiveImageUrlGeneratorInterface
{
    public function __construct(private string $imgixHost)
    {
    }

    public function generateUrl(string $path, int $targetW, ?int $targetH, ?string $pointInterest = null, array $context = []): string
    {
        $query = ['w' => $targetW];
        if (null !== $targetH) {
            $query['h'] = $targetH;
            $query['fit'] = 'crop';
        }

        return rtrim($this->imgixHost, '/').'/'.ltrim($path, '/').'?'.http_build_query($query);
    }
}

Wiring it in

// config/services.php
$container->services()
    ->set(App\Image\ImgixUrlGenerator::class)
    ->arg('$imgixHost', 'https://your-source.imgix.net');

# config/packages/progressive_image.yaml
progressive_image:
    responsive_strategy:
        generator: App\Image\ImgixUrlGenerator

Setting this makes the bundle skip the Variant pipeline for URL generation entirely — no files are generated locally, only URLs. variant_store.storage can stay unset in that case, unless you still want the wait/pending flow for some other purpose.