[flutter_svg] Proposal: Add imageBuilder property to SvgPicture for post-load decoration

[janpierry]

Use case

Currently, SvgPicture provides placeholderBuilder and errorBuilder, but it lacks a "success" builder equivalent to imageBuilder in CachedNetworkImage.

If a developer wants to apply a decoration (like a Border, BoxShadow, or BorderRadius) specifically to the resulting image, they must wrap the SvgPicture widget in a Container or DecoratedBox. However, this decoration is then visible even when the image is loading (placeholder) or when it fails (error).

Proposal

It would be really useful to have a imageBuilder property added to SvgPicture constructors. This builder should only trigger once the SVG has been successfully parsed and is ready to be painted.

Proposed API

SvgPicture.asset(
  'assets/icons/logo.svg',
  imageBuilder: (BuildContext context, Widget image) {
    return Container(
      decoration: BoxDecoration(
        border: Border.all(color: Colors.blue, width: 2),
        borderRadius: BorderRadius.circular(8),
      ),
      child: image,
    );
  },
  placeholderBuilder: (context) => CircularProgressIndicator(),
)