Color/Brush override about vello_svg

[simbleau]

No, there isn't currently.

This crate essentially exposes one method to translate an SVG into a Vello 'Scene'.

I think of a Scene as "write-only". There's no way to go back and recolor it.

I'm not sure what API would be suitable, how would you go about it?

[jrmoulton]

        let brush_present = brush.is_some();

        let mut scene = Scene::new();
        if let Some(brush) = brush {
            let rect = Rect::from_origin_size(
                (0., 0.),
                (svg_size.width() as f64, svg_size.height() as f64),
            );
            scene.fill(Fill::NonZero, Affine::IDENTITY, brush, None, &rect);
            scene.push_layer(
                vello::peniko::BlendMode {
                    mix: Mix::Multiply,
                    compose: Compose::SrcOver,
                },
                1.,
                Affine::IDENTITY,
                &rect,
            );
        }
        vello_svg::render_tree(&mut scene, svg.tree);

        if brush_present {
            scene.pop_layer();
        }

I am trying to come up with a way to do this by drawing the override brush color to the background and then using the svg layer as an alpha mask for the background. But I can't figure it out / don't know if it is possible by using a layer with a blend mode.

[jrmoulton]

  if let Some(brush) = brush {
      scene.push_layer(
          vello::peniko::BlendMode {
              mix: Mix::Normal,
              compose: Compose::SrcOver,
          },
          1.0,
          Affine::IDENTITY,
          &Rect::from_origin_size(
              (0., 0.),
              (svg_size.width() as f64, svg_size.height() as f64),
          ),
      );

      vello_svg::render_tree(&mut scene, svg.tree);

      scene.push_layer(
          vello::peniko::BlendMode {
              mix: Mix::Clip,
              compose: Compose::SrcIn,
          },
          1.0,
          Affine::IDENTITY,
          &Rect::from_origin_size(
              (0., 0.),
              (svg_size.width() as f64, svg_size.height() as f64),
          ),
      );

      scene.fill(Fill::NonZero, Affine::IDENTITY, brush.into(), None, &rect);
      scene.pop_layer();

      scene.pop_layer();
  } else {
      vello_svg::render_tree(&mut scene, svg.tree);
  }

I was finally able to figure it out. This will override the svg color, essentially using the svg as an alpha mask

[simbleau]

Great! Does this need to be an addition to vello_svg then? You seem to have a workaround that uses vello_svg as intended.

[jrmoulton]

Probably doesn't need to be an addition to vello_svg. I think this is better solved by adding some docs on how to create an alpha mask with Vello. I'll look into adding that