PNG Output does not support transparency

[manuel5975p]

Description

Synopsis

Setting no background results in a transparent svg, but opaquely white png.

Example

#lorem(20)

Results in

SVG

---

PNG

Reproduction URL

No response

Operating system

Web app, Linux

Typst version

• I am using the latest version of Typst

[benlubas]

So, this works:

diff --git a/crates/typst-cli/src/compile.rs b/crates/typst-cli/src/compile.rs
index e145a820..a3b72022 100644
--- a/crates/typst-cli/src/compile.rs
+++ b/crates/typst-cli/src/compile.rs
@@ -331,7 +331,7 @@ fn export_image_page(
 ) -> StrResult<()> {
     match fmt {
         ImageExportFormat::Png => {
-            let pixmap = typst_render::render(frame, command.ppi / 72.0, Color::WHITE);
+            let pixmap = typst_render::render(frame, command.ppi / 72.0, Color::WHITE.with_alpha(0.));
             let buf = pixmap
                 .encode_png()
                 .map_err(|err| eco_format!("failed to encode PNG file ({err})"))?;

it lets me produce an image like this:

by running typst compile test.typ test.png.

With this change, #set page(fill: white) will return the white background with no issues.

It does change a default though, I'm not sure what people (maintainers) think about that?

[laurmaedje]

There was some discussion about this on the Discord, starting with this message: https://discord.com/channels/1054443721975922748/1088371867913572452/1237388946946658304

[benlubas]

@laurmaedje thanks, am I correct in that this

I wonder if it would make sense to get the color for the png background from the #page.fill property? And just keep white if its not there?

is the preferred solution then? and someone said they would work on it and then disappeared for a bit?

I might just try and do it myself if that's an acceptable solution

[benlubas]

Have something that appears to work, but it's a total shot in the dark from me b/c I've never worked on this project before. I will open a PR later tonight after I eat dinner.