Merge pull request #885 from switch87/feat/784-transparent-png-export

apps/deckcraft-cli/src/help.rs

@@ -19,15 +19,16 @@ The shapes of one slide, with their ids, boxes and text, come from the slide.ins
     },
     Subcommand {
         name: "render",
-        usage: "render (FILE | --sample) [--slide N | --all] [--scale S] [--edit] OUT",
+        usage: "render (FILE | --sample) [--slide N | --all] [--scale S] [--edit] [--transparent] OUT",
         summary: "draw slides as PNG images",
         details: "Draws slides of FILE, or of the sample presentation with --sample, as PNG images. FILE comes first;
 OUT is the image to write. With --all, OUT is a folder that gets one slide-01.png, slide-02.png… per
 slide. Prints each image's path and size.
 
-  --slide N   the slide at index N; indices start at 0, and 0 is the default
-  --scale S   pixels per point, 2 by default: a 960×540 slide becomes 1920×1080
-  --edit      draw what the editor shows: placeholder prompts and their dashed outlines
+  --slide N        the slide at index N; indices start at 0, and 0 is the default
+  --scale S        pixels per point, 2 by default: a 960×540 slide becomes 1920×1080
+  --edit           draw what the editor shows: placeholder prompts and their dashed outlines
+  --transparent    leave the slide background out, so only what is on the slide is drawn
 
   deckcraft-cli render deck.deckcraft --slide 2 slide-3.png",
     },

apps/deckcraft-cli/src/main.rs

@@ -260,11 +260,13 @@ fn render(args: &[String]) -> Result<(), String> {
     let mut all = false;
     let mut scale = 2.0;
     let mut edit = false;
+    let mut transparent = false;
     let mut out = None;
     let mut it = args.iter();
     while let Some(a) = it.next() {
         match a.as_str() {
             "--sample" => sample = true,
+            "--transparent" => transparent = true,
             "--slide" => slide = Some(it.next().and_then(|v| v.parse().ok()).ok_or("--slide needs a number")?),
             "--all" => all = true,
             "--edit" => edit = true,
@@ -297,7 +299,7 @@ fn render(args: &[String]) -> Result<(), String> {
         std::fs::create_dir_all(&out).map_err(|e| format!("{out}: {e}"))?;
     }
     for i in list {
-        let (png, w, h) = deckcraft_engine::cmd::file::render_png(&st.doc, i, scale, edit);
+        let (png, w, h) = deckcraft_engine::cmd::file::render_png_with(&st.doc, i, scale, edit, transparent);
         let path = if all { format!("{out}/slide-{:02}.png", i + 1) } else { out.clone() };
         std::fs::write(&path, png).map_err(|e| format!("{path}: {e}"))?;
         outln!("{path} ({w}×{h})");
@@ -696,6 +698,21 @@ mod tests {
         }
     }
 
+    /// `render --transparent` leaves the slide background out (#784): the corner is transparent.
+    #[test]
+    fn render_transparent_leaves_the_background_out() {
+        let dir = std::env::temp_dir().join(format!("deckcraft-cli-transparent-{}", std::process::id()));
+        std::fs::create_dir_all(&dir).unwrap();
+        let alpha = |path: &std::path::Path| deckcraft_engine::render::decode_image(&std::fs::read(path).unwrap()).unwrap().get_pixel(1, 1).0[3];
+        let opaque = dir.join("opaque.png");
+        render(&args(&["--sample", "--scale", "0.25", &opaque.to_string_lossy()])).unwrap();
+        assert_eq!(alpha(&opaque), 255);
+        let clear = dir.join("clear.png");
+        render(&args(&["--sample", "--transparent", "--scale", "0.25", &clear.to_string_lossy()])).unwrap();
+        assert_eq!(alpha(&clear), 0);
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
     /// `run --export OUT.gif --export-params JSON` and `convert IN OUT.gif` write animated GIFs.
     #[test]
     fn exports_an_animated_gif() {