Merge pull request #892 from storytold/fix/787-precise-export

Fix #787: raster exports keep translucent edges over opaque art opaque

Cargo.toml

@@ -54,7 +54,7 @@ wasmi = { version = "2.0.0", default-features = false, features = ["std", "valid
 wat = "1.228"
 
 # rendering / formats
-vello_cpu = "0.2"
+vello_cpu = { version = "0.2", features = ["f32_pipeline"] }
 image = { version = "0.25", default-features = false, features = ["png", "jpeg", "webp", "gif", "tiff", "bmp"] }
 usvg = "0.48"
 krilla = "0.8"

crates/engine/src/cmd/webexport.rs

@@ -582,7 +582,8 @@ pub fn render(doc: &Document, s: &WebSettings) -> std::result::Result<WebRender,
     let doc = doc.without_edit_modes();
     let (region, scale) = region(&doc, s)?;
     let page = (doc.setup.background == vectorcraft_doc::Background::White).then_some([255; 4]);
-    let opts = vectorcraft_render::RenderOptions { background: page, skip_templates: true, anti_alias: s.anti_alias, ..Default::default() };
+    let opts =
+        vectorcraft_render::RenderOptions { background: page, skip_templates: true, anti_alias: s.anti_alias, precise: true, ..Default::default() };
     let img = vectorcraft_render::Renderer::new().render_region_with(&doc, region, scale, &opts);
     Ok(WebRender { rgba: img.to_straight(), width: img.width, height: img.height, region, scale })
 }

crates/render/src/encode/mod.rs

@@ -87,7 +87,7 @@ impl RasterExportOptions {
     }
 
     /// What the renderer draws for `format`: template layers and guides left out, over the background
-    /// (white for a JPEG or a flat PSD without one).
+    /// (white for a JPEG or a flat PSD without one), composited in floating point.
     pub fn render_options(&self, format: RasterFormat) -> RenderOptions {
         let flat = format == RasterFormat::Jpeg || (format == RasterFormat::Psd && !self.psd.layers);
         let background = self.background.or(flat.then_some([255; 3]));
@@ -95,6 +95,8 @@ impl RasterExportOptions {
             background: background.map(|[r, g, b]| [r, g, b, 255]),
             skip_templates: true,
             anti_alias: self.anti_alias,
+            // Opaque art stays exactly opaque where translucent edges cross it (#787).
+            precise: true,
             ..Default::default()
         }
     }

crates/render/src/encode/tests.rs

@@ -110,6 +110,44 @@ fn backgrounds_are_opaque_or_transparent() {
     assert_eq!(webp.get_pixel(0, 0).0, [0, 0, 0, 255]);
 }
 
+/// #787: translucent art over opaque art (or a background) stays exactly opaque, its anti-aliased
+/// edges too, so the file is written as RGB.
+#[test]
+fn translucent_edges_over_opaque_art_stay_opaque() {
+    let mut d = Document::new(100.0, 100.0);
+    let l = d.layers[0].id;
+    let under = Node::path(
+        d.alloc_id(),
+        shapes::rectangle(Rect::new(0.0, 0.0, 100.0, 100.0)),
+        Appearance::basic(Paint::solid(Color::BLACK), Paint::None, 0.0),
+    );
+    let mut over =
+        Node::path(d.alloc_id(), shapes::ellipse(Rect::new(10.0, 10.0, 90.0, 90.0)), Appearance::basic(Paint::solid(Color::WHITE), Paint::None, 0.0));
+    over.opacity = 0.5;
+    let only_over = {
+        let mut d = d.clone();
+        d.insert(Some(l), 0, over.clone()).unwrap();
+        d
+    };
+    d.insert(Some(l), 0, under).unwrap();
+    d.insert(Some(l), 1, over).unwrap();
+    // Over a black background at 72 ppi, and over an opaque rectangle at a scale that puts the
+    // edges on fractions of a pixel.
+    for (doc, o) in [
+        (&only_over, RasterExportOptions { background: Some([0, 0, 0]), ..Default::default() }),
+        (&d, RasterExportOptions { ppi: 72.0 * 0.3515625, ..Default::default() }),
+    ] {
+        let png = Renderer::new().export_region(doc, doc.artboards[0].rect, RasterFormat::Png, &o).unwrap();
+        let img = image::load_from_memory(&png).unwrap().to_rgba8();
+        let below: Vec<_> = img.pixels().filter(|p| p[3] < 255).collect();
+        assert!(below.is_empty(), "ppi {}: {} pixels below alpha 255, e.g. {:?}", o.ppi, below.len(), below.first());
+        assert_eq!(png[25], 2, "IHDR colour type: RGB");
+    }
+    // The inside is half white over black.
+    let img = export(&only_over, RasterFormat::Png, &RasterExportOptions { background: Some([0, 0, 0]), ..Default::default() });
+    assert!(img.get_pixel(50, 50).0[..3].iter().all(|c| (127..=128).contains(c)), "{:?}", img.get_pixel(50, 50));
+}
+
 #[test]
 fn interlaced_export_decodes_to_the_same_pixels() {
     let d = circle_doc();

crates/render/src/group.rs

@@ -137,7 +137,7 @@ impl Renderer {
     fn flatten(&mut self, ctx: &mut RenderContext, r: Region) -> Arc<Pixmap> {
         ctx.flush();
         let mut all = Pixmap::new(ctx.width(), ctx.height());
-        ctx.render(&mut all, &mut self.resources);
+        ctx.render_with(&mut all, &mut self.resources, self.raster);
         ctx.reset();
         let crop = if (r.x, r.y, r.w, r.h) == (0, 0, all.width(), all.height()) {
             None
@@ -171,7 +171,7 @@ impl Renderer {
         (self.nested, self.backdrop, self.clip_paths) = outer;
         ctx.flush();
         let mut pm = Pixmap::new(r.w, r.h);
-        ctx.render(&mut pm, &mut self.resources);
+        ctx.render_with(&mut pm, &mut self.resources, self.raster);
         pm
     }
 

crates/render/src/lib.rs

@@ -110,6 +110,10 @@ pub struct RenderOptions {
     /// Screen view in isolation mode: the isolated group or layer. Everything around it draws
     /// dimmed ([`ISOLATION_DIM`]).
     pub isolated: Option<NodeId>,
+    /// Composite in floating point (exports): translucent art over opaque art comes out exactly
+    /// opaque, where 8-bit compositing leaves alpha 254 on some anti-aliased edges (#787). Off,
+    /// the faster 8-bit pipeline (the canvas).
+    pub precise: bool,
 }
 
 /// The opacity of the art around an isolated group or layer.
@@ -181,6 +185,7 @@ impl Default for RenderOptions {
             trace_views: false,
             smooth_images: true,
             isolated: None,
+            precise: false,
         }
     }
 }
@@ -362,6 +367,9 @@ pub struct Renderer {
     /// Inline graphics being drawn inside inline graphics (a symbol whose art holds text showing
     /// it): drawing stops at [`MAX_INLINE_DEPTH`].
     inline_depth: u32,
+    /// How the frame being drawn is rasterized ([`RenderOptions::precise`]): its offscreen groups,
+    /// masks and patterns too.
+    raster: vello_cpu::RasterizerSettings,
     /// [`RenderOptions::isolated`]'s layers and groups, from the top layer down to it, for the
     /// frame (`stamp`) and document they were found in.
     isolation: Option<(u64, usize, NodeId, Vec<NodeId>)>,
@@ -453,6 +461,7 @@ impl Renderer {
             adjusted: Default::default(),
             dim_images: None,
             inline_depth: 0,
+            raster: vello_cpu::RasterizerSettings::default(),
             isolation: None,
             isolation_settled: false,
         }
@@ -532,6 +541,8 @@ impl Renderer {
         };
         // `reset` keeps the threshold of the previous render: set it every time.
         ctx.set_aliasing_threshold(opts.anti_alias.threshold());
+        let render_mode = if opts.precise { vello_cpu::RenderMode::OptimizeQuality } else { vello_cpu::RenderMode::OptimizeSpeed };
+        self.raster = vello_cpu::RasterizerSettings { render_mode, ..Default::default() };
         if let Some(bg) = opts.background {
             ctx.set_transform(Affine::IDENTITY);
             ctx.set_paint(f.ink.fixed(bg));
@@ -560,7 +571,7 @@ impl Renderer {
         }
         ctx.flush();
         let mut pm = Pixmap::new(w, h);
-        ctx.render(&mut pm, &mut self.resources);
+        ctx.render_with(&mut pm, &mut self.resources, self.raster);
         if threads == 0 {
             self.ctx_st = Some(ctx);
         } else {
@@ -795,7 +806,7 @@ impl Renderer {
         (self.knockout, self.nested, self.backdrop, self.clip_paths) = outer;
         mctx.flush();
         let mut pm = Pixmap::new(w, h);
-        mctx.render(&mut pm, &mut self.resources);
+        mctx.render_with(&mut pm, &mut self.resources, self.raster);
         pm.data().iter().map(|p| mask_value(p.r, p.g, p.b, p.a, m.clip, m.invert)).collect()
     }
 

crates/render/src/pattern.rs

@@ -88,7 +88,7 @@ fn rasterize(r: &mut Renderer, doc: &Document, def: &PatternDef, region: Rect, w
     }
     ctx.flush();
     let mut pm = Pixmap::new(w, h);
-    ctx.render(&mut pm, &mut r.resources);
+    ctx.render_with(&mut pm, &mut r.resources, r.raster);
     pm
 }