Renamed clear_color to base_color; addressed review comments

examples/headless/src/main.rs

@@ -92,15 +92,15 @@ async fn render(mut scenes: SceneSet, index: usize, args: &Args) -> Result<()> {
     let mut builder = SceneBuilder::for_fragment(&mut fragment);
     let example_scene = &mut scenes.scenes[index];
     let mut text = SimpleText::new();
-    let mut params = SceneParams {
+    let mut scene_params = SceneParams {
         time: args.time.unwrap_or(0.),
         text: &mut text,
         resolution: None,
     };
-    (example_scene.function)(&mut builder, &mut params);
+    (example_scene.function)(&mut builder, &mut scene_params);
     builder.finish();
     let mut transform = Affine::IDENTITY;
-    let (width, height) = if let Some(resolution) = params.resolution {
+    let (width, height) = if let Some(resolution) = scene_params.resolution {
         let ratio = resolution.x / resolution.y;
         let (new_width, new_height) = match (args.x_resolution, args.y_resolution) {
             (None, None) => (resolution.x.ceil() as u32, resolution.y.ceil() as u32),
@@ -126,8 +126,11 @@ async fn render(mut scenes: SceneSet, index: usize, args: &Args) -> Result<()> {
             (Some(x), Some(y)) => (x.try_into()?, y.try_into()?),
         }
     };
-    let params = vello::RenderParams {
-        clear_color: vello::peniko::Color::BLACK,
+    let render_params = vello::RenderParams {
+        base_color: args
+            .args
+            .get_base_color()?
+            .unwrap_or(vello::peniko::Color::BLACK),
         width,
         height,
     };
@@ -152,7 +155,7 @@ async fn render(mut scenes: SceneSet, index: usize, args: &Args) -> Result<()> {
     });
     let view = target.create_view(&wgpu::TextureViewDescriptor::default());
     renderer
-        .render_to_texture(&device, &queue, &scene, &view, &params)
+        .render_to_texture(&device, &queue, &scene, &view, &render_params)
         .or_else(|_| bail!("Got non-Send/Sync error from rendering"))?;
     // (width * 4).next_multiple_of(256)
     let padded_byte_width = {

examples/scenes/src/lib.rs

@@ -5,7 +5,7 @@ mod svg;
 mod test_scenes;
 use std::path::PathBuf;
 
-use anyhow::Result;
+use anyhow::{anyhow, Result};
 use clap::{Args, Subcommand};
 use download::Download;
 pub use simple_text::SimpleText;
@@ -13,7 +13,7 @@ pub use simple_text::SimpleText;
 pub use svg::{default_scene, scene_from_files};
 pub use test_scenes::test_scenes;
 
-use vello::{kurbo::Vec2, SceneBuilder};
+use vello::{kurbo::Vec2, peniko::Color, SceneBuilder};
 
 pub struct SceneParams<'a> {
     pub time: f64,
@@ -46,6 +46,12 @@ pub struct Arguments {
     #[arg(help_heading = "Scene Selection", global(false))]
     /// The svg files paths to render
     svgs: Option<Vec<PathBuf>>,
+    #[arg(help_heading = "Render Parameters")]
+    #[arg(long, global(false))]
+    /// The base color applied as the blend background to the rasterizer.
+    /// Format is CSS style hexidecimal (#RGB, #RGBA, #RRGGBB, #RRGGBBAA) or
+    /// an SVG color name such as "aliceblue"
+    base_color: Option<String>,
     #[clap(subcommand)]
     command: Option<Command>,
 }
@@ -79,6 +85,17 @@ impl Arguments {
             .map(Some)
         }
     }
+
+    pub fn get_base_color(&self) -> Result<Option<Color>> {
+        self.base_color.as_ref().map_or_else(
+            || Ok(None),
+            |s| {
+                Color::parse(&s)
+                    .ok_or_else(|| anyhow!("malformed color: {}", s))
+                    .map(Some)
+            },
+        )
+    }
 }
 
 impl Command {

examples/with_bevy/src/main.rs

@@ -47,7 +47,7 @@ fn render_scenes(
     for scene in &mut scenes {
         let gpu_image = gpu_images.get(&scene.1).unwrap();
         let params = vello::RenderParams {
-            clear_color: vello::peniko::Color::AQUAMARINE,
+            base_color: vello::peniko::Color::AQUAMARINE,
             width: gpu_image.size.x as u32,
             height: gpu_image.size.y as u32,
         };

examples/with_winit/src/main.rs

@@ -17,10 +17,7 @@
 use std::time::Instant;
 
 use anyhow::Result;
-use clap::{
-    builder::{PossibleValuesParser, TypedValueParser as _},
-    CommandFactory, Parser,
-};
+use clap::{CommandFactory, Parser};
 use scenes::{SceneParams, SceneSet, SimpleText};
 use vello::SceneFragment;
 use vello::{
@@ -53,52 +50,18 @@ struct Args {
     /// Switch between scenes with left and right arrow keys
     #[arg(long)]
     scene: Option<i32>,
-    #[arg(
-        long,
-        default_value_t = ClearColor::Black,
-        value_parser = PossibleValuesParser::new(["black", "white", "aquamarine", "crimson"])
-            .map(|s| s.parse::<ClearColor>().unwrap())
-    )]
-    clear_color: ClearColor,
+    /// The base color used as the
     #[command(flatten)]
     args: scenes::Arguments,
 }
 
-#[derive(Debug, Clone)]
-enum ClearColor {
-    Black,
-    White,
-    Crimson,
-    Aquamarine,
-}
-
-impl std::fmt::Display for ClearColor {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        let s = match self {
-            Self::Black => "black",
-            Self::White => "white",
-            Self::Crimson => "crimson",
-            Self::Aquamarine => "aquamarine",
-        };
-        s.fmt(f)
-    }
-}
-
-impl std::str::FromStr for ClearColor {
-    type Err = String;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        match s {
-            "black" => Ok(Self::Black),
-            "white" => Ok(Self::White),
-            "crimson" => Ok(Self::Crimson),
-            "aquamarine" => Ok(Self::Aquamarine),
-            _ => Err(format!("invalid color: {s}")),
-        }
-    }
-}
-
-async fn run(event_loop: EventLoop<UserEvent>, window: Window, args: Args, mut scenes: SceneSet) {
+async fn run(
+    event_loop: EventLoop<UserEvent>,
+    window: Window,
+    args: Args,
+    base_color: Color,
+    mut scenes: SceneSet,
+) {
     use winit::{event::*, event_loop::ControlFlow};
     let mut render_cx = RenderContext::new().unwrap();
     let size = window.inner_size();
@@ -120,12 +83,6 @@ async fn run(event_loop: EventLoop<UserEvent>, window: Window, args: Args, mut s
     if let Some(set_scene) = args.scene {
         scene_ix = set_scene;
     }
-    let clear_color = match args.clear_color {
-        ClearColor::Black => Color::BLACK,
-        ClearColor::White => Color::WHITE,
-        ClearColor::Crimson => Color::CRIMSON,
-        ClearColor::Aquamarine => Color::AQUAMARINE,
-    };
     let mut prev_scene_ix = scene_ix - 1;
     event_loop.run(move |event, _, control_flow| match event {
         Event::WindowEvent {
@@ -207,7 +164,7 @@ async fn run(event_loop: EventLoop<UserEvent>, window: Window, args: Args, mut s
             let device_handle = &render_cx.devices[surface.dev_id];
 
             let render_params = vello::RenderParams {
-                clear_color,
+                base_color,
                 width,
                 height,
             };
@@ -300,6 +257,7 @@ fn main() -> Result<()> {
     env_logger::init();
     let args = Args::parse();
     let scenes = args.args.select_scene_set(|| Args::command())?;
+    let base_color = args.args.get_base_color()?.unwrap_or(Color::BLACK);
     if let Some(scenes) = scenes {
         #[cfg(not(target_arch = "wasm32"))]
         {
@@ -317,7 +275,7 @@ fn main() -> Result<()> {
                 .with_title("Vello demo")
                 .build(&event_loop)
                 .unwrap();
-            pollster::block_on(run(event_loop, window, args, scenes));
+            pollster::block_on(run(event_loop, window, args, base_color, scenes));
         }
         #[cfg(target_arch = "wasm32")]
         {
@@ -337,7 +295,7 @@ fn main() -> Result<()> {
                 .and_then(|doc| doc.body())
                 .and_then(|body| body.append_child(&web_sys::Element::from(canvas)).ok())
                 .expect("couldn't append canvas to document body");
-            wasm_bindgen_futures::spawn_local(run(event_loop, window, args, scenes));
+            wasm_bindgen_futures::spawn_local(run(event_loop, window, args, base_color, scenes));
         }
     }
     Ok(())

shader/fine.wgsl

@@ -188,7 +188,7 @@ fn main(
 #ifdef full
     var rgba: array<vec4<f32>, PIXELS_PER_THREAD>;
     for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) {
-        rgba[i] = unpack4x8unorm(config.clear_color).wzyx;
+        rgba[i] = unpack4x8unorm(config.base_color).wzyx;
     }
     var blend_stack: array<array<u32, PIXELS_PER_THREAD>, BLEND_STACK_SPLIT>;
     var clip_depth = 0u;

shader/shared/config.wgsl

@@ -10,7 +10,7 @@ struct Config {
     // The initial color applied to the pixels in a tile during the fine stage.
     // This is only used in the full pipeline. The format is packed RGBA8 in MSB
     // order.
-    clear_color: u32,
+    base_color: u32,
 
     n_drawobj: u32,
     n_path: u32,

src/encoding/packed.rs

@@ -48,7 +48,8 @@ pub struct Layout {
     pub linewidth_base: u32,
 }
 
-/// Scene configuration.
+/// Scene configuration. This data structure must be kept in sync with the definition in
+/// shaders/shared/config.wgsl.
 #[derive(Clone, Copy, Debug, Default, Zeroable, Pod)]
 #[repr(C)]
 pub struct Config {
@@ -60,8 +61,8 @@ pub struct Config {
     pub target_width: u32,
     /// Height of the target in pixels.
     pub target_height: u32,
-    /// The initial background color applied to the target
-    pub clear_color: u32,
+    /// The base background color applied to the target before any blends.
+    pub base_color: u32,
     /// Layout of packed scene data.
     pub layout: Layout,
     /// Size of binning buffer allocation (in u32s).

src/lib.rs

@@ -56,7 +56,7 @@ pub struct Renderer {
 pub struct RenderParams {
     /// The background color applied to the target. This value is only applicable to the full
     /// pipeline.
-    pub clear_color: peniko::Color,
+    pub base_color: peniko::Color,
 
     /// Dimensions of the rasterization target
     pub width: u32,
@@ -64,7 +64,7 @@ pub struct RenderParams {
 }
 
 impl Renderer {
-    /// Creates a new renderer for the specified device with default options.
+    /// Creates a new renderer for the specified device.
     pub fn new(device: &Device) -> Result<Self> {
         let mut engine = Engine::new();
         let shaders = shaders::full_shaders(device, &mut engine)?;

src/render.rs

@@ -55,6 +55,8 @@ const BIN_HEADER_SIZE: u64 = 8;
 const TILE_SIZE: u64 = 8;
 const SEGMENT_SIZE: u64 = 24;
 
+// This data structure must be kept in sync with encoding::Config and the definition in
+// shaders/shared/config.wgsl.
 #[repr(C)]
 #[derive(Clone, Copy, Debug, Default, Zeroable, Pod)]
 struct Config {
@@ -62,7 +64,7 @@ struct Config {
     height_in_tiles: u32,
     target_width: u32,
     target_height: u32,
-    clear_color: u32,
+    base_color: u32,
     n_drawobj: u32,
     n_path: u32,
     n_clip: u32,
@@ -264,7 +266,7 @@ impl Render {
             height_in_tiles: new_height / 16,
             target_width: params.width,
             target_height: params.height,
-            clear_color: params.clear_color.to_premul_u32(),
+            base_color: params.base_color.to_premul_u32(),
             binning_size: self.binning_info_size - info_size,
             tiles_size: self.tiles_size,
             segments_size: self.segments_size,