servo/components/canvas/vello_cpu_backend.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

use std::cell::RefCell;
use std::collections::HashMap;
use std::sync::Arc;

use canvas_traits::canvas::{
    CompositionOptions, CompositionOrBlending, CompositionStyle, FillOrStrokeStyle, FillRule,
    LineOptions, Path, ShadowOptions, TextRun,
};
use compositing_traits::SerializableImageData;
use euclid::default::{Point2D, Rect, Size2D, Transform2D};
use fonts::FontIdentifier;
use ipc_channel::ipc::IpcSharedMemory;
use kurbo::Shape;
use pixels::{Snapshot, SnapshotAlphaMode, SnapshotPixelFormat};
use vello_cpu::{kurbo, peniko};
use webrender_api::{ImageDescriptor, ImageDescriptorFlags};

use crate::backend::{Convert, GenericDrawTarget};
use crate::canvas_data::Filter;

thread_local! {
    /// The shared font cache used by all canvases that render on a thread.
    static SHARED_FONT_CACHE: RefCell<HashMap<FontIdentifier, peniko::Font>> = RefCell::default();
}

#[derive(Clone, Copy, Debug, PartialEq, PartialOrd)]
enum State {
    /// Scene is drawing. It will be consumed when rendered.
    Drawing,
    /// Scene is already rendered
    /// Before next draw we need to put current rendering
    /// in the background by calling [`VelloCPUDrawTarget::ensure_drawing`].
    Rendered,
}

pub(crate) struct VelloCPUDrawTarget {
    /// Because this is stateful context
    /// caller cannot assume anything about transform, paint, stroke,
    /// so it should provide it's own used by each command
    /// but it can assume paint_transform to be identity
    /// and fill rule to be `peniko::Fill::NonZero`
    ///
    /// This is because paint_transform is rarely set,
    /// so it's cheaper to always reset it after use.
    ctx: vello_cpu::RenderContext,
    pixmap: vello_cpu::Pixmap,
    clips: Vec<Path>,
    state: State,
}

impl VelloCPUDrawTarget {
    fn with_composition(
        &mut self,
        composition_operation: CompositionOrBlending,
        f: impl FnOnce(&mut Self),
    ) {
        // Fast-path for default and most common composition operation
        if composition_operation == CompositionOrBlending::Composition(CompositionStyle::SourceOver)
        {
            f(self);
            return;
        }
        self.ctx.push_blend_layer(composition_operation.convert());
        f(self);
        self.ctx.pop_layer();
    }

    fn ignore_clips(&mut self, f: impl FnOnce(&mut Self)) {
        // pop all clip layers
        for _ in &self.clips {
            self.ctx.pop_layer();
        }
        f(self);
        // push all clip layers back
        for path in &self.clips {
            self.ctx.push_clip_layer(&path.0);
        }
    }

    fn ensure_drawing(&mut self) {
        match self.state {
            State::Drawing => {},
            State::Rendered => {
                self.ignore_clips(|self_| {
                    self_.ctx.set_transform(kurbo::Affine::IDENTITY);
                    self_.ctx.set_paint(vello_cpu::Image {
                        source: vello_cpu::ImageSource::Pixmap(Arc::new(self_.pixmap.clone())),
                        x_extend: peniko::Extend::Pad,
                        y_extend: peniko::Extend::Pad,
                        quality: peniko::ImageQuality::Low,
                    });
                    self_.ctx.fill_rect(&kurbo::Rect::from_origin_size(
                        (0., 0.),
                        self_.size().cast(),
                    ));
                });
                self.state = State::Drawing;
            },
        }
    }

    fn pixmap(&mut self) -> &[u8] {
        if self.state == State::Drawing {
            self.ignore_clips(|self_| {
                self_.ctx.flush();
                self_.ctx.render_to_pixmap(&mut self_.pixmap);
                self_.ctx.reset();
                self_.state = State::Rendered;
            });
        }

        self.pixmap.data_as_u8_slice()
    }

    fn size(&self) -> Size2D<u32> {
        Size2D::new(self.ctx.width(), self.ctx.height()).cast()
    }

    fn is_viewport_cleared(&mut self, rect: &Rect<f32>, transform: Transform2D<f64>) -> bool {
        let transformed_rect = transform.outer_transformed_rect(&rect.cast());
        if transformed_rect.is_empty() {
            return false;
        }
        let viewport: Rect<f64> = Rect::from_size(self.get_size().cast());
        let Some(clip) = self.clips.iter().try_fold(viewport, |acc, e| {
            acc.intersection(&e.0.bounding_box().into())
        }) else {
            // clip makes no visible side effects
            return false;
        };
        transformed_rect.cast().contains_rect(&viewport) && // whole viewport is cleared
            clip.contains_rect(&viewport) // viewport is not clipped
    }
}

impl GenericDrawTarget for VelloCPUDrawTarget {
    type SourceSurface = Arc<vello_cpu::Pixmap>;

    fn new(size: Size2D<u32>) -> Self {
        let size = size.cast();
        Self {
            ctx: vello_cpu::RenderContext::new(size.width, size.height),
            pixmap: vello_cpu::Pixmap::new(size.width, size.height),
            clips: Vec::new(),
            state: State::Rendered,
        }
    }

    fn clear_rect(&mut self, rect: &Rect<f32>, transform: Transform2D<f64>) {
        // vello_cpu RenderingContext only ever grows,
        // so we need to use every opportunity to shrink it
        if self.is_viewport_cleared(rect, transform) {
            self.ctx.reset();
            self.clips.clear(); // no clips are affecting rendering
            self.state = State::Drawing;
            return;
        }
        self.ensure_drawing();
        let rect: kurbo::Rect = rect.cast().into();
        let mut clip_path = rect.to_path(0.1);
        clip_path.apply_affine(transform.cast().into());
        let blend_mode = peniko::Compose::Clear;
        self.ctx.push_layer(
            Some(&clip_path.to_path(0.1)),
            Some(blend_mode.into()),
            None,
            None,
        );
        self.ctx.pop_layer();
    }

    fn copy_surface(
        &mut self,
        surface: Self::SourceSurface,
        source: Rect<i32>,
        destination: Point2D<i32>,
    ) {
        self.ensure_drawing();
        let destination: kurbo::Point = destination.cast::<f64>().into();
        let rect = kurbo::Rect::from_origin_size(destination, source.size.cast());
        self.ctx.set_transform(kurbo::Affine::IDENTITY);
        self.ignore_clips(|self_| {
            // Clipped blending does not work correctly:
            // https://github.com/linebender/vello/issues/1119
            // self_.push_layer(Some(rect.to_path(0.1)), Some(peniko::Compose::Copy.into()), None, None);

            self_.ctx.set_paint(vello_cpu::Image {
                source: vello_cpu::ImageSource::Pixmap(surface),
                x_extend: peniko::Extend::Pad,
                y_extend: peniko::Extend::Pad,
                quality: peniko::ImageQuality::Low,
            });
            self_.ctx.fill_rect(&rect);

            // self_.ctx.pop_layer();
        });
    }

    fn create_similar_draw_target(&self, size: &Size2D<i32>) -> Self {
        Self::new(size.cast())
    }

    fn draw_surface(
        &mut self,
        mut surface: Self::SourceSurface,
        dest: Rect<f64>,
        source: Rect<f64>,
        filter: Filter,
        composition_options: CompositionOptions,
        transform: Transform2D<f64>,
    ) {
        self.ensure_drawing();
        let scale_up = dest.size.width > source.size.width || dest.size.height > source.size.height;
        if composition_options.alpha != 1.0 {
            Arc::get_mut(&mut surface)
                .expect("surface should be owned")
                .multiply_alpha((composition_options.alpha * 255.0) as u8);
        }
        self.with_composition(composition_options.composition_operation, move |self_| {
            self_.ctx.set_transform(transform.cast().into());
            self_.ctx.set_paint(vello_cpu::Image {
                source: vello_cpu::ImageSource::Pixmap(surface),
                x_extend: peniko::Extend::Pad,
                y_extend: peniko::Extend::Pad,
                // we should only do bicubic when scaling up
                quality: if scale_up {
                    filter.convert()
                } else {
                    peniko::ImageQuality::Low
                },
            });
            self_.ctx.set_paint_transform(
                kurbo::Affine::translate((dest.origin.x, dest.origin.y)).pre_scale_non_uniform(
                    dest.size.width / source.size.width,
                    dest.size.height / source.size.height,
                ),
            );
            self_.ctx.fill_rect(&dest.into());
            self_.ctx.reset_paint_transform();
        })
    }

    fn draw_surface_with_shadow(
        &self,
        _surface: Self::SourceSurface,
        _dest: &Point2D<f32>,
        _shadow_options: ShadowOptions,
        _composition_options: CompositionOptions,
    ) {
        log::warn!("no support for drawing shadows");
        /*
        We will need to do some changes to support drawing shadows with vello, as current abstraction is made for azure.
        In vello we do not need new draw target (we will use layers) and we need to pass whole rect.
        offsets will be applied to rect directly. shadow blur will be passed directly to let backend do transforms.
        */
        // self_.scene.draw_blurred_rounded_rect(self_.transform, rect, color, 0.0, sigma);
    }

    fn fill(
        &mut self,
        path: &Path,
        fill_rule: FillRule,
        style: FillOrStrokeStyle,
        composition_options: CompositionOptions,
        transform: Transform2D<f64>,
    ) {
        self.ensure_drawing();
        self.with_composition(composition_options.composition_operation, |self_| {
            self_.ctx.set_transform(transform.cast().into());
            self_.ctx.set_fill_rule(fill_rule.convert());
            self_.ctx.set_paint(paint(style, composition_options.alpha));
            self_.ctx.fill_path(&path.0);
        });
        self.ctx.set_fill_rule(peniko::Fill::NonZero);
    }

    fn fill_text(
        &mut self,
        text_runs: Vec<TextRun>,
        style: FillOrStrokeStyle,
        composition_options: CompositionOptions,
        transform: Transform2D<f64>,
    ) {
        self.ensure_drawing();
        self.ctx.set_paint(paint(style, composition_options.alpha));
        self.ctx.set_transform(transform.cast().into());
        self.with_composition(composition_options.composition_operation, |self_| {
            for text_run in text_runs.iter() {
                SHARED_FONT_CACHE.with(|font_cache| {
                    let identifier = &text_run.font.identifier;
                    if !font_cache.borrow().contains_key(identifier) {
                        let Some(font_data_and_index) = text_run.font.font_data_and_index() else {
                            return;
                        };
                        let font = font_data_and_index.convert();
                        font_cache.borrow_mut().insert(identifier.clone(), font);
                    }

                    let font_cache = font_cache.borrow();
                    let Some(font) = font_cache.get(identifier) else {
                        return;
                    };
                    self_
                        .ctx
                        .glyph_run(font)
                        .font_size(text_run.pt_size)
                        .fill_glyphs(text_run.glyphs_and_positions.iter().map(
                            |glyph_and_position| vello_cpu::Glyph {
                                id: glyph_and_position.id,
                                x: glyph_and_position.point.x,
                                y: glyph_and_position.point.y,
                            },
                        ));
                });
            }
        })
    }

    fn fill_rect(
        &mut self,
        rect: &Rect<f32>,
        style: FillOrStrokeStyle,
        composition_options: CompositionOptions,
        transform: Transform2D<f64>,
    ) {
        self.ensure_drawing();
        self.with_composition(composition_options.composition_operation, |self_| {
            self_.ctx.set_transform(transform.cast().into());
            self_.ctx.set_paint(paint(style, composition_options.alpha));
            self_.ctx.fill_rect(&rect.cast().into());
        })
    }

    fn get_size(&self) -> Size2D<i32> {
        self.size().cast()
    }

    fn pop_clip(&mut self) {
        if self.clips.pop().is_some() {
            self.ctx.pop_layer();
        }
    }

    fn push_clip(&mut self, path: &Path, fill_rule: FillRule, transform: Transform2D<f64>) {
        self.ctx.set_transform(transform.cast().into());
        let mut path = path.clone();
        path.transform(transform.cast());
        self.ctx.set_fill_rule(fill_rule.convert());
        self.ctx.push_clip_layer(&path.0);
        self.clips.push(path);
        self.ctx.set_fill_rule(peniko::Fill::NonZero);
    }

    fn push_clip_rect(&mut self, rect: &Rect<i32>) {
        let mut path = Path::new();
        let rect = rect.cast();
        path.rect(
            rect.origin.x,
            rect.origin.y,
            rect.size.width,
            rect.size.height,
        );
        self.push_clip(&path, FillRule::Nonzero, Transform2D::identity());
    }

    fn stroke(
        &mut self,
        path: &Path,
        style: FillOrStrokeStyle,
        line_options: LineOptions,
        composition_options: CompositionOptions,
        transform: Transform2D<f64>,
    ) {
        self.ensure_drawing();
        self.with_composition(composition_options.composition_operation, |self_| {
            self_.ctx.set_transform(transform.cast().into());
            self_.ctx.set_paint(paint(style, composition_options.alpha));
            self_.ctx.set_stroke(line_options.convert());
            self_.ctx.stroke_path(&path.0);
        })
    }

    fn stroke_text(
        &mut self,
        text_runs: Vec<TextRun>,
        style: FillOrStrokeStyle,
        line_options: LineOptions,
        composition_options: CompositionOptions,
        transform: Transform2D<f64>,
    ) {
        self.ensure_drawing();
        self.ctx.set_paint(paint(style, composition_options.alpha));
        self.ctx.set_stroke(line_options.convert());
        self.ctx.set_transform(transform.cast().into());
        self.with_composition(composition_options.composition_operation, |self_| {
            for text_run in text_runs.iter() {
                SHARED_FONT_CACHE.with(|font_cache| {
                    let identifier = &text_run.font.identifier;
                    if !font_cache.borrow().contains_key(identifier) {
                        let Some(font_data_and_index) = text_run.font.font_data_and_index() else {
                            return;
                        };
                        let font = font_data_and_index.convert();
                        font_cache.borrow_mut().insert(identifier.clone(), font);
                    }

                    let font_cache = font_cache.borrow();
                    let Some(font) = font_cache.get(identifier) else {
                        return;
                    };
                    self_
                        .ctx
                        .glyph_run(font)
                        .font_size(text_run.pt_size)
                        .stroke_glyphs(text_run.glyphs_and_positions.iter().map(
                            |glyph_and_position| vello_cpu::Glyph {
                                id: glyph_and_position.id,
                                x: glyph_and_position.point.x,
                                y: glyph_and_position.point.y,
                            },
                        ));
                });
            }
        })
    }

    fn stroke_rect(
        &mut self,
        rect: &Rect<f32>,
        style: FillOrStrokeStyle,
        line_options: LineOptions,
        composition_options: CompositionOptions,
        transform: Transform2D<f64>,
    ) {
        self.ensure_drawing();
        self.with_composition(composition_options.composition_operation, |self_| {
            self_.ctx.set_transform(transform.cast().into());
            self_.ctx.set_paint(paint(style, composition_options.alpha));
            self_.ctx.set_stroke(line_options.convert());
            self_.ctx.stroke_rect(&rect.cast().into());
        })
    }

    fn image_descriptor_and_serializable_data(
        &mut self,
    ) -> (ImageDescriptor, SerializableImageData) {
        let image_desc = ImageDescriptor {
            format: webrender_api::ImageFormat::RGBA8,
            size: self.size().cast().cast_unit(),
            stride: None,
            offset: 0,
            flags: ImageDescriptorFlags::empty(),
        };
        let data = SerializableImageData::Raw(IpcSharedMemory::from_bytes(self.pixmap()));
        (image_desc, data)
    }

    fn snapshot(&mut self) -> pixels::Snapshot {
        Snapshot::from_vec(
            self.size().cast(),
            SnapshotPixelFormat::RGBA,
            SnapshotAlphaMode::Transparent {
                premultiplied: true,
            },
            self.pixmap().to_vec(),
        )
    }

    fn surface(&mut self) -> Self::SourceSurface {
        self.pixmap(); // sync pixmap
        Arc::new(vello_cpu::Pixmap::from_parts(
            self.pixmap.clone().take(),
            self.pixmap.width(),
            self.pixmap.height(),
        ))
    }

    fn create_source_surface_from_data(&self, data: Snapshot) -> Option<Self::SourceSurface> {
        Some(snapshot_as_pixmap(data))
    }
}

fn snapshot_as_pixmap(data: Snapshot) -> Arc<vello_cpu::Pixmap> {
    let size = data.size().cast();
    let (data, _, _) = data.to_vec(
        Some(SnapshotAlphaMode::Transparent {
            premultiplied: true,
        }),
        Some(SnapshotPixelFormat::RGBA),
    );
    Arc::new(vello_cpu::Pixmap::from_parts(
        bytemuck::cast_vec(data),
        size.width,
        size.height,
    ))
}

impl Convert<vello_cpu::PaintType> for FillOrStrokeStyle {
    fn convert(self) -> vello_cpu::PaintType {
        use canvas_traits::canvas::FillOrStrokeStyle::*;
        match self {
            Color(absolute_color) => vello_cpu::PaintType::Solid(absolute_color.convert()),
            LinearGradient(style) => {
                let start = kurbo::Point::new(style.x0, style.y0);
                let end = kurbo::Point::new(style.x1, style.y1);
                let mut gradient = peniko::Gradient::new_linear(start, end);
                gradient.stops = style.stops.convert();
                vello_cpu::PaintType::Gradient(gradient)
            },
            RadialGradient(style) => {
                let center1 = kurbo::Point::new(style.x0, style.y0);
                let center2 = kurbo::Point::new(style.x1, style.y1);
                let mut gradient = peniko::Gradient::new_two_point_radial(
                    center1,
                    style.r0 as f32,
                    center2,
                    style.r1 as f32,
                );
                gradient.stops = style.stops.convert();
                vello_cpu::PaintType::Gradient(gradient)
            },
            Surface(surface_style) => {
                let pixmap = snapshot_as_pixmap(surface_style.surface_data.to_owned());
                vello_cpu::PaintType::Image(vello_cpu::Image {
                    source: vello_cpu::ImageSource::Pixmap(pixmap),
                    x_extend: if surface_style.repeat_x {
                        peniko::Extend::Repeat
                    } else {
                        peniko::Extend::Pad
                    },
                    y_extend: if surface_style.repeat_y {
                        peniko::Extend::Repeat
                    } else {
                        peniko::Extend::Pad
                    },
                    quality: peniko::ImageQuality::Low,
                })
            },
        }
    }
}

fn paint(style: FillOrStrokeStyle, alpha: f64) -> vello_cpu::PaintType {
    assert!((0.0..=1.0).contains(&alpha));
    let paint = style.convert();
    if alpha == 1.0 {
        paint
    } else {
        match paint {
            vello_cpu::PaintType::Solid(alpha_color) => {
                vello_cpu::PaintType::Solid(alpha_color.multiply_alpha(alpha as f32))
            },
            vello_cpu::PaintType::Gradient(gradient) => {
                vello_cpu::PaintType::Gradient(gradient.multiply_alpha(alpha as f32))
            },
            vello_cpu::PaintType::Image(mut image) => {
                match &mut image.source {
                    vello_cpu::ImageSource::Pixmap(pixmap) => Arc::get_mut(pixmap)
                        .expect("pixmap should not be shared with anyone at this point")
                        .multiply_alpha((alpha * 255.0) as u8),
                    vello_cpu::ImageSource::OpaqueId(_) => unimplemented!(),
                };
                vello_cpu::PaintType::Image(image)
            },
        }
    }
}