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canvas: Add OffscreenCanvas 'convertToBlob' method (#37786)

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Follow the HTML speficication and add missing 'convertToBlob' method
to OffscreenCanvas interface.

https://html.spec.whatwg.org/multipage/#dom-offscreencanvas-converttoblob

Testing: Improvements in the following tests
-
html/canvas/offscreen/manual/convert-to-blob/offscreencanvas.convert.to.blob*
-
html/canvas/offscreen/manual/wide-gamut-canvas/2d.color.space.p3.convertToBlobp3.canvas.html

Fixes: #24272

Signed-off-by: Andrei Volykhin <andrei.volykhin@gmail.com>
This commit is contained in:
Andrei Volykhin 2025-07-04 09:58:12 +03:00 • committed by GitHub
parent 3ba5b89ef2
commit 6ba54e4d79
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GPG key ID: B5690EEEBB952194
11 changed files with 187 additions and 187 deletions
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123
components/script/dom/htmlcanvaselement.rs
View file

@ -13,16 +13,12 @@ use constellation_traits::ScriptToConstellationMessage;
use dom_struct::dom_struct;
use euclid::default::Size2D;
use html5ever::{LocalName, Prefix, local_name, ns};
use image::codecs::jpeg::JpegEncoder;
use image::codecs::png::PngEncoder;
use image::codecs::webp::WebPEncoder;
use image::{ColorType, ImageEncoder, ImageError};
#[cfg(feature = "webgpu")]
use ipc_channel::ipc::{self as ipcchan};
use js::error::throw_type_error;
use js::rust::{HandleObject, HandleValue};
use layout_api::HTMLCanvasData;
use pixels::{Snapshot, SnapshotAlphaMode, SnapshotPixelFormat};
use pixels::{EncodedImageType, Snapshot};
use script_bindings::weakref::WeakRef;
use servo_media::streams::MediaStreamType;
use servo_media::streams::registry::MediaStreamId;
@ -70,41 +66,6 @@ use crate::script_runtime::{CanGc, JSContext};
const DEFAULT_WIDTH: u32 = 300;
const DEFAULT_HEIGHT: u32 = 150;
#[derive(PartialEq)]
enum EncodedImageType {
Png,
Jpeg,
Webp,
}
impl From<DOMString> for EncodedImageType {
// From: https://html.spec.whatwg.org/multipage/#serialising-bitmaps-to-a-file
// User agents must support PNG ("image/png"). User agents may support other types.
// If the user agent does not support the requested type, then it must create the file using the PNG format.
// Anything different than image/jpeg or image/webp is thus treated as PNG.
fn from(mime_type: DOMString) -> Self {
let mime = mime_type.to_string().to_lowercase();
if mime == "image/jpeg" {
Self::Jpeg
} else if mime == "image/webp" {
Self::Webp
} else {
Self::Png
}
}
}
impl EncodedImageType {
fn as_mime_type(&self) -> String {
match self {
Self::Png => "image/png",
Self::Jpeg => "image/jpeg",
Self::Webp => "image/webp",
}
.to_owned()
}
}
/// <https://html.spec.whatwg.org/multipage/#htmlcanvaselement>
#[dom_struct]
pub(crate) struct HTMLCanvasElement {
@ -385,68 +346,6 @@ impl HTMLCanvasElement {
None
}
}
fn encode_for_mime_type<W: std::io::Write>(
&self,
image_type: &EncodedImageType,
quality: Option<f64>,
mut snapshot: Snapshot,
encoder: &mut W,
) -> Result<(), ImageError> {
// We can't use self.Width() or self.Height() here, since the size of the canvas
// may have changed since the snapshot was created. Truncating the dimensions to a
// u32 can't panic, since the data comes from a canvas which is always smaller than
// u32::MAX.
let width = snapshot.size().width;
let height = snapshot.size().height;
let (canvas_data, _, _) = snapshot.as_bytes(
if *image_type == EncodedImageType::Jpeg {
Some(SnapshotAlphaMode::AsOpaque {
premultiplied: true,
})
} else {
Some(SnapshotAlphaMode::Transparent {
premultiplied: false,
})
},
Some(SnapshotPixelFormat::RGBA),
);
match image_type {
EncodedImageType::Png => {
// FIXME(nox): https://github.com/image-rs/image-png/issues/86
// FIXME(nox): https://github.com/image-rs/image-png/issues/87
PngEncoder::new(encoder).write_image(canvas_data, width, height, ColorType::Rgba8)
},
EncodedImageType::Jpeg => {
let jpeg_encoder = if let Some(quality) = quality {
// The specification allows quality to be in [0.0..1.0] but the JPEG encoder
// expects it to be in [1..100]
if (0.0..=1.0).contains(&quality) {
JpegEncoder::new_with_quality(
encoder,
(quality * 100.0).round().clamp(1.0, 100.0) as u8,
)
} else {
JpegEncoder::new(encoder)
}
} else {
JpegEncoder::new(encoder)
};
jpeg_encoder.write_image(canvas_data, width, height, ColorType::Rgba8)
},
EncodedImageType::Webp => {
// No quality support because of https://github.com/image-rs/image/issues/1984
WebPEncoder::new_lossless(encoder).write_image(
canvas_data,
width,
height,
ColorType::Rgba8,
)
},
}
}
}
impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
@ -548,11 +447,11 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
// Step 3: Let file be a serialization of this canvas element's bitmap as a file,
// passing type and quality if given.
let Some(snapshot) = self.get_image_data() else {
let Some(mut snapshot) = self.get_image_data() else {
return Ok(USVString("data:,".into()));
};
let image_type = EncodedImageType::from(mime_type);
let image_type = EncodedImageType::from(mime_type.to_string());
let mut url = format!("data:{};base64,", image_type.as_mime_type());
@ -561,13 +460,8 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
&base64::engine::general_purpose::STANDARD,
);
if self
.encode_for_mime_type(
&image_type,
Self::maybe_quality(quality),
snapshot,
&mut encoder,
)
if snapshot
.encode_for_mime_type(&image_type, Self::maybe_quality(quality), &mut encoder)
.is_err()
{
// Step 4. If file is null, then return "data:,".
@ -612,7 +506,8 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
.borrow_mut()
.insert(callback_id, callback);
let quality = Self::maybe_quality(quality);
let image_type = EncodedImageType::from(mime_type);
let image_type = EncodedImageType::from(mime_type.to_string());
self.global()
.task_manager()
.canvas_blob_task_source()
@ -622,7 +517,7 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
return error!("Expected blob callback, but found none!");
};
let Some(snapshot) = result else {
let Some(mut snapshot) = result else {
let _ = callback.Call__(None, ExceptionHandling::Report, CanGc::note());
return;
};
@ -634,7 +529,7 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
let mut encoded: Vec<u8> = vec![];
let blob_impl;
let blob;
let result = match this.encode_for_mime_type(&image_type, quality, snapshot, &mut encoded) {
let result = match snapshot.encode_for_mime_type(&image_type, quality, &mut encoded) {
Ok(..) => {
// Step 4.2.1: If result is non-null, then set result to a new Blob
// object, created in the relevant realm of this canvas element,

78
components/script/dom/offscreencanvas.rs
View file

@ -3,26 +3,33 @@
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
use std::cell::Cell;
use std::rc::Rc;
use constellation_traits::BlobImpl;
use dom_struct::dom_struct;
use euclid::default::Size2D;
use js::rust::{HandleObject, HandleValue};
use pixels::Snapshot;
use pixels::{EncodedImageType, Snapshot};
use script_bindings::weakref::WeakRef;
use crate::canvas_context::{CanvasContext, OffscreenRenderingContext};
use crate::dom::bindings::cell::{DomRefCell, Ref};
use crate::dom::bindings::codegen::Bindings::OffscreenCanvasBinding::{
OffscreenCanvasMethods, OffscreenRenderingContext as RootedOffscreenRenderingContext,
ImageEncodeOptions, OffscreenCanvasMethods,
OffscreenRenderingContext as RootedOffscreenRenderingContext,
};
use crate::dom::bindings::error::{Error, Fallible};
use crate::dom::bindings::refcounted::{Trusted, TrustedPromise};
use crate::dom::bindings::reflector::{DomGlobal, reflect_dom_object_with_proto};
use crate::dom::bindings::root::{Dom, DomRoot};
use crate::dom::bindings::str::DOMString;
use crate::dom::blob::Blob;
use crate::dom::eventtarget::EventTarget;
use crate::dom::globalscope::GlobalScope;
use crate::dom::htmlcanvaselement::HTMLCanvasElement;
use crate::dom::offscreencanvasrenderingcontext2d::OffscreenCanvasRenderingContext2D;
use crate::dom::promise::Promise;
use crate::realms::{AlreadyInRealm, InRealm};
use crate::script_runtime::{CanGc, JSContext};
/// <https://html.spec.whatwg.org/multipage/#offscreencanvas>
@ -206,4 +213,71 @@ impl OffscreenCanvasMethods<crate::DomTypeHolder> for OffscreenCanvas {
canvas.set_natural_height(value as _, can_gc)
}
}
/// <https://html.spec.whatwg.org/multipage/#dom-offscreencanvas-converttoblob>
fn ConvertToBlob(&self, options: &ImageEncodeOptions, can_gc: CanGc) -> Rc<Promise> {
// Step 5. Let result be a new promise object.
let in_realm_proof = AlreadyInRealm::assert::<crate::DomTypeHolder>();
let promise = Promise::new_in_current_realm(InRealm::Already(&in_realm_proof), can_gc);
// Step 2. If this's context mode is 2d and the rendering context's
// output bitmap's origin-clean flag is set to false, then return a
// promise rejected with a "SecurityError" DOMException.
if !self.origin_is_clean() {
promise.reject_error(Error::Security, can_gc);
return promise;
}
// Step 3. If this's bitmap has no pixels (i.e., either its horizontal
// dimension or its vertical dimension is zero), then return a promise
// rejected with an "IndexSizeError" DOMException.
if self.Width() == 0 || self.Height() == 0 {
promise.reject_error(Error::IndexSize, can_gc);
return promise;
}
// Step 4. Let bitmap be a copy of this's bitmap.
let Some(mut snapshot) = self.get_image_data() else {
promise.reject_error(Error::InvalidState, can_gc);
return promise;
};
// Step 7. Run these steps in parallel:
// Step 7.1. Let file be a serialization of bitmap as a file, with
// options's type and quality if present.
// Step 7.2. Queue a global task on the canvas blob serialization task
// source given global to run these steps:
let trusted_this = Trusted::new(self);
let trusted_promise = TrustedPromise::new(promise.clone());
let image_type = EncodedImageType::from(options.type_.to_string());
let quality = options.quality;
self.global()
.task_manager()
.canvas_blob_task_source()
.queue(task!(convert_to_blob: move || {
let this = trusted_this.root();
let promise = trusted_promise.root();
let mut encoded: Vec<u8> = vec![];
if snapshot.encode_for_mime_type(&image_type, quality, &mut encoded).is_err() {
// Step 7.2.1. If file is null, then reject result with an
// "EncodingError" DOMException.
promise.reject_error(Error::Encoding, CanGc::note());
return;
};
// Step 7.2.2. Otherwise, resolve result with a new Blob object,
// created in global's relevant realm, representing file.
let blob_impl = BlobImpl::new_from_bytes(encoded, image_type.as_mime_type());
let blob = Blob::new(&this.global(), blob_impl, CanGc::note());
promise.resolve_native(&blob, CanGc::note());
}));
// Step 8. Return result.
promise
}
}