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Introduce snapshot concept of canvas (#36119)

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Each canvas context returns snapshot instead of just raw bytes. This
allows as to hold off conversions (BGRA <-> RGBA, (un)premultiply) to
when/if they are actually needed. For example when loading snapshot into
webgl we can load both RGBA and BGRA so no conversion is really needed.

Currently whole thing is designed to be able to be extend on
https://github.com/servo/ipc-channel/pull/356, to make less copies.
Hence some commented out code.


Fixes #35759
There are tests for these changes in WPT

---------

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>
This commit is contained in:
sagudev 2025-04-23 09:32:47 +02:00 • committed by GitHub
parent b6967fc4c8
commit 73b778e67f
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37 changed files with 724 additions and 251 deletions
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78
components/script/dom/htmlcanvaselement.rs
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@ -17,7 +17,6 @@ use image::codecs::jpeg::JpegEncoder;
use image::codecs::png::PngEncoder;
use image::codecs::webp::WebPEncoder;
use image::{ColorType, ImageEncoder};
use ipc_channel::ipc::IpcSharedMemory;
#[cfg(feature = "webgpu")]
use ipc_channel::ipc::{self as ipcchan};
use js::error::throw_type_error;
@ -25,6 +24,7 @@ use js::rust::{HandleObject, HandleValue};
use script_layout_interface::{HTMLCanvasData, HTMLCanvasDataSource};
use servo_media::streams::MediaStreamType;
use servo_media::streams::registry::MediaStreamId;
use snapshot::Snapshot;
use style::attr::AttrValue;
use crate::canvas_context::CanvasContext as _;
@ -69,6 +69,7 @@ use crate::script_runtime::{CanGc, JSContext};
const DEFAULT_WIDTH: u32 = 300;
const DEFAULT_HEIGHT: u32 = 150;
#[derive(PartialEq)]
enum EncodedImageType {
Png,
Jpeg,
@ -375,42 +376,21 @@ impl HTMLCanvasElement {
self.Height() != 0 && self.Width() != 0
}
pub(crate) fn fetch_all_data(&self) -> Option<(Option<IpcSharedMemory>, Size2D<u32>)> {
let size = self.get_size();
if size.width == 0 || size.height == 0 {
return None;
}
let data = match self.context.borrow().as_ref() {
Some(CanvasContext::Context2d(context)) => context.get_image_data_as_shared_memory(),
Some(CanvasContext::WebGL(_context)) => {
// TODO: add a method in WebGLRenderingContext to get the pixels.
return None;
},
Some(CanvasContext::WebGL2(_context)) => {
// TODO: add a method in WebGL2RenderingContext to get the pixels.
return None;
},
pub(crate) fn get_image_data(&self) -> Option<Snapshot> {
match self.context.borrow().as_ref() {
Some(CanvasContext::Context2d(context)) => context.get_image_data(),
Some(CanvasContext::WebGL(context)) => context.get_image_data(),
Some(CanvasContext::WebGL2(context)) => context.get_image_data(),
#[cfg(feature = "webgpu")]
Some(CanvasContext::WebGPU(context)) => context.get_image_data_as_shared_memory(),
Some(CanvasContext::Placeholder(context)) => return context.fetch_all_data(),
None => None,
};
Some((data, size))
}
fn get_content(&self) -> Option<Vec<u8>> {
match *self.context.borrow() {
Some(CanvasContext::Context2d(ref context)) => context.get_image_data(),
Some(CanvasContext::WebGL(ref context)) => context.get_image_data(),
Some(CanvasContext::WebGL2(ref context)) => context.get_image_data(),
#[cfg(feature = "webgpu")]
Some(CanvasContext::WebGPU(ref context)) => context.get_image_data(),
Some(CanvasContext::Placeholder(_)) | None => {
// Each pixel is fully-transparent black.
Some(vec![0; (self.Width() * self.Height() * 4) as usize])
Some(CanvasContext::WebGPU(context)) => context.get_image_data(),
Some(CanvasContext::Placeholder(context)) => context.get_image_data(),
None => {
let size = self.get_size();
if size.width == 0 || size.height == 0 {
None
} else {
Some(Snapshot::cleared(size.cast()))
}
},
}
}
@ -560,11 +540,23 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
}
// Step 3.
let Some(file) = self.get_content() else {
let Some(mut snapshot) = self.get_image_data() else {
return Ok(USVString("data:,".into()));
};
let image_type = EncodedImageType::from(mime_type);
snapshot.transform(
if image_type == EncodedImageType::Jpeg {
snapshot::AlphaMode::AsOpaque {
premultiplied: true,
}
} else {
snapshot::AlphaMode::Transparent {
premultiplied: false,
}
},
snapshot::PixelFormat::RGBA,
);
let mut url = format!("data:{};base64,", image_type.as_mime_type());
let mut encoder = base64::write::EncoderStringWriter::from_consumer(
@ -575,7 +567,7 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
self.encode_for_mime_type(
&image_type,
Self::maybe_quality(quality),
&file,
snapshot.data(),
&mut encoder,
);
encoder.into_inner();
@ -604,7 +596,7 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
let result = if self.Width() == 0 || self.Height() == 0 {
None
} else {
self.get_content()
self.get_image_data()
};
let this = Trusted::new(self);
@ -625,13 +617,17 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
return error!("Expected blob callback, but found none!");
};
if let Some(bytes) = result {
if let Some(mut snapshot) = result {
snapshot.transform(
snapshot::AlphaMode::Transparent{ premultiplied: false },
snapshot::PixelFormat::RGBA
);
// Step 4.1
// If result is non-null, then set result to a serialization of result as a file with
// type and quality if given.
let mut encoded: Vec<u8> = vec![];
this.encode_for_mime_type(&image_type, quality, &bytes, &mut encoded);
this.encode_for_mime_type(&image_type, quality, snapshot.data(), &mut encoded);
let blob_impl = BlobImpl::new_from_bytes(encoded, image_type.as_mime_type());
// Step 4.2.1 & 4.2.2
// Set result to a new Blob object, created in the relevant realm of this canvas element