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Why do you think that polyfills can't implement progressive decoding? It's simply a matter of using <canvas> for progressive rendering.

by Sephr 4y ago

lifthrasiir 4y ago
Canvas has to retain all pixels unconditionally, unlike native images that can be unloaded from memory as needed. It is technically possible to implement all other features (using service workers or CSS Houdini), but tons of limitations apply and can easily outstrip supposed benefits.
- supermatt 4y ago
  Can't you just read the stream and emit the images(s) as they get downloaded to be rendered in a canvas - exactly as a native implementation would do?
  - niutech 4y ago
    This is what I did with JXL.js Multithread (https://github.com/niutech/jxl.js#multithread-version https://github.com/niutech/jxl.js#multithread-version) - but instead of <canvas> I am pushing the blob to the <img>.
  - lifthrasiir 4y ago
    My comment was apparently too concise to give you a sense of complications. I can think of those concrete problems: - Rendering images from a different origin without CORS. This is a fundamental limitation of any JS or WebAssembly solution and can't be fixed. Thankfully this use case is relatively rare. - Not all approaches can provide a seamless upgrade. For example if you replace all `<img src="foo.jxl">` with a canvas DOM will be changed and anything expecting the element to be HTMLImageElement will break. Likewise, CSS Painting API [1] (a relevant part of CSS Houdini) requires you to explicitly write `paint(foo)` everywhere. The only seamless solution will be therefore a service worker, but it can't introduce any new image format; it can only convert to natively supported formats. And browsers currently don't have a "raw" image format for this purpose. JXL.js [2] for example had to use JPEG as a delivery format because other formats were too slow, as I've been told. - It is very hard to check if a certain image is visible or not, and react accordingly. This is what I intended to imply by saying that canvas has to unconditionally retain all pixels, because if implementations can't decide if it's safe to unload images, they can't do so and memory will contain invisible images in the form of canvases. Browsers do have a ground truth and so can safely unload currently invisible images from memory when the memory pressure is high. [1] https://developer.mozilla.org/en-US/docs/Web/API/CSS_Painting_API https://developer.mozilla.org/en-US/docs/Web/API/CSS_Paintin... [2] https://github.com/niutech/jxl.js https://github.com/niutech/jxl.js
    - Sephr 4y ago
      > Not all approaches can provide a seamless upgrade. For example if you replace all `<img src="foo.jxl">` with a canvas DOM will be changed and anything expecting the element to be HTMLImageElement will break. Likewise, CSS Painting API [1] (a relevant part of CSS Houdini) requires you to explicitly write `paint(foo)` everywhere. The only seamless solution will be therefore a service worker, but it can't introduce any new image format; it can only convert to natively supported formats. And browsers currently don't have a "raw" image format for this purpose. JXL.js [2] for example had to use JPEG as a delivery format because other formats were too slow, as I've been told. You can get around many these compatibility issues by creating a custom element that inherits from HTMLImageElement. This provides API compatibility. For CSS compatibility, the elements you would replace in a MutationObserver would be the same tag name but a different namespace for CSS compatibility. For the CSS compatibility trick, see https://eligrey.com/demos/hotlink.js/ https://eligrey.com/demos/hotlink.js/ which replaces images with CSS-compatible (not HTMLImageElement-compatible) iframes. > - It is very hard to check if a certain image is visible or not, and react accordingly. You can use Element.checkVisibility()¹ and the contentvisibilityautostatechanged event²𝄒³ to do this. Browser support is currently limited to Chromium-based browsers. 1. https://drafts.csswg.org/cssom-view/#dom-element-checkvisibility https://drafts.csswg.org/cssom-view/#dom-element-checkvisibi... 2. https://github.com/vmpstr/web-proposals/blob/main/explainers/cv-auto-event.md#example https://github.com/vmpstr/web-proposals/blob/main/explainers... 3. https://caniuse.com/mdn-api_element_contentvisibilityautostatechanged_event https://caniuse.com/mdn-api_element_contentvisibilityautosta...
      - lifthrasiir 4y ago
        Thank you for pointing out contentvisibilityautostatechanged, I was aware of `content-visibility` but didn't know that it has an associated event. I'm less sure about CSS compatibility, hotlink.js for example used an iframe which opens a whole can of worms.
    - niutech 4y ago
      I've just added a config parameter to JXL.js for choosing the target image type: JPG/PNG/WebP. Keep in mind that PNGs can take a lot memory!

Why do you think that polyfills can't implement progressive decoding? It's simply a matter of using <canvas> for progressive rendering.

by Sephr 4y ago

Why do you think that polyfills can't implement progressive decoding? It's simply a matter of using <canvas> for progressive rendering.

lifthrasiir 4y ago

Canvas has to retain all pixels unconditionally, unlike native images that can be unloaded from memory as needed. It is technically possible to implement all other features (using service workers or CSS Houdini), but tons of limitations apply and can easily outstrip supposed benefits.

supermatt 4y ago
Can't you just read the stream and emit the images(s) as they get downloaded to be rendered in a canvas - exactly as a native implementation would do?
- niutech 4y ago
  This is what I did with JXL.js Multithread (https://github.com/niutech/jxl.js#multithread-version https://github.com/niutech/jxl.js#multithread-version) - but instead of <canvas> I am pushing the blob to the <img>.
- lifthrasiir 4y ago
  My comment was apparently too concise to give you a sense of complications. I can think of those concrete problems: - Rendering images from a different origin without CORS. This is a fundamental limitation of any JS or WebAssembly solution and can't be fixed. Thankfully this use case is relatively rare. - Not all approaches can provide a seamless upgrade. For example if you replace all `<img src="foo.jxl">` with a canvas DOM will be changed and anything expecting the element to be HTMLImageElement will break. Likewise, CSS Painting API [1] (a relevant part of CSS Houdini) requires you to explicitly write `paint(foo)` everywhere. The only seamless solution will be therefore a service worker, but it can't introduce any new image format; it can only convert to natively supported formats. And browsers currently don't have a "raw" image format for this purpose. JXL.js [2] for example had to use JPEG as a delivery format because other formats were too slow, as I've been told. - It is very hard to check if a certain image is visible or not, and react accordingly. This is what I intended to imply by saying that canvas has to unconditionally retain all pixels, because if implementations can't decide if it's safe to unload images, they can't do so and memory will contain invisible images in the form of canvases. Browsers do have a ground truth and so can safely unload currently invisible images from memory when the memory pressure is high. [1] https://developer.mozilla.org/en-US/docs/Web/API/CSS_Painting_API https://developer.mozilla.org/en-US/docs/Web/API/CSS_Paintin... [2] https://github.com/niutech/jxl.js https://github.com/niutech/jxl.js
  - Sephr 4y ago
    > Not all approaches can provide a seamless upgrade. For example if you replace all `<img src="foo.jxl">` with a canvas DOM will be changed and anything expecting the element to be HTMLImageElement will break. Likewise, CSS Painting API [1] (a relevant part of CSS Houdini) requires you to explicitly write `paint(foo)` everywhere. The only seamless solution will be therefore a service worker, but it can't introduce any new image format; it can only convert to natively supported formats. And browsers currently don't have a "raw" image format for this purpose. JXL.js [2] for example had to use JPEG as a delivery format because other formats were too slow, as I've been told. You can get around many these compatibility issues by creating a custom element that inherits from HTMLImageElement. This provides API compatibility. For CSS compatibility, the elements you would replace in a MutationObserver would be the same tag name but a different namespace for CSS compatibility. For the CSS compatibility trick, see https://eligrey.com/demos/hotlink.js/ https://eligrey.com/demos/hotlink.js/ which replaces images with CSS-compatible (not HTMLImageElement-compatible) iframes. > - It is very hard to check if a certain image is visible or not, and react accordingly. You can use Element.checkVisibility()¹ and the contentvisibilityautostatechanged event²𝄒³ to do this. Browser support is currently limited to Chromium-based browsers. 1. https://drafts.csswg.org/cssom-view/#dom-element-checkvisibility https://drafts.csswg.org/cssom-view/#dom-element-checkvisibi... 2. https://github.com/vmpstr/web-proposals/blob/main/explainers/cv-auto-event.md#example https://github.com/vmpstr/web-proposals/blob/main/explainers... 3. https://caniuse.com/mdn-api_element_contentvisibilityautostatechanged_event https://caniuse.com/mdn-api_element_contentvisibilityautosta...
    - lifthrasiir 4y ago
      Thank you for pointing out contentvisibilityautostatechanged, I was aware of `content-visibility` but didn't know that it has an associated event. I'm less sure about CSS compatibility, hotlink.js for example used an iframe which opens a whole can of worms.
  - niutech 4y ago
    I've just added a config parameter to JXL.js for choosing the target image type: JPG/PNG/WebP. Keep in mind that PNGs can take a lot memory!