Start decoding images immediately

[SelfishPig]

After a recent commit, images are set to decode asynchronously. However, decoding is not initiated until the image is displayed. This small change allows images to begin decoding immediately, which greatly speeds up loading times (especially on the answer side) of cards with a lot of images (AnKing).

[Luc-Mcgrady]

Is this the same as decoding the images synchronously? Would

    if (!img.getAttribute("decoding")) {
        img.decoding = "sync";
    }

give the same result?

Here is the relevant issue and pull request:

• Revisit async image decoding/preloading #4373
• Decode images asynchronously #4320

It is possible you would be interested in the upcoming reviewer in #4289 as this pre-loads the images of the next card, although this will not help for the first card.

[SelfishPig]

Whoops, you're right. I've fixed it. This change actually causes the backside images to be decoded while on the front of the card.

To demonstrate, here's a test card loading an 8000x8000 image.

Old behavior:

New behavior:

[Luc-Mcgrady]

Cool! Be sure to add yourself to the CONTRIBUTORS file so the CLI can pass.

[abdnh]

Thank you!