1254168 - createImageBitmap still decodes synchronously on main thread

Status: RESOLVED DUPLICATE of bug 1189632

(Core :: Graphics: Canvas2D, defect)

Description

[ash]

Steps to reproduce:

Visit the following URL: https://www.scirra.com/labs/imageConversion/

1. Click the "Load images as blobs" button and wait for them to finish downloading.
2. Click the button to convert via drawImage/getImageData and note the time to complete.
3. Click the button to convert via createImageBitmap/getImageData and note the time to complete.


Observed results:

On my quad core development machine, results are approximately:
drawImage/getImageData: 750ms
createImageBitmap/getImageData: 700ms

If you record this in the Performance tab of developer tools then switch to the JS Flame Chart, you can see BlobToImageDataViaImageBitmap calls synchronously queued with "Graphics" on the main thread.


Expected results:

createImageBitmap should lift the heavy work of image decoding off the main thread. This should allow batch processing like this to complete much faster since it can use all available CPU cores. Instead createImageBitmap appears to be no faster than the equivalent previous method of synchronously decoding on the main thread, which seems to defeat the purpose of createImageBitmap.

Comment 1

[:Gijs (out until Jan 5th; he/him)]

Seth, canvas or imagelib?

Comment 2

[ashley]

This looks like a duplicate of bug 1189632

Comment 3

[:Gijs (out until Jan 5th; he/him)]

(In reply to ashley from comment #2)
> This looks like a duplicate of bug 1189632

Indeed!