Basic image blur algorithm runs 20-100x slower in Dartium than JS

[blois]

Attached is a simple image blur application using a fairly object-oriented (yet usually efficient) scanline blur implementation.

The code is implemented in both Dart and Javascript, with absolute minimal delta.

On my machine, Dartium takes ~5000ms to process the image, dart2js is ~150ms and vanilla JS is 50ms.

Note that changing the pixel data types from Uint8ClampedArray (native type for Canvas data) to List<int> and an intermediate data list from Float32Array to List<int> moves this from 5000ms to 1600ms. The Uint8ClampedArray conversion is problematic as it incurs a heavy duplication of the image data which is not accounted for in the 1600ms. These arrays should really remain in their native data type as much as possible.

I'm sure there are many optimizations that could be done to this code, but it doesn't feel so terribly inefficient to warrant these performance differences.

---

Attachment:
blur.zip (223.55 KB)

Set owner to @sgmitrovic.
Added this to the M2 milestone.
Added Triaged label.

[blois]

Adding repro which runs from the local filesystem.

---

Attachment:
blur_local.zip (6.98 KB)

[iposva-google]

I expect every single access to the Uint8ClampedArray (pixel data) and the Float32Array (pixel data window) to go through a native call since Dartium is not using any of the scalar list support.

There are two things to be done here:

• Take the algorithm in this example and disassociate it from all dart:html code to make it a standalone benchmark using dart:scalarlist as well as just regular Lists.
• Use the dart:scalarlist library in Dartium by fixing issue Acessing imageData is way too slow in the dart vm #3312.

We will continue the VM investigation of standalone performance here.

Adding clamped Uint8ClampedList to VM. Will follow by optimizing access to it.

[iposva-google]

Removed this from the M2 milestone.
Added this to the M3 milestone.

Issue #7347 has been merged into this issue.

Optimized access with r16666. Waiting on Dartium to switch to VM's clamped array

---

Set owner to antonm@google.com.
Removed Area-VM label.
Added Area-Dartium label.

[anders-sandholm]

Removed this from the M3 milestone.
Added this to the M4 milestone.

[DartBot]

This comment was originally written by antonm@google.com

---

Should have been fixed now. Please, reopen if not the case.

---

Added Fixed label.