ID 497388 - TimeBlur does not evaluate upstream Expression nodes

Problem summary
TimeBlur does not evaluate upstream Expression nodes. This issue occurs when viewing the result in the Viewer.

Customer reported version
Nuke 13.1v1

Customer reported platform
ubuntu

Steps to reproduce

This issue can be seen by opening the attached .nk script, or by following the steps below:

1) Open Nuke.

2) Create a Roto node.

3) Draw a Bezier shape in the Viewer, and set the Roto's output knob to rgba.

4) Create a TimeBlur node, but do not connect it to anything yet.

5) On the TimeBlur, set the shutter knob to 0.999.

6) Create an Expression node, downstream from the Roto.

7) On the Expression node, assign a variable called divisions and give it the expression (TimeBlur1.divisions)-1.

8) Add the following expression to the expr03 knob:

ceil(a*divisions)/divisions == ceil((frame%1)*divisions)/divisions

The Expression node should now look like the following:

​

9) Create a CheckerBoard node.

10) Create a Merge node and set to its operation to mask. Connect the A input to Expression node, and the B input to the CheckerBoard node.

11) Connect the TimeBlur downstream from the Merge and view the result in the Viewer.

Expected behaviour
The TimeBlur should evaluate the upstream Expression and display the correct result in the Viewer.

Actual behaviour
TimeBlur does not evaluate upstream Expression and the result in the Viewer is incorrect.

Workaround
In this case, you can workaround the issue by doing the following:

1) Create a NoOp node.

2) Create an integer knob on the NoOp node. In this example, I have named the knob frame_num.

3) Right click the userknob > Add expression... and enter frame.

4) You can then reference this knob on the Expression node, rather than calling frame directly. For example:

​

Reproduced by support
This bug has been reproduced in:
Nuke 13.1v1 - Windows 10 - Linux CentOS 7 - macOS 10.15 (Catalina)
Nuke 12.0v1 - Windows 10 - Linux CentOS 7 - macOS 10.15 (Catalina)
Nuke 9.0v1 - Windows 10

NOTE: In Nuke 12, the issue appears to happen less consistently when changing frames in the Viewer.

Earliest version tested
Nuke 9.0v1
- This issue appears to be in all versions of the product