Tag: Python

Author TomPosted on
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Expression vs. Python Editor

It is common to prototype code in the Python Editor, and you may think to do this when you need write some code for an Expression. Beware, though they look deceptively similar, the full Gaffer API is not available in expressions, and references to plugs behave quite differently.

This sometimes leads to an attempt to call something like parent["Sphere"]["radius"].getValue() in an expression, and an exception like the following :

ERROR   [Execution error] Expression1.__execute :"python/Gaffer/PythonExpressionEngine.py", line 88, in execute
line 1, in <module> AttributeError: 'float' object has no attribute 'getValue'
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Author TomPosted on
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Labelled menu dividers

From 0.55.0.0 onwards, you can now label menu dividers. You can see an examples of this in the Editor Focus menu, which has both a title (in black) and two labelled dividers (dark grey).

To create these, simply add a label to your item when setting "divider" : True:

menu.append( "/Follow Divider",
  { "divider" : True, "label" : "Follow" }
)

Author TomPosted on
Categories Dev and Pipe TipsTags , ,

G4P – part 6 – Node defaults

For this instalment in our ground-up series about integrating Gaffer into a pipeline, we cover how to change node defaults.

All Gaffer nodes have plugs, whether they are visible in the Graph Editor for easy connection, or in the Node Editor as settings. These plugs have default values defined by the node’s programming. It may be the case however, that these defaults aren’t the most useful values for your use. To help with this, Gaffer allows you to provide your own, “user” defaults.

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Author TomPosted on
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G4P – part 5 – File Browser Bookmarks

In this instalment of the Gaffer for Pipeline series of ‘ground up’ posts, we look at adding custom bookmarks to the various Gaffer browsers. We’ll recap the tutorial from the Gaffer docs, introduce dynamic bookmarks and look at Gaffer’s own categories in more detail.

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Author TomPosted on
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Gaffer for pipeline – part 4 – which version?

When writing pipeline tools, it’s often useful to know which Gaffer version you are running in. In python, the Gaffer.About module is your friend:

import Gaffer
print( Gaffer.About.versionString() )
print( Gaffer.About.majorVersion(), Gaffer.About.minorVersion() )

We also define a (script + ABI) ‘compatibility’ version, that, as we use SemVer – is effectively tied to the milestone + major version:

print( Gaffer.About.compatibilityVersion() )
Author TomPosted on
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Scripting Box nodes

Gaffer’s Box node is a staple building block sharing chunks of node graph (via the Reference system), or quickly building tools via expressions and promoted plugs.

The Gaffer docs have a page covering Box nodes and how to use them. In this post we take a quick look at how to re-create a simple GroundPlane tool made in the UI, using only Gaffer’s python API.

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Author TomPosted on
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Gaffer for pipeline – part 3 – Compute cache size

Like many other applications that calculate data on-demand, Gaffer has a memory cache that can increase performance in UI sessions if you have RAM to spare.

The default size (1GB) is somewhat conservative as to ensure we don’t use up all the resources of more modest machines when Gaffer is used out-the-box. It is easy to increase the limit though, which can bring performance gains in real-world production scenarios.

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Author TomPosted on
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Gaffer for pipeline – part 2 – Customisation mechanisms

Continuing our bottom-up look at Gaffer from a pipeline perspective, in this instalment we look at the fundamentals of how to Gaffer is configured. We will cover:

  • Environment variables
  • Settings and Preferences
  • Gaffer’s Metadata system
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Author TomPosted on
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Gaffer for pipeline – part 1 – App structure and startup

It can be hard to know where to start when you first start integrating a new application into a pipeline. This post is the first part in a series that takes a bottom-up approach and brings together a few helpful links for getting started with Gaffer configuration, scripting and development.

In this part, we take a look at how the gaffer application is structured, and what happens at startup.

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