Tracking revisions with Git¶
BlenderBIM supports tracking the development of your IFC files with a Git repository.
BlenderBIM is an IFC file editor, you can create or load an IFC project, change, add or remove BIM objects and save to disk. A Git repository is a special folder on your computer where text files, such as IFC files, can be efficiently stored and past versions recalled.
Git is also a tool to share files with other people, transmitting only file changes, and allowing multiple people to keep local copies of the same repository up-to-date.
Note
If you don’t already have Git installed on your system, you will need to Download from the Git website. You may have to restart Blender after installation.
Adding your IFC file to a repository¶
First, save your file to disk. If the folder is already a repository you can Add the file in the IFC Git panel to tell Git you want to track it, otherwise BlenderBIM will offer to convert the folder into a repository.
Warning
You probably don’t want to turn your entire HOME or User folder into a Git repository. Create one folder per project, this folder can contain multiple IFC files, optionally in subfolders, plus any resources needed to support them.
After adding an IFC file, this action will appear as the most recent item at the top of the revision list.
‘Committing’ changes¶
As you work on your IFC project, save the file regularly as usual. When you get to a point where it would be useful to later retrieve this state, you need to commit this to the Git repository. BlenderBIM gives you three options:
Showing uncommitted changes will temporarily highlight the differences between the saved file and the last committed revision. Green objects are new and blue objects exist in the previous revision but have since been modified.
Discarding uncommitted changes will throw away all your saved changes and revert the model to the previous revision.
Committing changes will save this state of the model in the repository, along with a short commit message, the date, and your author details.
Tip
All revisions need to have some sort of commit message. Typically this should be kept to 50 characters or less, but there is no practical limit, consider that this message may appear in various places, including on drawings, web pages, email subject lines etc.. It is also best to describe the status of the revision rather than the changes, ie. “Kitchen now has a door” is better than “Add a kitchen door” - but this is a matter of taste.
Visualising differences¶
As you add commits, the revision list will build up. Usually you are working at the HEAD of a branch, ie. at the top of the list, but you can select items in the list to view commit metadata. You can also temporarily colourise the current model showing differences between this and any other saved revision - colours are the same as above: green objects are new to the current model, blue objects have changed in some way, and (if you have an older revision loaded) red objects have been deleted.
Viewing object history¶
The history of everything in the project is tracked in Git, the revision log for the currently selected object can be viewed with the BlenderBIM side-bar.
Retrieving Revisions¶
Colourising the model will show you which things are different, but it won’t show you how they are different. As long as you have no uncommitted changes, you can switch to the selected revision, this will load in BlenderBIM as a full model that can be viewed and even edited.
Warning
Switching to a different revision actually changes the file on disk before loading it in BlenderBIM. Don’t worry, the original hasn’t been lost, simply select the revision at the top of the list, switch back to that and you can continue as before.
Branching¶
Git supports a branched workflow. Say that you want to explore some design options, but don’t want to mess-up the primary design, you can fork off any revision into a new branch and work on this without breaking anything in any other branches.
Note
The primary branch in a Git repository is usually called main, though this is a convention, and older versions of Git call it master. Branch names should be short, but can contain unicode characters, emojis etc… Branch names can’t contain spaces, and have some other minor limitations - BlenderBIM will not allow you to create invalid branch names.
To create a new branch from the current HEAD (ie. the top of the revision list) enter a branch name when committing. Leaving this field empty just adds a normal commit without creating a branch, however committing a change to an earlier revision necessarily implies a new branch, so BlenderBIM will insist that you give it a name.
Each branch can now be navigated separately in the revision list, to switch between branches, and to any previous revision in any branch, select the revision you are interested-in and switch as before.
Tip
Conceptually a local branch is equivalent to a remote fork in somebody else’s copy of your repository, and indeed by adding a remote you can fetch their work into a remote branch in your local repository.
Merging¶
Warning
Merging is experimental functionality. There are various circumstances where a merge will fail, don’t worry, this won’t break your model but you may not want to rely on this functionality without having some experience of what changes are likely to merge and what won’t.
You can merge changes that exist in a selected revision into the current model, even if changes have been made in both revisions - as long as these changes don’t directly conflict.
Note
Merging requires the ifcmerge tool installed in your PATH, if it is not installed the merge operator will not be enabled.
When two branches have diverged, merging an IFC model requires conflict resolution (because added entities may inadvertently reuse the same Step-IDs), this means that data on one side or the other may be rewritten by BlenderBIM in order to accomodate both sets of changes. ie. the merge process is asymmetrical. BlenderBIM privileges data in the remote origin/main branch over the local working branch, similarly it privileges data in the local main branch over any other local working branch. The practical result of this is that branches branched-off the main branch can generally be merged back into main, but any sub-branches of these will need to be merged back into their parent-branch before merging the parent-branch back into main.
Remote operations¶
Git is a distributed revision control system, your local repository can be a version of a remote repository and vice-versa. This is conceptually similar to local branching except this remote repository could belong to someone else or could be hosted by an online Git-forge service.
Your repository can have multiple remote repositories registered, each can have potentially multiple branches.
BlenderBIM allows you to make a local clone of a remote repository. You will need to provide a URL origin to fetch, and an empty local folder to become the local repository.
The Fetch operator retrieves new data from the remote repository. This isn’t automatically merged, each branch fetched from the remote repository appears as a branch that can be browsed, switched-to or merged just like a local branch. These remote branches have prefixed names, eg. origin/main.
Once you have committed changes to your local repository, the Push operator tries to update the remote branch using changes from the selected local branch.
Warning
Remote repositories can be accessed in multiple ways; ssh, ftp or https protocols, for example, can require authentication. This authentication may expect you to generate and upload ssh keys, store API tokens, save username/password pairs, or use some other form of credential. BlenderBIM can’t configure these credentials for you, follow the configuration instructions provided by your online service before trying actions that require authentication.
Using other Git tools¶
BlenderBIM is not a full Git user interface, but it provides most of the tools you will need for day-to-day usage. In general if you need other Git functionality you can use external Git tools with your repository and any changes will be reflected in the BlenderBIM UI.