Basket arch with given width and height

update: when using Blender 2.73 or later make sure you get the latest version (20150206 or newer) from GitHub.
In a previous article I showed a simple addon to create a basket arch with a given width. This update adds the possibility to set the height as well. A height of 0 will give you the classic basket arch and it will silently ignore width/height ratios > 4 or < 2 (in which case it will revert to a classic arch).

For width/height ratios close to 1.0 the fit isn't perfect and although I followed the instructions on (pdf) closely the curves for the classic arch and the one with known height are not exactly the same although to be honest I not 100% sure what to expect. It might also be due to numerical inaccuracies.

In the end you might be better of scaling the arch in the z-direction.

The previous article contains source code link and installation instructions.

open shading language for blender: promotion

to celebrate thanksgiving & sinterklaas my book Open shading language for Blender is now available for just $3.99!

This promotion is valid until 5 december, with promotion code UE42Z.


Addon: Creating a basket arch in Blender: better symmetry

A slightly improved version of the addon is available on GitHub. It corrects the slight assymetry between the left and right sides (the bottom most vertices were not at the same height)

You can install it in the usual way: File->User preferences->Addons->Intall from file. Don't forget to check the 'enable addon' box. It will the be available from the Add Mesh menu in the 3D view.
If you already installed the first version do not forget to remove the old version firs: File->User preferences->Addons->Add Mesh->Basket arch->Remove now points to

It proved too cumbersome to keep my old website ( online so I decided to simply point it to my most popular blog. In the future I may try to get some old content back online but don't hold your breath :-) (The most interesting stuff is on this blog anyway)

In a couple of days any visitors to may find themselves suddenly redirected to, so don't worry if you see something unexpected. The blog itself will of course not be affected and I will continue to publish articles there quite frequently.

Addon: Creating a basket arch in Blender

Recently I was thinking about a visualization of some rooms in our house. These rooms were once separate but the wall has been broken through and the arch between them has a very specific form: a basket arch, aka three centered arch. This is a form widely used not only indoor but also for example for many 17th century bridges and is not entirely trivial to construct as it involves matching three circle segments at their tangents. So I constructed a small addon to create basket arches ;-)

Availability and possible improvements

The addon is available on GitHub. You can install it in the usual way: File->User preferences->Addons->Intall from file. Don't forget to check the 'enable addon' box. It will the be available from the Add Mesh menu in the 3D view.

The addon constructs what is called a classical three centered arch, that is you can only choose the width while the height has then a fixed proportion. It might be a good idea to add the variant where you can also specify the height, which will give a squeezed arch that is has not quite the same shape as a classical arch that is scaled in the z-direction.

Currently the vertices in the arch a distributed with more or less even spacing along the circle. Because we use the angle along a circle segment the last vertex may or may not touch the ground. This is however hardly visible and since I intended this addon for visualization rather than CAD I thought i good enough. I might fix it though in the near future.

Full book review: Blender 3D Basics Beginner's Guide, second edition

Blender 3D Basics Beginner's Guide, second edition

The first impressions on reading the first edition of this book were that it was well written and the second edition doesn't change that. The writer clearly has thought about how to present the reader with projects that provide a smooth learning curve. No details are left out and animation, not just modeling and rendering, is a focal point from page one.

While reading the book you clearly get the feel you are getting somewhere. Many easy to follow steps guide you through subjects like camera work, animating, rendering a final compositing and the book even touches on that all important point of animation: telling a story. At the end the reader will be able to create a small animated movie (even in anaglyphic 3d!).

It helps of course that for almost every small step sample files are available for download and the pdf version of the ebook is in color, a necessity for books about graphics in my opinion (although the .mobi version read just fine on my Kindle)

The second edition doesn't add much in terms of content but it is updated for Blender 2.7, which is nice. It still doesn't cover character animation, (which is an advanced subject, but something about armatures would have been nice, even for non-character animation), while texturing, especially UV mapping, is still hardly touched upon. Cycles, the Blender's new render engine, gets a little bit more coverage now but not as much as it deserves. I don't think this is a major issue though: thousands of fine animations have been made with Blender's internal renderer and thousands will be.

Conclusion: This is an excellent book for Blender novices. Reading this book gives the aspiring Blender animator the biggest chance of actually finishing something instead of leaving the reader with some boring technical experiments.

Selecting from property lists in Blender addons

In a previous article I reported on the difficulties that crop up when you want to present a dynamic list of choices, like a dropdown to select an object in a scene. Now it appears that for many situations there is a better way that was somewhat hidden in Blender's API docs: prop_search().
What this poorly documented function does is putting a widget in the layout of your addon that lets the user select an item from a property list that is part of an object the name of which subsequently assigned to a property on another object.
That may sound a bit cryptic at first but say you want to let the user choose a vertex group on the active object and store the name of this chosen vertex group in a string property. Then all you have to do is to define that property in your operator and call prop_search() in the draw() function:
vertexgroup = StringProperty(name="Vertex group")
def draw(self, context):
    layout = self.layout
    # get the mesh data of the active object
    ob =
    # display a vertex choice widget that assign to our string property
    layout.prop_search(self, "vertexgroup", ob, "vertex_groups", text="Vertex Group")
It automatically assigns a proper icon as well:

This works for basically anything that is a bpy.types.bpy_prop_collection, like objects in a scene or vertex groups in mesh data. There's also a prop_enum() that lets you select an item from a enumerated property.

book review: Blender 3d basics beginners guide - second edition

Packt asked me to review the second edition of Blender 3d basics beginners guide.

A long time ago I reviewed the first edition and my impression then was quite positive. Character animation however was not covered and uv mapping and cycles were underrepresented so I am curious whether these subjects are better covered in this new edition.

Stay tuned for a full review.

DryStone: create irregular stone walls, uvs and random vertex colors

I commited a small feature update for the Drystone addon. It now generates a (possibly random) uv-map and a vertex color layer with random colors. This makes it quite simple to use a stone texture for the whole wall while enhancing the effect of separately cut stones and slightly irregular coloring.

(The texture used in the image was RockSediment0105_1_L.jpg from CGTextures)
The node setup used for the image looks like this:


The updated addon is available from GitHub.