Possumwood

Synopsis

Possumwood (named after Sandbox Tree) is a graph-based procedural sandbox, implementing concepts of graph-based visual programming in a simple interface. It is intended to provide a user-friendly and accessible UI for experimenting with common computer graphics algorithms and libraries (e.g., OpenGL, CGAL, WildMagic, OpenCV).

Possumwood is built on top of a simple graph-evaluation engine and a Qt-based node graph editor, with an OpenGL viewport. Its main strength is its extensibility - it is trivial to implement new plugins supporting new libraries and data types, which allows free and user-friendly experimentation with parameters of each algorithm.

Possumwood is a sandbox, not a production tool. As a sandbox, it is quite open to radical changes and redesign, and for the time being it does not guarantee any form of backwards compatibility.

Possumwood is currently in active development, and does not pretend to be feature complete. It is not by any means meant to be a production tool, at least not yet. Any help is appreciated!

Table of contents

• Synopsis
• Installation
  • Launchpad PPA for Ubuntu 18.04+
  • Installation using Snap
  • Building from source
• Example setups
  • Opengl
  • Cgal
  • Lua mesh generation
  • Polymesh
  • Lua
  • Opencv basics
  • Opencv image ops
  • Opencv hdr
  • Lightfields import
  • Lightfields depth
  • Animation
• Tutorials
  • Basics
  • OpenGL / GLSL
  • Image manipulation
• Code Example
• API Reference
• Contributors
• License

Installation

Possumwood has been tested only on Linux (several distributions). While it should work on Windows, it has not been compiled or tested there. No support for MacOS is planned for the time being due to heavy dependency on OpenGL.

Launchpad PPA for Ubuntu 18.04+

On Ubuntu, the easiest way to install Possumwood is to use the snapshots PPA:

sudo add-apt-repository ppa:martin-prazak/possumwood
sudo apt-get update
sudo apt-get install possumwood

This will install Possumwood to your system, enabling to simply run possumwood command from any terminal.

Installation using Snap

Currently, Possumwood is released in Snap as a development/testing package only. The latest build and its status can be accessed here.

To install a testing version, please run:

sudo snap install --edge possumwood --devmode

This will download and install the latest successful build of Possumwood with its dependencies. To start the application, run possumwood from the command line. As a dev build, snap will not automatically update this installation. Moreover, snap skin support is currently rather rudimentary, making Possumwood not inherit the system look correctly.

Building from source

The project is structured as a standard CMake-built project. To build, just run these in the directory of the repository on any Linux distro:

mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=Release && make

And the result could be just run via ./possumwood or ./build/possumwood.

Example setups

Possumwood comes with a number of example setups that can serve as a starting point for experimentation.

Opengl

<table> <tr> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/01_simple.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> <td>

A simple OpenGL demo

A simple demo showing how to load an .obj file (positions, normals and topology) and display it using OpenGL.

Named vertex attributes p and n are loaded from an .obj file, and passed through to an OpenGL vertex/fragment shader setup. In later demos, this setup is wrapped-up in a subnetwork.

</td> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/01_simple_screenshot.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> </tr> <tr> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/02_auto_normals.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> <td>

Automatic normals

When an mesh file doesn't include explicit normals, it is relatively easy to use a fragment shader to "autogenerate" normals using screen-space derivatives dFdx() and dFdy(). This demo shows how to do that in Possumwood - just have a look at fragment_shared source.

</td> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/02_auto_normals_screenshot.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> </tr> <tr> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/03_turntable.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> <td>

Turntable demo

A simple shader setup passing a time value (i.e., the timeline value) as a uniform into the shader (together with viewport parameters). This value is then converted in the vertex_shader to a transformation matrix used to rotate a model.

</td> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/03_turntable_screenshot.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> </tr> <tr> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/04_wireframe.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> <td>

Wireframe using a geometry shader

Wireframe mode is one of the rendering modes of OpenGL. A similar but more controllable effect can be achieved by processing a model using a geometry shader, which allows to convert primitives to a different number of primitives of the same or different type.

This setup shows how to emit a line for each polygon edge of the input geometry using a program in geometry_shader. It also shows how to adjust the line width to screen resolution, maintaining the width independent to view parameters.

</td> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/04_wireframe_screenshot.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> </tr> <tr> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/07_geom_subdiv.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> <td>

Mesh subdivision in a geometry shader

While modern GPUs contain a bespoke functionality for subdivision, this simple demo shows how a similar (if limited) effect can be achieved using a simple geometry shader.

This demo implements a simple interpolative sudvision scheme with normal-based displacement. All subdivision computation is done in a geometry shader, with additional vertices and topology emitted by calling a recusive function. This approach is just a toy example, as it is strictly limited by the capabilities of individual GPUs - in practical applications, bespoke tesselation shaders perform much better.

</td> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/07_geom_subdiv_screenshot.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> </tr> <tr> <td> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> <img src="toolbars/01_opengl/08_pn_triangles.png" style="width:70px;"> <div style="width:290px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div> </td> <td>