# ISAAC¶

This is a plugin for the in-situ library ISAAC [Matthes2016] for a live rendering and steering of PIConGPU simulations.

## External Dependencies¶

The plugin is available as soon as the ISAAC library is compiled in.

## .cfg file¶

Command line option

Description

--isaac.period N

Sets up, that every N th timestep an image will be rendered. This parameter can be changed later with the controlling client.

--isaac.name NAME

Sets the NAME of the simulation, which is shown at the client.

--isaac.url URL

URL of the required and running isaac server. Host names and IPs are supported.

--isaac.port PORT

PORT of the isaac server. The default value is 2458 (for the in-situ plugins), but may be needed to be changed for tunneling reasons or if more than one server shall run on the very same hardware.

--isaac.width WIDTH

Setups the WIDTH and HEIGHT of the created image(s).

--isaac.height HEIGHT

Default is 1024x768.

--isaac.direct_pause

If activated ISAAC will pause directly after the simulation started. Useful for presentations or if you don’t want to miss the beginning of the simulation.

--isaac.quality QUALITY

Sets the QUALITY of the images, which are compressed right after creation. Values between 1 and 100 are possible. The default is 90, but 70 does also still produce decent results.

The most important settings for ISAAC are --isaac.period, --isaac.name and --isaac.url. A possible addition for your submission tbg file could be --isaac.period 1 --isaac.name !TBG_jobName --isaac.url YOUR_SERVER, where the tbg variables !TBG_jobName is used as name and YOUR_SERVER needs to be set up by yourself.

## .param file¶

The ISAAC Plugin has an isaac.param, which specifies which fields and particles are rendered. This can be edited (in your local paramSet), but at runtime also an arbitrary amount of fields (in ISAAC called sources) can be deactivated. At default every field and every known species are rendered.

## Running and steering a simulation¶

First of all you need to build and run the isaac server somewhere. On HPC systems, simply start the server on the login or head node since it can be reached by all compute nodes (on which the PIConGPU clients will be running).

## Functor Chains¶

One of the most important features of ISAAC are the Functor Chains. As most sources (including fields and species) may not be suited for a direct rendering or even full negative (like the electron density field), the functor chains enable you to change the domain of your field source-wise. A date will be read from the field, the functor chain applied and then only the x-component used for the classification and later rendering of the scene. Multiply functors can be applied successive with the Pipe symbol |. The possible functors are at default:

• mul for a multiplication with a constant value. For vector fields you can choose different value per component, e.g. mul(1,2,0), which will multiply the x-component with 1, the y-component with 2 and the z-component with 0. If less parameters are given than components exists, the last parameter will be used for all components without an own parameter.

• add for adding a constant value, which works the same as mul(...).

• sum for summarizing all available components. Unlike mul(...) and add(...) this decreases the dimension of the data to 1, which is a scalar field. You can exploit this functor to use a different component than the x-component for the classification, e.g. with mul(0,1,0) | sum. This will first multiply the x- and z-component with 0, but keep the y-component and then merge this to the x-component.

• length for calculating the length of a vector field. Like sum this functor reduces the dimension to a scalar field, too. However mul(0,1,0) | sum and mul(0,1,0) | length do not do the same. As length does not know, that the x- and z-component are 0 an expensive square root operation is performed, which is slower than just adding the components up.

• idem does nothing, it just returns the input data. This is the default functor chain.

Beside the functor chains the client allows to setup the weights per source (values greater than 6 are more useful for PIConGPU than the default weights of 1), the classification via transfer functions, clipping, camera steering and to switch the render mode to iso surface rendering. Furthermore interpolation can be activated. However this is quite slow and most of the time not needed for non-iso-surface rendering.

## Memory Complexity¶

### Accelerator¶

locally, a framebuffer with full resolution and 4 byte per pixel is allocated. For each FieldTmp derived field and FieldJ a copy is allocated, depending on the input in the isaac.param file.

negligible.

## References¶

Matthes2016

A. Matthes, A. Huebl, R. Widera, S. Grottel, S. Gumhold, and M. Bussmann In situ, steerable, hardware-independent and data-structure agnostic visualization with ISAAC, Supercomputing Frontiers and Innovations 3.4, pp. 30-48, (2016), arXiv:1611.09048, DOI:10.14529/jsfi160403