  The ALICE Collaboration at CERN developed a 3D visualisation tool capable of
displaying a representation of collected collision data (particle trajectories,
clusters and calorimeter towers) called the Event Display. The Event Display is
constantly running in the ALICE Run Control Center as part of the Quality
Assurance system, providing the monitoring personnel with visual cues about
possible problems of both hardware and software components during periods of
data gathering. In the software, particle trajectories (which are curved due to
presence of magnetic field inside the detector) are generated from physical
parameters of detected particles, such as electrical charge and momentum.
Previously this process in the Event Display used a uniform, constant magnetic
field for these calculations, which differs from the spatial variations of the
real magnetic field and does not model one of the two magnets used in the
detector. Recently, a detailed model of ALICE magnetic field was made available
as a shader program for execution on the GPU. In this work we attempt to
implement the reconstruction algorithm in a shader form as well, allowing us to
combine it with the detailed model to create a full solution for rendering
trajectories from collision event data directly on the GPU. This approach has
several possible advantages, such as better performance and the ability to
alter the magnetic field properties in real-time. This was not previously done
for ALICE and as such could be used in the future to upgrade the Event Display.
