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OpenGL Timer Query Tutorial

Jun 082011

In March, 2010, the Khronos group approved an extension to add timers to OpenGL. The version was 3.2. As of OpenGL 3.3 this functionality has become part of the specification.

As mention in the Very Simple Profile Library page, profiling is an essential technique to truly understand how to improve the performance of an application. Being able to get time measurements is important both in the development stage as well as during run-time after the application has been released. OpenGL Timer Queries allows us to profile the GPU. i.e. to determine the amount of time it takes to execute a command, or sequence of commands in the GPU.

A tutorial is available in here describing the OpenGL timer functions, showing how to use them, and describing a double buffer approach to prevent the application from being stalled while waiting for query results.

Instant Radiosity using Optix and Deferred Rendering

Tutorials No Responses »

Mar 292011

Graphics Runner blog. Instant Radiosity is a theoretically simple method. It traces paths from the primary light source and creates virtual point lights (VPL) when the path hits the scene. These VPLs approximate the reflected light from that region of the scene.

The path can then be reflected, possibly with a new random direction, and is further traced until it intersects the scene again. The decision to further pursue a path can be as simple as russian roulette. The approach in the Graphics Runner blog optimizes this by defining a grid of voxels and merging all the VPLs in each voxel into a single VPL. The scene is then lit with all the computed VPLs. Graphics Runner uses nVidia Optix for Ray Tracing. The article includes a small tutorial and provides some source code.