Half Life 2: Lost Coast HDR overview

Lost Coast / Source HDR Feature Set:

HDR rendering encompasses many different techniques and Doug revealed in detail exactly what Valve have planned for Half Life 2: Lost Coast, almost in an effort to distance themselves from other developers on this new digital frontier.

For example, Lombardi says of Blooming: "This feature has been added to other applications and is often mistaken as a full implementation of HDR," - one reason why he was keen to talk to us to help clear the air surrounding HDR rendering.

Interestingly, the following featureset is described as "our definition of HDR for Lost Coast " by Valve, and encompasses only "our initial implementation of HDR into the Source Engine development", hinting that not only can we expect to see HDR in other Source Engine games, but that there may well be further rendering tricks added to the library in the future.

For now, here is HDR a la Valve:

Blooming:

Used by designers to create a "blurred effect" on the bright edges in a scene, emulating a camera's overexposure.

HDR Skybox:

Authored by painting multiple exposures of the sky to allow for real-time exposure adjustment. For Lost Coast, over 16 variations of the HDR skybox were created.

HDR Cube Maps:

Generated by the engine, using the HDR skybox in conjunction with the HDR light sources and HDR light maps. HDR Cube Maps allow for an object's reflection to be cast in a manner that more accurately corresponds with the brightness of the source.

HDR Water Reflection/Refraction:

Wherever the reflection of a light source is extremely bright, "white hot" spots occur along with blooming on water. A similar effect may be witnessed when under water looking out toward the sun.

HDR Refraction Effect:

HDR light is transmitted through refractive materials, and takes on relevant properties of those materials (as when sunlight passes through the stained glass in Lost Coast's Monastery and then casts colored light).

HDR Light Maps:

Generated through a radiosity process, taking light bounces/global illumination into account. This may be witnessed inside the Monastery on Lost Coast, on walls opposite the windows where the sun is "blowing out" the wall.

HDR Light Sources:

Uncompressed light values provide a higher range of light values for designers to draw from in any given scene.

Exposure Control:

Enable "eye adjustments" to allow you to see a different range of details in dark scenes than in overbright areas.

On the next page, we will explore HDR in more detail, and look at the influence that Exposure Control and Dynamic Aperture has on what you will see in the game...