High Definition Render Pipeline Glossary

General terms

atmospheric scattering:

Atmospheric scattering is the phenomena that occurs when particles suspended in the atmosphere diffuse (or scatter) a portion of the light, passing through them, in all directions.

bokeh:

The effect that occurs when a camera renders an out-of-focus point of light.

channel packing:

A channel-packed Texture is a Texture which has a separate grayscale image in each of its color channels.

Exponential Variance Shadow Map:

A type of shadow map that uses a statistical representation of the Scene's depth distribution and allows for the filtering of data stored in it.

face:

A face refers to one side of a piece of geometry. The front face is the side of the geometry with the normal.

face culling:

Face culling is an optimization that makes the renderer not draw faces of geometry that the camera can not see.

f-number:

The ratio of the focal length to the diameter of the camera lens. HDRP technically uses t-number, but since Cameras in Unity are optically perfect, f-number and t-number are identical.

Nyquist rate:

The minimum rate at which you can sample a real-world signal without introducing errors. This is equal to double the highest frequency of the real-world signal.

physically-based rendering (PBR):

PBR is an approach to rendering that emulates accurate lighting of real-world materials.

ray marching:

An iterative ray intersection test where your ray marches back and forth until it finds the intersection or, in a more general case, solves the problem you define for it.

texture atlas:

A texture atlas is a large texture containing several smaller textures packed together. HDRP uses texture atlases for shadow maps and decals.

Normal mapping

tangent space normal map:

A type of normal map in the UV space of the GameObject. You can use it on any Mesh, including deforming characters.

object space normal map:

This contains the same details as the tangent space normal map, but also includes orientation data. You can only use this type of normal map on a static Mesh that does not deform. This normal map type is less resource-intensive to process, because Unity does not need to make any transform calculations.

bent normal map:

HDRP uses the bent normal to prevent light leaking through the surface of a Mesh. In HDRP, bent normal maps can be in tangent space or object space.

Aliasing and anti-aliasing terms

aliasing:

Describes a distortion between a real-world signal and a digital reconstruction of a sample of a signal and the original signal itself.

fast approximate anti-aliasing (FXAA):

An anti-aliasing technique that smooths edges on a per-pixel level. It is not as resource intensive as other techniques.

spatial aliasing:

Refers to aliasing in digital samples of visual signals.

temporal anti-aliasing (TAA):

An anti-aliasing technique that uses frames from a history buffer to smooth edges more effectively than fast approximate anti-aliasing. It is substantially better at smoothing edges in motion but requires motion vectors to do so.

Lighting terms

illuminance:

A measure of the amount of light (luminous flux) falling onto a given area. Differs from luminance because illuminance is a specific measurement of light whereas luminance describes visual perceptions of light.

luminous flux:

A measure of the total amount of visible light a light source emits.

luminous intensity:

A measure of visible light as perceived by human eyes. It describes the brightness of a beam of light in a specific direction. The human eye has different sensitivities to light of different wavelengths, so luminous intensity weights each different wavelength contribution by the standard luminosity function.

luminosity function:

A function that describes a wave that represents the human eye’s relative sensitivity to light of different wavelengths. This wave corresponds weight values, between 0 and 1 on the vertical axis, to different wavelengths, on the horizontal axis. For example, the standard luminosity function peaks, with a weight of 1, at a wavelength of 555 nanometers and decreases symmetrically with distance from this value.

punctual lights:

A light is considered to be punctual if it emits light from a single point. HDRPs Spot and Point Lights are punctual.

Rendering Artifacts

disocclusion

A rendering artifact that describes the situation where a GameObject that was previously occluded becomes visible.

ghosting

A rendering artifact that describes the situation where a moving GameObject leaves a trail of pixels behind it.

z-fighting

A rendering artifact that describes the situation where two or more GameObjects have approximately the same value in the z-buffer. This causes the GameObjects to appear to flicker.