This commit implements the [depth of field] effect, simulating the blur
of objects out of focus of the virtual lens. Either the [hexagonal
bokeh] effect or a faster Gaussian blur may be used. In both cases, the
implementation is a simple separable two-pass convolution. This is not
the most physically-accurate real-time bokeh technique that exists;
Unreal Engine has [a more accurate implementation] of "cinematic depth
of field" from 2018. However, it's simple, and most engines provide
something similar as a fast option, often called "mobile" depth of
field.
The general approach is outlined in [a blog post from 2017]. We take
advantage of the fact that both Gaussian blurs and hexagonal bokeh blurs
are *separable*. This means that their 2D kernels can be reduced to a
small number of 1D kernels applied one after another, asymptotically
reducing the amount of work that has to be done. Gaussian blurs can be
accomplished by blurring horizontally and then vertically, while
hexagonal bokeh blurs can be done with a vertical blur plus a diagonal
blur, plus two diagonal blurs. In both cases, only two passes are
needed. Bokeh requires the first pass to have a second render target and
requires two subpasses in the second pass, which decreases its
performance relative to the Gaussian blur.
The bokeh blur is generally more aesthetically pleasing than the
Gaussian blur, as it simulates the effect of a camera more accurately.
The shape of the bokeh circles are determined by the number of blades of
the aperture. In our case, we use a hexagon, which is usually considered
specific to lower-quality cameras. (This is a downside of the fast
hexagon approach compared to the higher-quality approaches.) The blur
amount is generally specified by the [f-number], which we use to compute
the focal length from the film size and FOV. By default, we simulate
standard cinematic cameras of f/1 and [Super 35]. The developer can
customize these values as desired.
A new example has been added to demonstrate depth of field. It allows
customization of the mode (Gaussian vs. bokeh), focal distance and
f-numbers. The test scene is inspired by a [blog post on depth of field
in Unity]; however, the effect is implemented in a completely different
way from that blog post, and all the assets (textures, etc.) are
original.
Bokeh depth of field:
Gaussian depth of field:
No depth of field:
[depth of field]: https://en.wikipedia.org/wiki/Depth_of_field
[hexagonal bokeh]:
https://colinbarrebrisebois.com/2017/04/18/hexagonal-bokeh-blur-revisited/
[a more accurate implementation]:
https://epicgames.ent.box.com/s/s86j70iamxvsuu6j35pilypficznec04
[a blog post from 2017]:
https://colinbarrebrisebois.com/2017/04/18/hexagonal-bokeh-blur-revisited/
[f-number]: https://en.wikipedia.org/wiki/F-number
[Super 35]: https://en.wikipedia.org/wiki/Super_35
[blog post on depth of field in Unity]:
https://catlikecoding.com/unity/tutorials/advanced-rendering/depth-of-field/
## Changelog
### Added
* A depth of field postprocessing effect is now available, to simulate
objects being out of focus of the camera. To use it, add
`DepthOfFieldSettings` to an entity containing a `Camera3d` component.
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Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Bram Buurlage <brambuurlage@gmail.com>
