Fog 2D Filters: Height, Cube, Sphere, Volumetric (BGE/UPBGE)

Here’s my implementation of Eric Lengyel’s halfspace fog (link to PDF article) originally published in Journal of Graphics Tool’s, Vol. 12, No. 2 (2007).

The GLSL filter is paired with a script that updates the uniforms, as the filter requires the camera position and orientation to properly render the fog in the world space.
While it may look as only a height fog, it is called halfspace because the fogged space can actually have any orientation:

The position and orientation is given by the empty containing the filter, as it would be expected.

Made in Blender 2.79, works with UPBGE 0.2/0.3.

The option ‘UseMistColor’ allows using as color source for the fog, this is convenient for changing the color in-game, rather than changing each RGB game property manually. By default, the mist color is the same as the background/horizon. This option doesn’t work in UPBGE 0.3.

Now it is possible to change the color of the fog with the color of the empty:

FogEmpty = scene.objects['HalfspaceFog']
FogEmpty.color = [0.4, 0.5, 0.6, 1.0] # RGBA, alpha is required, but not used.

It is initialized with the game properties ColorR, ColorG, ColorB.

Halfspace-Fog-2DFilter.blend (87.0 KB)


Looks great! Do you think this would be useful for fading out objects at the edge of a scene, or are the built-in Mist settings more performance-friendly?

A deferred fog could potentially have better performance, but I think you should try and see.

WOW… this is really cool.
I guess though there’s no start or fade in this type? Meaning I can’t set how far from the camera the fog starts at.
A kind of best of both worlds scenario, that what the UPBGE_0.3_glsl_mist does, but with height control like this one.

I don’t know if it’s possible that kind of setting with this fog. Maybe try enabling Squared and set the density really low, like 0.1. I’m personally not very fond of a fog that starts at a certain distance from the camera, it makes me feel I can’t never reach the fogged area.

Just getting some time to play with this… I think the fog density value works great for the distance from camera thing. This looks so good… can’t wait to drop it into my project. Looking forward to sharing it with y’al.

1 Like

I think I’ll just use this thread to dump some fog related filters I’ve been sitting on.

Fog Volume

A fog filter in the shape of a cube or a sphere, using tracing methods from this WEBGL Path Tracing demo (github).

The sphere option also support irregular scaling. The SoftEdge property controls the softness of the edges of the sphere, not the cube.

The color can be controlled with the color of the object, initialized with the properties ColorR, ColorG and ColorB; or with the mist color enabling UseMistColor.

For BGE and UPBGE 0.2/0.3.

FogVolume-2DFilter.blend (138.7 KB)

More to come…


Thank you for these! Looks much smoother than using Volume Scatter (which always flicker, at least on my PC)
Do I understand it correctly that this is a kind of elegant workaround for the Fragment- and Vertex-shaders like they used to work in previous BGE?

It’s likely that Eevee uses raymarching or a similar method for volumetrics, this filter is not volumetric, but it’s called fog volume because the fog is limited to the volume of a shape. This is how it works: the tracing functions traces the shape with a ray from the camera and return the entrance and exit intersection points. The distance between the exit point, or the geometry if it’s closer, and the entrance it is used to calculate the fog; if the distance to the geometry is less than the entrance point, which is always greater if the ray doesn’t intersects the shape, there is no fog.

Volumetric Fog

A volumetric fog (sun lamps shadows only) with the traditional ray marching technique.

These are the game properties you should pay attention to:

  • Sun Lamp: the name of the sun lamp whose shadows you want in the fog. Beyond this distance, the fog will stop existing (more on this later).
  • Max_Distance: the maximum distance from the camera to ray march the fog. If the sun follows the player/camera, you shouldn’t set this to a greater value than the shadow visible distance in front of the camera.
  • samples: this determines the quality of the fog; more samples = better quality, worse performance. It’s the amount of steps or layers used to make the fog, dividing Max_Distance by samples gives you the distance between steps: 25.0 / 70 = ~0.36 meters or BU. The steps are dithered with a random noise to reduce any flickering, more samples make the noise less visible, but if a portion of fog between shadows is smaller than the step size, the noise will still be visible.
  • Full fog: enabling the option will extend the fog beyond the maximum distance with a basic ranged fog. This will cover the sky/background, more or less depending on the clip end of the camera. Alternatively, you can use the default mist and set the start to the Max_Distance value; you may need to experiment with the falloff type to preserve the continuity between both fogs.

The color of the fog is given by the color of the material of the cube object, but it is also affected by the color of the sun lamp: a green sun will tint the fog green.
The mie scattering can be disabled of adjusted with the corresponding properties.

For performance reasons samples, Mie Scattering, Full fog and Debug fog are “hard coded” in the shader when it’s first created and won’t directly affect the fog if they are changed in game. To apply the changes you need to execute the script again, resetting the Always sensor will do.

It supports simple and VSM shadow types. The resolution of the shadow buffer affects the performance.

About UPBGE compatibility
In order to get the shadow buffer working in the shader, it’s necessary to bind it with the openGL wrapper module (bgl). In UPBGE 0.2, the filter works in the embedded player, but in the standalone player, glActiveTexture, essential for the buffer binding, raises a TypeError: 'NoneType' object is not callable, meaning the filter won’t work. Maybe it’s just me, but I get this on Windows and Linux. Overall, I found the bgl module to be less reliable on UPBGE, that’s why I do practically everything in BGE.
In UPBGE 0.3, you can’t get the shadow bind id through the sun lamp, shadowBindId was probably removed with the game engine and since sun lamps use cascaded shadow maps, there’s more than one shadow buffer per lamp.

Volumetric-Fog-2DFilter.blend (116.3 KB)