Atmospheric Scattering

At long long last I have got a grip of atmospheric scattering. Decades implementation of atmospheric scattering is based on Sean O'Neill's amazing research. In the video below you can see the sun rising in the sky as the camera moves around the planet. The word planet is used with grace as the planet is simply a smooth sphere which was procedurally generated with recursive subdivision. (See Post below). Close to the end of the video the rendering switches to wire frame and you can see the planet subdividing by another level.

As always there is a list of improvements to make. The planet is currently rendered in software, each face rendered separately. There is also no culling. Adding hardware acceleration and efficient culling should greatly improve performance. The subdivided implementation of the sphere allows easy culling of vast numbers of faces with a few checks.

I am also going to look more detailed at realtime fractal terrain generation, possibly with Perlin Noise so as I dubdivide the planet as the camera gets closer the result will be a details, rich looking terrain.

Procedural Sphere

While implementing my Sky Dome for atmospheric Scattering a number of issue quickly became noticeable. A sphere generated using the OpenGL function gluSphere or loaded from a mesh file had vertex compression at the poles. This usually causes texture compression/distortion which is naturally very undesirable.

To maintain Decade's procedural capability and to remove the issues with the previous implementation I created my own Sphere function by recursively subdividing a cube until the required resolution was achieved.

Below the two solutions can be seen side by side. On the left is the Sphere created with gluSphere or loaded from a file. The vertex compression is immediately obvious. The size of the face depends on which segment it exists, with faces getting smaller closer to the poles. On the right is my procedurally generated sphere. As you can see there is no vertex compression at the pole. In fact no pole is visually obvious. Due to the subdividing nature of the algorithm each face in the sphere is the exact same size.


I believe I may have achieved allot more than just creating a sky dome with this implementation. Creating a universe with procedural planets has always been on the wish list for Decade but I never knew where to begin. The recursive subdivision appears to be an ideal solution for this. It has level of detail and efficient culling properties automatically built in.

The level of the quad tree rendered defines the level of detail of the planet. Since the root of the planet is 6 quads, it is easy to bounds check these against the frustum and quickly remove unseen areas of the planet and the same process can be repeated for each of the child levels of the quad tree.


By using the above algorithm along with some height maps I believe rendering a full planet should be possible. I look forward to the day when I can roam a planet in Decade then jump in a space ship, fly away and land on another planet.

Oil Painting

For another personal project (web based) I have worked on some image processing, hence the lack of updates this month. Rather than let the new code go to waste I have applied it to Decade too see the results. Here is a normal screen shot of Decade

and here is Decade as an Oil Painting.

I am happy with the results, although now a little unsatisfied that the manipulation is not real time. I'm not sure of the possibility of writing a Pixel Script to do this in real time because it requires sampling multiple pixels in order to create the smudged Oil Paint effect. Despite this I still plan to at least try and implement an Oil Painting script sometime. It would be nice to make a game where it appears that the whole world is painted, and perhaps the levels of the game could be based on classic painting by Da Vinci, Picasso etc.

I have also been working on Atmospheric Scattering this month but because of my other commitments have not yet fully integrated with Decade. I will try and get a video update soon to at least give a taster of my progress.

The other day I found a shortcut to my old website. It has been almost 3 years since it was updated. Hosted on an Irish telecoms provider, I do not seem to be able login to my account from outside Ireland so it has remained static since I left. It has some fond memories for me. This was my start in game programming as a hobby. The host where my game demos were stored is no longer active so you cannot download anything. If you would like to try anything leave a comment and let me know. I will then find the game in my archive and upload it.