Volumetric lines 2 + News

Hello!

Sorry for the long time silence but I have been very busy recently: PhD writing, not accepted paper I have to modify, internship students to take care, researchers who want to use my engine, etc... Now it's better, I will have more free time by the end of the week.

So what are the news! Volume Lines 2 demo is on-line. In fact, I have submitted it to GpuPro2 but it was not accepted: I expected this answer because indeed the method is pretty simple. The results are nicer than previous volumetric lines but it requires geometry shaders and it is more computationally expensive.

Also, I started to work in Virtual Textures few weeks ago. I have the low resolution feedback buffer working with required pages to load, indirection table, etc. Just need to load required pages from the disk to GPU virtual memory in a separate thread together with a LRU cache. I will work again on it soon.

The development of my light-pre pass renderer with relief mapping is... well... deferred. :/ I have a lot of optimization ideas and I hope I can show you more about it soon.

Finally, I will go to Siggraph 2010 this year as an attendee! :) Many courses and talks to attend! It will be hard to attend every sessions I would like to but, I will do my best. I may talk about this conference, show some pictures and report about courses/talks on this blog. Maybe I will be able to meet some of you overthere! :D

New volumetric lines method

Hi readers,

I have been working on many things recently. One of these things is a new volumetric line algorithm!
My previous method (basically the same as the one proposed in ShaderX7) was really fast and yields good looking result. I think that's why it was successfully used in the iPhone game PewPew. The only thing about this method is that you should avoid looking lines along their direction because, in this case, the trick I use become visible. Also, it was not possible to shade the line based on its thickness from current viewpoint.
Another method has been proposed by Tristan Lorach to change volumetric lines appearance based on the angle between view and line directions. However, line appearance was represented by only 16 texture tiles and interpolation between them was visible.

The new method I propose is able to render capsule like volumetric lines with any width and for any point of view, i.e. you can look inside/through the line. It also allows the use of thickness based visual effects.

Here is the overall algorithm of my new method:

1. Extrude an OOBB around the volumetric line having the same width as the line. This is done using a geometry shader computing triangles strips from a single line.
2. Compute closest and farthest intersections between view ray and capsule using geometric methods and/or quadratic functions resolution. This is done in the OOBB frame reference.
   
3. Compute thickness based on capsule intersections and environment depth map.
   
4. Shade the volumetric line based on it's thickness.
   

It is pretty simple but efficient. I will not go into the details right now: there will be a post on my website soon. I will just show some early screenshots from the current version:

The capsules representing the volumetric lines
filled with a white color

line radius can be changed


Thickness based shading and intersection with the environment

View from above and under the ground

The thickness is correct,
even if the camera is inside the volumetric lines

Volumetric lines

Four years ago, A method to render volumetric lines has been proposed by Tristan Lorach at nVidia (link). I have found this method very interesting but, to my opinion, texture interpolation simulating change in point of view were too visible. Three years ago, I decided to propose my own volumetric line rendering method as visible on my website. My method does not allow as much visual effect as the one of nVidia but at least you can change the appearance of lines using a simple 2D square texture. Each line is rendered using 6 triangles and all computations are done in the vertex program. The drawback with my method is that when lines' width is very large and their direction is parrallel to the view direction, the trick I use is visible. However, for line which are not large, this problem is rarely noticeable.

Screen shot of the volumetric lines.
Because the line on the bottom is large, the trick I use is visible.In this screenshot, another appearance texture is applied.

Recently, an article published in ShaderX7 proposed a method very similar, if not same, to the one I propose. I should have written an article before... At that time, I was beginning my Master study and I cannot imagine this would be possible.

Many people write to me in order to discuss this method, and I am really happy to see people using it. I am pleased to announce that my method is use in an iPhone game developed by a French guy as you can read on one if his post and blog. :)