Donnerstag, 22. Mai 2014

Voxel Engine Update - 18 Level Octree & Copy Paste in Action

Copy and Paste works well now. Areas of voxels can be grouped to new entities for placing them in the scene. The size of the entire voxel data of the screenshot below on disk is just 1.3MB, which is quite OK. Thanks to my new graphics card, voxel raycasting and terrain rendering also runs smoothly at 60+ fps at full HD resolution now. Also worth a note: The raycasting method is updated to allow octrees greater than 16 levels - the scene below is created in an 18 level octree. Now, problems with precision begin to arise, which need to be solved.

Dienstag, 13. Mai 2014

Quadric Mesh Simplification with Source Code

In the past days I have written a quadric based mesh simplification program. After searching the internet I couldnt find any code that was free to use, not unnecessarily bloated, fast and memory efficient, even the quadric based method is soon 20 years old. I therefore decided to write one myself.

Features / Summary:
  • Threshold based, therefore faster than sorting based methods
  • Since the Quadric Matrices are symmetric, only 10 elements are stored & computed per Matrix instead of 16
  • Non-closed meshes are supported by extra treating mesh borders
  • Simplifies 2.000.000 triangles to 20.000 triangles in 3 seconds on a Core i7
  • MIT License
  • MS Visual Studio 2012 , C++
Update Sept.20th 2014 : improved quality of reduced borders

The result is short and easy to use in case you need to adopt it to your project. You can fetch the C++ Project with source here: (about 300 lines for the main part, contained in Simplify.h )

Download Source and Data

The code is about 4x-7x faster than Meshlab, which is already fast. Using multi-core programming, it could even be faster.

Here a comparison along Meshlab, QSlim and this method:

Program output (left) and Meshlab (right). Note that Meshlab produces floating teeth and looses details around the eyes, nose and the mouth region. Reduction was 85k -> 3k Triangles.

Original (left) this code (middle) and meshlab (right)

Here another comparison: Program output (left) and Meshlab (right).

Samstag, 3. Mai 2014

Raycaster Speed-Up up to 400% by Image Warping (ReProjection)

Introduction: Since real-time raytracing is getting faster like with the Brigade Raytracer e.g., I believe this technology can be an important contribution to this area, as it might bring raytracing one step closer to being usable for video games.

Algorithm: A technology I am working on since a while now is to exploit temporal coherence between two consecutive rendered images to speed up ray-casting. The idea is to store the x- y- and z-coordinate for each pixel in the scene in a coordinate-buffer and re-project it into the following screen using the differential view matrix. The resulting image will look as Fig.1.

The method then gathers empty 2x2 pixel blocks on the screen and stores them into an indexbuffer for raycasting the holes. Raycasting single pixels too inefficient. Small holes remaining after the hole-filling pass are closed by a simple image filter. To improve the overall quality, the method updates the screen in tiles (8x4) by raycasting an entire tile and overwriting the cache. Doing so, the entire cache is refreshed after 32 frames. Further, a triple buffer system is used. That means two image caches which are copied to alternately and one buffer that is written to. This is done since it often happens that a pixel is overwritten in one frame, but becomes visible already in the next frame. Therefore, before the hole filling starts, the two cache buffers are projected to the main image buffer.

Limitations: The method also comes with limitations of course. So the speed up depends on the motion in the scene obviously, and the method is only suitable for primary rays and pixel properties that remain constant over multiple frames, such as static ambient lighting. Further, during fast motions, the silhouettes of geometry close to the camera tends to loose precision and geometry in the background will not move as smooth as if the scene is fully raytraced each time. There, future work might include creating suitable image filters to avoid these effects.

Results: Most of the pixels can be re-used using this technology. As only a fraction of the original needs to be raycasted, the speed up is significant and up to 5x the original speed, depending on the scene (see Fig.2 - Fig.4). Resolution for that test was 1024x768, the GPU was an NVIDIA GeForce GTX765M.

Here also two videos showing this technology in action: Video1 Video2 
(I uploaded them a while ago)

Finally a few papers for further reading:
Exploiting Temporal Coherence in Ray Casted Walkthroughs
Iterative Image Warping
A Shared-Scene-Graph Image-Warping Architecture for VR: Low Latency versus Image Quality
Three-Dimensional Image Warping on Programmable Graphics Hardware
Accelerating Real-Time Shading with Reverse Reprojection Caching

Fig.1 Result after basic re-projection

Fig.2 Original Version

Fig.3 With Re-Projection Enabled + In Motion

Fig.4 With Re-Projection Enabled + Standing