Procedural Graphics with DirectX 11

1. Procedural Graphics with DirectX 11 James Reid

2. Meshes • A mesh is what all the textures are laid on. • Meshes are deformed to give us the nice terrains seen in games today using height maps or procedural methods. • More vertices require more GPU power! • Goal: reduce number of vertices in a mesh without sacrificing quality.

3. Height Maps • Advantages: • Easily modeled by an artist. • Easily implemented. • Normal maps can be paired for lighting. • Use far less memory than meshes. • Easier on the CPU/GPU. • Disadvantages: • Only able to show 256 distinct heights in grayscale. • Can quickly consume hard disk space when having to store height/normal/tangent/etc maps. • Image: The Elder Scrolls V: Skyrim

4. What is Procedural? • From Wikipedia: “content generated algorithmically rather than manually” • Content is created at run time, not compile time or stored in file. • Most games use height maps and models. • Image: The Elder Scrolls III: Morrowind

5. Why Use Procedural? • Memory usage is far less on both the hard disk and in RAM. • Size limitations are much larger than those involving height maps. • Allows games to be released on a single CD/DVD. • Makes downloadable games more manageable. • Image: Minecraft

6. Basis For Procedural • Noise algorithms. • Perlin • Voronoi • Can be implemented in different dimensions. • 1D • 2D (used for terrain/clouds) • 3D (used for clouds the user can fly through)

9. How Noise Works • Summing up of static maps generated with pseudorandom numbers. • Basic Algorithm: double t = 0; double amplitude = 1; double freq = m_dFrequency; for(inti = 0; i < m_nOctaves; i++) { t += GetValue(x * freq + m_nSeed, y * freq + m_nSeed) * amplitude; amplitude *= m_dPersistence; freq *= 2; } return t;

11. Using Perlin Noise • Start with a mesh. • Generate a height field using Perlin Noise. • Assign the coordinate for each pair in the mesh. • Result:

12. Scalability • Makes very convincing terrain. • Issues: • High number of vertices. • Static meshes can’t adapt to camera’s view. • Solution: • Use a quadtree structure to store the data.

13. Quadtree Structure • Similar to binary trees, but has 4 nodes instead of 2.

14. Quadtree Mesh

15. Uses For The Quadtree • View frustum culling. • Level of detail (LOD). • Collision detection. • Grid location. • Reducing total vertices.

16. View Frustum • Field of view the camera has. • Used in culling and LOD.

17. Frustum Culling • Removing of primitives that are not seen from the graphics pipeline to increase performance. • More types: • Backface • Contribution • Occlusion

19. Level of Detail (LOD) • The amount of detail shown being based on the camera’s view point. • Where DirectX 11 makes a difference. • Use of the geometry shader.

21. Vertex Interpolation Error • When changing LOD the new vertices may cause popping. • Several solutions to this, most common is to just take the midpoint of both vertices.

22. Texture Morphing • LOD can cause textures to not line up and varying levels of detail. • Solution: Use texture blending to hide the effect.

23. Vertex Reduction • Use minimum number of vertices based on slope of terrain. • Image: Shamus Young (Twenty Sided) • Top right: no optimization • Bottom left: optimized grid, removed about two-thirds of total vertices (Huge performance increase!)

24. Tessellation • Started in DirectX 10 – can be controlled by user with DirectX 11 • Take a mesh and add more primitives to smooth it out.

26. Putting It All Together • Use CPU to determine LOD and any culling to be done based on view frustum. • Use noise algorithm in real time on the GPU to generate height field. • Remove any unwanted vertices based on slope of terrain (e.g. flat areas will use two triangles instead of filling up the mesh). • Morph the textures at the LOD breaks. • Tessellate the mesh in high detail locations.

27. Examples • http://www.youtube.com/watch?v=rL8zDgTlXso • Start at 3:20 • http://www.youtube.com/watch?annotation_id=annotation_790483&feature=iv&src_vid=OiGADgezjC8&v=oUSdSjnDB_E • Start at 0:49 • http://www.youtube.com/watch?v=uzXB0m3_MHQ • Start at 0:25

28. References • Schneider, J., & Westermann, R. (2006). Gpu-friendly high-quality terrain rendering., Computer Graphics and Visualization Group, TechnischeUniversitätMünchen, Munich, Germany. • Yusov, E., & Turlapov, V. (2007). Gpu-optimized efficient quad-tree based progressive multiresolution model for interactive large scale terrain rendering., Department of Computational Mathematics and Cybernetics, Nizhny Novgorod State University, Nizhny Novgorod, Russia. • Perlin, K. (2001). Improving noise., Media Research Laboratory, Dept. of Computer Science, New York University , New York City, NY, . • Verts, W. T., & Hill, Jr., F. S. (1989). Quadtree meshes, COINS Department, ECE Department, University of Massachusetts, Amherst, MA, . • Olsen, J. (2004). Realtime procedural terrain generation., Department of Mathematics And Computer Science (IMADA), University of Southern Denmark, . • Bernhardt, A., Maximo, A., Velho, L., Hnaidi, H., & Cani, M. (2011). Real-time terrain modeling using cpu–gpu coupled computation., INRIA, Grenoble Univ., Univ. Lyon 1, IMPA, France, Brazil.