Week 13 - Monday Radiosity Ray tracing Precomputed lighting - PowerPoint PPT Presentation

Week 13 - Monday

 Radiosity  Ray tracing  Precomputed lighting  Precomputed occlusion

 We can imagine all the different rendering techniques as sitting on a spectrum reaching from purely appearance based to purely physically based Sprites Billboards Appearance Physically Based Based Layers Triangles Lightfields Global illumination

 When objects are close to the viewer, small changes in viewing location can have big effects  When objects are far away, the effect is much smaller  As you know by now, a skybox is a large mesh containing the entire scene  Some skyboxes look crappy because there isn't enough resolution screen resolution  Minimum texture resolution (per cube face) = tan(fov/2)

 If you're trying to recreate a complex scene from reality, you can take millions of pictures of it from many possible angles  Then, you can use interpolation and warping techniques to stitch them together  Huge data storage requirements  Each photograph must be catalogued based on location and orientation  High realism output!  Remember the video with the robot and the omnidirectional camera

 A sprite is an image that moves around the screen  Sprites were the basis of most old 2D video games (back when those existed, before the advent of Flash)  By putting sprites in layers, it is possible to make a compelling scene  Sequencing sprites can achieve animation

 Applying sprites to 3D gives billboarding  Billboarding is orienting a textured polygon based on view direction  Billboarding can be effective for objects without solid surfaces  Vegetation  Smoke  Fire  Each polygon (thought of as a quadrilateral, even if often two triangles in practice) needs a surface normal n and an up vector u  A billboard also has an anchor location as a point of reference

 A screen-aligned billboard is one that sits on the screen  The u vector comes from the camera  The n vector is the negation of the camera's view vector  MonoGame handles all of this for you in the SpriteBatch class, of course

 If the object is supposed to exist in the world, it needs to change as the world changes  The world has some implied up vector that can be used to derive an appropriate up vector (and thereby rotation matrix) for the sprites  For small sprites (such as particles) the billboard's surface normal can be the negation of the view plane normal  Larger sprites should have different normals that point the billboard directly at the viewpoint

 Many (sometimes hundreds) of billboards can be put together to make smoke or fire effects  A small set of billboards can be drawn many times with different scaling and rotation factors and overlapped  Issues can happen if these billboards intersect with objects  Soft particles is a technique for lowering the opacity of billboards when they are close to "real" objects

 Axial billboards are another common technique  In axial billboards, a polygon rotates around some world space axis and tries to face the viewer as much as is allowed  This technique is useful for trees viewed from a distance  Like cross trees, the illusion is ruined if the viewer moves too high  Some implementations may switch between the impostor billboard and a real model if the viewer gets close enough  It works for laser beams too

In a particle system, many small, separate objects are controlled using some algorithm  Applications:   Fire  Smoke  Explosions  Water Particle systems refer more to the animation than to the rendering  Particles can be points or lines or billboards  Modern GPUs can generate and render particles in hardware 

 Image processing  Tone mapping  HDR lighting  Lens flare  Bloom

 Keep working on Assignment 4  Due Friday by midnight  Keep working on Project 3  Keep reading Chapter 10