Micro-Polygon vs. Texture Map Debate

CS348c - Computer Graphics Architectures

June 4, 1996

Overview of Micro-Polygon and Texture Mapping Techniques

Micro-Polygons and Texture Mapping are two techniques for providing detail in 3d Computer Graphics. In the micro-polygon approach, the scene is composed of many small polygons, each of which will project to one screen space pixel or less. This composition could be either at the modeling level, or a scene can be decomposed to micro-polygons as part of the rendering phase. In texture mapping multi-pixel polygons are used, but complex images are mapped onto their surfaces to give the appearance of extra complexity. The two techniques together define a spectrum of rendering styles, from a QuickTime VR type system where the entire scene is essentially one polygon with an image mapped onto it, all the way to the point where there are many sub-pixel polygons each of which essentially has a one pixel texture map.

For the purposes of this debate, however, we will consider micro-polygon to refer to 2-pixel or smaller sized polygons, and texture mapping to refer to Reality Engine style rendering, with triangles in the 25+ pixel size range.

Suggested Reading

So far there are two papers for the debate:

Debate Structure

The benefits and/or disadvantages of the two techniques will be debated around the following issues:

Overview Slides

Here are the overview slides for the debate (by Brad Johanson).

Micro-Polygons:

General Concessions:

Micropolygon's advantages lie in rendering scenes of large complexity and high resolution. I will concede that in situations of numerous large polygons and low complexity the Micropolgon way does not fair well.

However, the trends are the following:

  1. Larger scene complexity Computing power combined with consumer expectations is pushing up the bar in terms of what is "acceptable" image quality - which is a direct factor of scene complexity.
  2. Decreased polygon size Triangles size used to be assumed that it was 100 pixels. Currently, triangles are assumed to be around 25 pixels in size. The Micropolygon approach uses polygons between 1/2 pixel and 2 pixels large.

Remember that when comparing the two systems in Economics you must consider detail/performance vs. cost. Saying a Texture Mapped system is faster if it is of lower detail is meaningless.

Thus, it is my contention that as scene complexity continues to increase and polygon size decreases, the advantages of using Micropolygons will severely outweigh the "traditional" R.E. style polygon based texture map.

Economic and Architectural Issues, Mike Schroepfer

  1. One look into the architecture of the R.E. or IR shows that a large multitude of the work involved is used in the rasterization process (80 processors per board) - as compared to 8- 12 geometry processors for the entire system.
  2. Much of this work involves texturing - But since you are texturing first, in object coordinates if you use pre-filtered mit-mapped textures no filtering or interpolation is needed.
  3. Everything is essentially broken down into the same elements - the Micropolygon. This could simply hardware.
  4. Takes advantage of locality both in textures and in geometry

    This is an extreme advantage because low cost systems often skimp on memory (DRAM based PC graphics boards). Even on high-end systems it is much easier to get high performance out of serial memory accesses rather than random one
What is currently Lacking in the Micropolygon Approach

Not nearly as much development time has been put into hardware specialized to run these algorithms.

1. A hardware dicer

2. Methods to deal with the variety of higher level primitives.

The I.R. took longer with more effort than the R.E. It appears that we may have to think in a new paradigm in order to continue the rapid advance of graphic processing power. The simplicity of the back end of the Micropolygon approach seems a possible way to do this.

Mike's Slides

Performance and Detail Issues, David Redkey

Micropolygons out-perform standard hardware texture-mapping and generate better images too!

  1. Detailed geometry is the only way to capture appropriate occlusion and perspective distortion in realistic scenes. As Michael Deering concludes in "Where do all the Triangles go", increasing numbers of small polygons are needed to match the demand for realism.
  2. Micropolygons allow a clean framework for displacement maps and curved surfaces, which will become prevalent in the future.
  3. Micropolygons allow for reduced super-sampling. As shading models become more complex, the ratio of the costs of vertex transformation to sample shading goes down, making the micropolygon approach more desirable.
  4. By designing hardware that focuses only on gouraud shading during rasterization, we can certainly design faster rasterizers.
  5. Triangle bandwidth need not be a constraining factor if modern software visibility techniques are employed.

David's Micropolygon Slide David's Performance Slide

Texture Maps:

Economic and Architectural Issues, Brien Oberstein

Economics

Architectural Complexity

Performance and Detail Issues, Li-Yi Wei

Texture mapping and micropolygons are 2 way to capture realism. Basically texture mapping is more hacking because it tries to capture the local and global shading of objects via some cheaper way and at the same time produce convincing pictures. The benefits for texture mapping compared to micropolygons are :

  1. it's cheaper in terms of triangle bandwidth
  2. it's suitable for random access textures
  3. in applications that most objest are far away and are flat, texture mapping is good enough, like flight simulator and Doom. Micropolygons can give us better detail but at the expense of a large amount of tiny triangles and also unsuitable for RATs.

PostScript of Debate Overhead for Texture Performance and Detail: tex_perf.ps

This page created by:
Brad Johanson
bjohanso@graphics.stanford.edu