CIS 788A Advanced Compositing, Texturing and Volume Rendering

Lab 1 (Option 2): Rendering Glass: Specular Highlights, Texture Mapping and Transparency in OpenGL

Objectives

This will be a short and simple lab to examine issues associated with rendering correct opacity and specular highlights using OpenGL and programmable shader capabilities. We will assume a constant colored background and ignore any refractions in the glass, however, test your results on constant as well as non-constant backgrounds to better analyze the compositing. New features in OpenGL 1.4 allow for a separate specular color to be carried forward until after texture sampling, however, the interaction between this and textures having an opacity channel need to be examined. Correct compositing requires a front-to-back or back-to-front sorting of the graphics primitives. We will look at the many possible ways to achieve correct opacity accumulation and the precision issues in modern graphics GPU's. Examine the various blending formulas and operations to achieve special effects. In short, play with blending, play with specular highlights and play with textures (in particular, non-decal textures).

Tasks

• Develop a program that will read in a object file (OBJ, DXF, etc.) and an associate texture map / atlas.
• Your program should have the familiar set of user interactions, rotate, translate, zoom
• Add a user interface to place point light sources or spotlights on a sphere surrounding your object.
• Research the Separate specular functionality of OpenGL.
• Experiment with the various blending operators and factors.
• Try to determine a new method for handling the opacity near silhouette edges

Ideas

• Try using Pixel Masks via textures and an alpha test to get specular highlights on the opaque regions only.
• Use environment mapping with an opacity texture to make the edges of the glass more opaque.
• Use fin textures (aka from shell and fin rendering) to add more opacity near the silhouettes.
• Consider using the GL_MIN or GL_MAX blending modes to shade silhouette edges (for opaque objects), by playing with the lighting and material properties.

Results

Last Modified by Roger Crawfis, April 5, 2004