System Support for OpenGL Direct Rendering

Mark J. Kilgard David Blythe Deanna Hohn
Silicon Graphics, Inc.
2011 N. Shoreline
Mountain View, CA 94043-1389
email: mjk@sgi.com blythe@sgi.com hohn@sgi.com

Published in the
Proceedings of Graphics Interface '95
May 1995
Quebec City, Quebec

Abstract

OpenGL's window system support for the X Window System explicitly allows implementations to support direct rendering of OpenGL commands to the graphics hardware. Rendering directly to the hardware avoids the overhead of packing and relaying protocol requests to the X server inherent in indirect rendering.

The OpenGL implementation available for Silicon Graphics workstations supports direct rendering using virtualizable graphics hardware in conjunction with the kernel and the X server. The techniques described provide ``maximum performance'' rendering for OpenGL. Some of the issues are specific to OpenGL, but most of the techniques described are appropriate for the implementation of any high-performance direct rendering graphics interface.

Keywords: OpenGL, Virtual Graphics, Direct Rendering.

• 1 Introduction
• 2 Background
  • 2.1 Direct Rendering Benefits
  • 2.2 ``Maximum Performance'' 3D Rendering
  • 2.3 Virtual Graphics
  • 2.4 SGI-style Graphics Hardware
    • 2.4.1 Virtualized, Direct Rendering Needs
    • 2.4.2 Window Clipping Hardware
    • 2.4.3 Display Mode Support
  • 2.5 Previous IRIS GL Support
  • 2.6 Other Approaches
• 3 OpenGL Requirements
  • 3.1 Context Model
  • 3.2 Sharing of Window State
  • 3.3 Per Window Double Buffering
• 4 Virtualizing SGI Graphics
  • 4.1 Making Current to a Window
  • 4.2 Context Switching
  • 4.3 Clip Validation
  • 4.4 Fast Buffer Swaps
  • 4.5 Window Display Mode Validation
  • 4.6 Shared Software Buffers
  • 4.7 Cursors
• 5 Other Issues
  • 5.1 Overlays and Underlays
  • 5.2 Synchronization Issues
  • 5.3 Correct Front Buffer Rendering for X
  • 5.4 X Server Multi-rendering for Indirect Rendering
• Acknowledgments
• References
• About this document ...