# Environment Variables

Mesa supports the following environment variables:

- MESA_NO_ASM - if set, disables all assembly language optimizations
- MESA_NO_MMX - if set, disables Intel MMX optimizations
- MESA_NO_3DNOW - if set, disables AMD 3DNow! optimizations
- MESA_NO_SSE - if set, disables Intel SSE optimizations
- MESA_DEBUG - if set, error messages are printed to stderr. If the value of MESA_DEBUG is "FP" floating point arithmetic errors will generate exceptions.
- MESA_NO_DITHER - if set, disables dithering, overriding glEnable(GL_DITHER)
- MESA_TEX_PROG - if set, implement conventional texture env modes with fragment programs (intended for developers only)
- MESA_TNL_PROG - if set, implement conventional vertex transformation operations with vertex programs (intended for developers only). Setting this variable automatically sets the MESA_TEX_PROG variable as well.
- MESA_EXTENSION_OVERRIDE - can be used to enable/disable extensions. A value such as "GL_EXT_foo -GL_EXT_bar" will enable the GL_EXT_foo extension and disable the GL_EXT_bar extension.
- MESA_GLSL - shading language options

The following are only applicable to the Xlib software driver. See the Xlib software driver page for details.

- MESA_RGB_VISUAL - specifies the X visual and depth for RGB mode
- MESA_CI_VISUAL - specifies the X visual and depth for CI mode
- MESA_BACK_BUFFER - specifies how to implement the back color buffer, either "pixmap" or "ximage"
- MESA_GAMMA - gamma correction coefficients for red, green, blue channels
- MESA_XSYNC - enable synchronous X behavior (for debugging only)
- MESA_GLX_FORCE_CI - if set, force GLX to treat 8bpp visuals as CI visuals
- MESA_GLX_FX - set to either "fullscreen" for full-screen rendering, "window" to render into a window, or "disable" to disable the Glide driver.
- MESA_GLX_FORCE_ALPHA - if set, forces RGB windows to have an alpha channel.
- MESA_GLX_DEPTH_BITS - specifies default number of bits for depth buffer.
- MESA_GLX_ALPHA_BITS - specifies default number of bits for alpha channel.