extensions/EXT/WGL_EXT_swap_control.txt

Name

    EXT_swap_control

Name Strings

    WGL_EXT_swap_control

Version

    Date: 9/23/1999   Revision: 1.5

Number

    172

Dependencies

    WGL_EXT_extensions_string is required.

Overview

    This extension allows an application to specify a minimum periodicity
    of color buffer swaps, measured in video frame periods.

New Procedures and Functions

    BOOL wglSwapIntervalEXT(int interval)

    int wglGetSwapIntervalEXT(void)

New Tokens

    None

Additions to Chapter 2 of the 1.2 GL Specification (OpenGL Operation)

    None

Additions to Chapter 3 of the 1.2 GL Specification (Rasterization)

    None

Additions to Chapter 4 of the 1.2 GL Specification (Per-Fragment Operations
and the Framebuffer)

    None

Additions to Chapter 5 of the 1.2 GL Specification (Special Functions)

    None

Additions to Chapter 6 of the 1.2 GL Specification (State and State Requests)

    None

Additions to the WGL Specification

    wglSwapIntervalEXT specifies the minimum number of video frame periods
    per buffer swap for the window associated with the current context.
    The interval takes effect when SwapBuffers or wglSwapLayerBuffer
    is first called subsequent to the wglSwapIntervalEXT call.

    The parameter <interval> specifies the minimum number of video frames
    that are displayed before a buffer swap will occur.

    A video frame period is the time required by the monitor to display a 
    full frame of video data.  In the case of an interlaced monitor,
    this is typically the time required to display both the even and odd 
    fields of a frame of video data.  An interval set to a value of 2
    means that the color buffers will be swapped at most every other video
    frame.

    If <interval> is set to a value of 0, buffer swaps are not synchron-
    ized to a video frame.  The <interval> value is silently clamped to
    the maximum implementation-dependent value supported before being
    stored.

    The swap interval is not part of the render context state.  It cannot
    be pushed or popped.  The current swap interval for the window
    associated with the current context can be obtained by calling
    wglGetSwapIntervalEXT.  The default swap interval is 1.

Dependencies on WGL_EXT_extensions_string

    Because there is no way to extend wgl, these calls are defined in
    the ICD and can be called by obtaining the address with
    wglGetProcAddress.  Because this extension is a WGL extension, it
    is not included in the GL_EXTENSIONS string.  Its existence can be
    determined with the WGL_EXT_extensions_string extension.

    For historical reasons, GL_EXT_SWAP_CONTROL is also included in the
    GL_EXTENSIONS string as return from glGetString.

Errors

    If the function succeeds, the return value is TRUE. If the function
    fails, the return value is FALSE.  To get extended error information,
    call GetLastError.

       ERROR_INVALID_DATA      The <interval> parameter is negative.

       ERROR_DC_NOT_FOUND      An RC was not current to the calling
                               thread; therefore, no DC could be
                               obtained.

New State

    None

New Implementation Dependent State

    None