blob: 1f9e5bbe93b99277ae63761ce926463bdf81f1db [file] [log] [blame]
Name Strings
Date: 3/1/1999 Version: 1.5
WGL_EXT_extensions_string is required.
The association of a separate "read" and "draw" DC with the current
context allows for preprocessing of image data in an "off screen"
DC which is then read into a visible DC for final display.
New Procedures and Functions
BOOL wglMakeContextCurrentEXT(HDC hDrawDC,
HDC hReadDC,
HGLRC hglrc);
HDC wglGetCurrentReadDCEXT(VOID);
New Tokens
Returned by GetLastError (when wglMakeContextCurrentEXT fails):
Additions to Chapter 2 of the 1.2 GL Specification (OpenGL Operation)
Additions to Chapter 3 of the 1.2 GL Specification (Rasterization)
Additions to Chapter 4 of the 1.2 Specification (Per-Fragment Operations
and the Frame buffer)
[The following restriction is added to the end of the introductory
paragraph of section 4.2.4]
Accumulation operations are only allowed when the device context used
for reading is identical to the device context used for drawing.
[The list of error conditions at the end of section 4.2.4]
If there is no accumulation buffer, or the GL is in color index mode,
or if the read device context and the draw device context are not
identical, Accum generates the error INVALID_OPERATION.
Additions to Chapter 5 of the 1.2 Specification (Special Functions)
Additions to Chapter 6 of the 1.2 Specification (State and State Requests)
Additions to the WGL specification
The function wglMakeContextCurrentEXT associates the context <hglrc>
with the device <hDrawDC> for draws and the device <hReadDC> for
reads. All subsequent OpenGL calls made by the calling thread are
drawn on the device identified by <hDrawDC> and read on the device
identified by <hReadDC>.
The <hDrawDC> and <hReadDC> parameters must refer to drawing surfaces
supported by OpenGL. These parameters need not be the same <hdc>
that was passed to wglCreateContext when <hglrc> was created.
<hDrawDC> must have the same pixel format and be created on the
same device as the <hdc> that was passed into wlgCreateContext.
<hReadDC> must be created on the same device as the <hdc> that was
passed to wglCreateContext and it must support the same pixel type
as the pixel format of the <hdc> that was passed to wglCreateContext.
If wglMakeContextCurrentEXT is used to associate a different device
for reads than for draws, the "read" device will be used for the
following OpenGL operations:
1. Any pixel data that are sourced based on the value of READ_BUFFER.
Note, that accumulation operations use the value of READ_BUFFER,
but are not allowed when a different rendering context is used
for reads.
2. Any depth values that are retrieved by glReadPixels, glCopyPixels,
or any OpenGL extension that sources depth images from the frame
buffer in the manner of glReadPixels and glCopyPixels.
3. Any stencil values that are retrieved by glReadPixels, glCopyPixels,
or any OpenGL extension that sources stencil images from the frame
buffer in the manner of glReadPixels and glCopyPixels.
These frame buffer values are taken from the surface associated with
the device context specified by <hReadDC>.
No error will be generated if the value of READ_BUFFER at the time the
wglMakeContextCurrentEXT call is made does not correspond to a valid color
buffer in <hReadDC>. Also, no error due to READ_BUFFER mismatch will be
generated by subsequent calls to any of the operations enumerated
above, but the pixels values used will be undefined until READ_BUFFER
is set to a color buffer that is valid in the <hReadDC>. Operations that
query the value of READ_BUFFER (i.e., glGet, glPushAttrib) use the
value set last in the context, independent of whether it is a valid
buffer in <hReadDC>.
Error conditions set by glReadBuffer (even when called implicitly via
glPopAttrib) and by the operations enumerated above are with respect
to color and ancillary buffers available in <hReadDC> (i.e.,
glReadBuffer(GL_BACK_BUFFER) will generate an error when <hReadDC> is
single buffered, and so will an operation that tries to source stencil
images when <hReadDC> does not have a stencil buffer).
If wglMakeContextCurrentEXT succeeds, the return value is TRUE. If
the function fails, the return value is FALSE. To get extended error
information, call GetLastError. Possible errors are as follows:
ERROR_INVALID_PIXEL_FORMAT The pixel format associated with
<hDrawDC> does not match the pixel
format associated with the render
ERROR_INVALID_PIXEL_TYPE_EXT The pixel type for <hReadDC> is
different than the pixel type
associated with the <hdc> that was
passed to wglCreateContext.
ERROR_DC_NOT_FOUND <hReadDC> or <hDrawDC> is not a valid
device context.
ERROR_NO_SYSTEM_RESOURCES The device contexts specified by
<hReadDC> and <hDrawDC> cannot exist
in the framebuffer simultaneously.
wglGetCurrentReadDC returns a handle to the "read" device context that
is associated with the current OpenGL rendering context of the calling
thread. If the calling thread does not have a current context, the
return value is NULL.
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 is not a GL extension, it is not included in the
New State
New Implementation Dependent State