xref: /third_party/openGLES/extensions/EXT/GLX_EXT_texture_from_pixmap.txt

Name

    EXT_texture_from_pixmap

Name Strings

    GLX_EXT_texture_from_pixmap

Contributors

    James Jones, NVIDIA
    Aaron Plattner, NVIDIA
    Andy Ritger, NVIDIA

Contact

    David Reveman, Novell, Inc. (davidr 'at' novell.com)

Status

    Complete

Version

    17 (10 Feb 2009)

Number

    344

Dependencies

    OpenGL 1.1 is required.
    GLX 1.3 is required.
    GL_EXT_framebuffer_object affects the definition of this extension.
    GL_ARB_texture_rectangle affects the definition of this extension.
    GL_ARB_texture_non_power_of_two affects the definition of this extension.
    GL_SGIS_generate_mipmap affects the definition of this extension.

Overview

    This extension allows a color buffer to be used for both rendering and
    texturing.

    Only color buffers of pixmaps can be used for texturing by this extension
    but other types of drawables can be supported by future extensions layered
    on top of this extension.

    The functionality of this extension is similar to WGL_ARB_render_texture. 
    However, the purpose of this extension is not to provide
    "render to texture" like functionality but rather the ability to bind
    an existing X drawable to a texture. Though, there is nothing that
    prohibits it from being used for "render to texture".

    -   Windows are problematic as they can change size and therefore are not
        supported by this extension.

    -   Only a color buffer of a GLX pixmap created using an FBConfig with
        attribute GLX_BIND_TO_TEXTURE_RGB_EXT or GLX_BIND_TO_TEXTURE_RGBA_EXT
        set to TRUE can be bound as a texture.

    -   The texture internal format is determined when the color buffer
        is associated with the texture, guaranteeing that the color 
        buffer format is equivalent to the texture internal format.

    -   A client can create a complete set of mipmap images if
        EXT_framebuffer_object is supported.


IP Status 

    There are no known IP issues. 

Issues

    1. What should this extension be called?

    Even though it is very similar to WGL_ARB_render_texture that name is
    not appropriate as the intention of this extension is not
    "render to texture" like functionality.

    EXT_texture_from_pixmap seams most appropriate. Layering of future
    extensions on top of this extension for using other type of drawables
    as textures follows the same conventions as vertex/pixel buffer objects
    and vertex/fragment programs.


    2. Should we allow applications to render to different mipmap levels and
    cube map faces?

    In order to discourage the use of this extension as a render to texture
    mechanism, cube maps and rendering directly to mip-map levels > 0 will
    not be supported.  A new FBConfig attribute is introduced that specifies
    whether or not drawables created with that config will support multiple
    mipmap levels when bound to a texture.  The other mipmap levels can be
    filled in by the EXT_framebuffer_object GenerateMipmapEXT function.

    Specifying which level of a pixmap was being rendered to on a per-drawable
    basis, as was done in the WGL_ARB_render_texture extension, also
    introduces concurrency issues.  The state of the drawable when it was
    being rendered two by two separate threads of execution and both were
    changing the mipmap level was difficult to define.

    It is also desireable to keep this extension as simple as possible.
    Adding functionality that complicates the implementation and that is not
    directly relevenat to the goal of exposing a mechanism for texturing from
    arbitrary X pixmaps is not productive.  If the ability to render directly
    to all levels of a texture is needed, EXT_framebuffer_object is the
    extension that should be used.


    3. Should 1D textures be supported?

    X servers layered on top of an OpenGL implementation might not be able
    to support this.  A new FBConfig attribute is introduced specifying
    which texture targets a drawable created with the given FBConfig can
    be bound to.


    4. What should the default value for GLX_TEXTURE_TARGET_EXT be?  Should
    users be required to set this value if GLX_TEXTURE_FORMAT_EXT is not
    GLX_TEXTURE_FORMAT_NONE_EXT?

    The implementation is capable of choosing a reasonable default, we simply
    need to specify the correct way to do so.  We can base the ordering on
    the properties of the pixmap and the texturing capabilities of the
    pixmap's FBConfig and the implementation.

    The order is:

    - If GL_ARB_texture_non_power_of_two is supported GL_TEXTURE_2D will
      be used for all pixmap sizes.

    - If only GL_ARB_texture_rectangle is supported GL_TEXTURE_2D will
      be used for all power of two pixmap sizes and GL_TEXTURE_RECTANGLE_ARB
      will be used for all non power of two pixmap sizes.


    5. Should users be required to re-bind the drawable to a texture after
    the drawable has been rendered to?

    It is difficult to define what the contents of the texture would be if
    we don't require this.  Also, requiring this would allow implementations
    to perform an implicit copy at this point if they could not support
    texturing directly out of renderable memory.

    The problem with defining the contents of the texture after rendering
    has occured to the associated drawable is that there is no way to
    synchronize the use of the buffer as a source and as a destination.
    Direct OpenGL rendering is not necessarily done in the same command
    stream as X rendering.  At the time the pixmap is used as the source
    for a texturing operation, it could be in a state halfway through a
    copyarea operation in which half of it is say, white, and half is the
    result of the copyarea operation.  How is this defined?  Worse, some
    other OpenGL application could be halfway through a frame of rendering
    when the composite manager sources from it.  The buffer might just
    contain the results of a "glClear" operation at that point.

    To gurantee tear-free rendering, a composite manager would run as follows:

    -receive request for compositing:
    XGrabServer()
    glXWaitX() or XSync()
    glXBindTexImageEXT()

    <Do rendering/compositing>

    glXReleaseTexImageEXT()
    XUngrabServer()

    Apps that don't synchronize like this would get what's available, 
    and that may or may not be what they expect.


    6. What is the result of calling GenerateMipmapEXT on a drawable that
    was not created with mipmap levels?

    The results are undefined.


    7. Rendering done by the window system may be y-inverted compared
    to the standard OpenGL texture representation.  More specifically:
    the X Window system uses a coordinate system where the origin is in
    the upper left; however, the GL uses a coordinate system where the
    origin is in the lower left.  Should we define the contents of the
    texture as the y-inverted contents of the drawable?

    X implementations may represent their drawables differently internally,
    so y-inversion should be exposed as an FBConfig attribute.
    Applications will need to query this attribute and adjust their rendering
    appropriately.

    If a drawables is y-inverted and is bound to a texture, the contents of the
    texture will be y-inverted with respect to the standard GL memory layout.
    This means the contents of a pixmap of size (width, height) at pixmap
    coordinate (x, y) will be at location (x, height-y-1) in the texture.
    Applications will need to adjust their texture coordinates accordingly to
    avoid drawing the texture contents upside down.


    8. Why wasn't this extension based on FBO instead of ARB_render_texture?
    Isn't the render_texture extension deprecated?

    At first glance, FBO may seem like the perfect framework to base a spec
    for texturing from pixmap surfaces on.  It replaced the
    WGL_ARB_render_texture specification, which provided a mechanism to
    texture from pbuffer surfaces.  However, this train of thought is another
    side effect of the unfortunate naming of the WGL_ARB_render_texture
    specification.  FBO and the orginal render_texture specification were
    two different solutions to the problem of how to render to and texture
    from the same surface.  WGL_ARB_render_texture provided a method to bind
    a texture to a drawable surface, as this extension does.  FBO provides the
    opposite solution, allowing rendering to arbitrary surfaces including
    textures.  In the case of FBO, the application doing the rendering knows
    that it needs to render to an alternate surface.  In our usage case, the
    application doing the rendering is arbitrary, and has no knowledge that another
    application wants to use the surface it is rendering to as a texture.  The
    only application able to name the surface is the one texturing from it.
    Therefore, it makes sense to provide a mechanism for binding a texture to
    an arbitrary surface in general, and a pixmap in this particular case.


    9. Why not allow binding directly to an X pixmap without creating an
    intermediate GLX pixmap?

    Architecturally, GLX has moved away from operating directly on X
    drawables.  This allows GLX specific attributes to be associated with the
    GLX drawables.  In this case, it is important to associate an FBConfig
    with the drawable.  The FBConfig contains attributes specifying the
    internal format the GL will use when utilizing the drawable's framebuffer
    as a texture.


New Procedures and Functions

    void glXBindTexImageEXT (Display     *display, 
                             GLXDrawable drawable, 
                             int         buffer,
                             const int   *attrib_list)

    void glXReleaseTexImageEXT (Display     *display, 
                                GLXDrawable drawable, 
                                int         buffer)


New Tokens

    Accepted by the <Attribute> parameter of glXGetFBConfigAttrib and 
    the <attrib_list> parameter of glXChooseFBConfig:

        GLX_BIND_TO_TEXTURE_RGB_EXT        0x20D0
        GLX_BIND_TO_TEXTURE_RGBA_EXT       0x20D1
        GLX_BIND_TO_MIPMAP_TEXTURE_EXT     0x20D2
        GLX_BIND_TO_TEXTURE_TARGETS_EXT    0x20D3
        GLX_Y_INVERTED_EXT                 0x20D4

    Accepted as an attribute in the <attrib_list> parameter of
    glXCreatePixmap, and by the <attribute> parameter of glXQueryDrawable:

        GLX_TEXTURE_FORMAT_EXT             0x20D5
        GLX_TEXTURE_TARGET_EXT             0x20D6
        GLX_MIPMAP_TEXTURE_EXT             0x20D7

    Accepted as a value in the <attrib_list> parameter of glXCreatePixmap
    and returned in the <value> parameter of glXQueryDrawable when
    <attribute> is GLX_TEXTURE_FORMAT_EXT:

        GLX_TEXTURE_FORMAT_NONE_EXT        0x20D8
        GLX_TEXTURE_FORMAT_RGB_EXT         0x20D9
        GLX_TEXTURE_FORMAT_RGBA_EXT        0x20DA

    Accepted as bits in the GLX_BIND_TO_TEXTURE_TARGETS_EXT variable:

        GLX_TEXTURE_1D_BIT_EXT             0x00000001
        GLX_TEXTURE_2D_BIT_EXT             0x00000002
        GLX_TEXTURE_RECTANGLE_BIT_EXT      0x00000004

    Accepted as a value in the <attrib_list> parameter of glXCreatePixmap
    and returned in the <value> parameter of glXQueryDrawable when
    <attribute> is GLX_TEXTURE_TARGET_EXT:

        GLX_TEXTURE_1D_EXT                 0x20DB
        GLX_TEXTURE_2D_EXT                 0x20DC
        GLX_TEXTURE_RECTANGLE_EXT          0x20DD

    Accepted by the <Buffer> parameter of glXBindTexImageEXT and 
    glXReleaseTexImageEXT: 

        GLX_FRONT_LEFT_EXT                 0x20DE
        GLX_FRONT_RIGHT_EXT                0x20DF
        GLX_BACK_LEFT_EXT                  0x20E0
        GLX_BACK_RIGHT_EXT                 0x20E1
        GLX_FRONT_EXT                      GLX_FRONT_LEFT_EXT
        GLX_BACK_EXT                       GLX_BACK_LEFT_EXT
        GLX_AUX0_EXT                       0x20E2
        GLX_AUX1_EXT                       0x20E3 
        GLX_AUX2_EXT                       0x20E4 
        GLX_AUX3_EXT                       0x20E5 
        GLX_AUX4_EXT                       0x20E6 
        GLX_AUX5_EXT                       0x20E7 
        GLX_AUX6_EXT                       0x20E8
        GLX_AUX7_EXT                       0x20E9 
        GLX_AUX8_EXT                       0x20EA 
        GLX_AUX9_EXT                       0x20EB


GLX Protocol

    Two new GLX protocol commands are added.

        BindTexImageEXT
            1           CARD8                   opcode (X assigned)
            1           16                      GLX opcode (glXVendorPrivate)
            2           6+n                     request length
            4           1330                    vendor specific opcode
            4           CARD32                  context tag
            4           GLX_DRAWABLE            drawable
            4           INT32                   buffer
            4           CARD32                  num_attributes
            4*n         LISTofATTRIBUTE_PAIR    attribute, value pairs.

        ReleaseTexImageEXT
            1           CARD8           opcode (X assigned)
            1           16              GLX opcode (glXVendorPrivate)
            2           5               request length
            4           1331            vendor specific opcode
            4           CARD32          context tag
            4           GLX_DRAWABLE    drawable
            4           INT32           buffer


Errors

Additions to Chapter 2 of the OpenGL 1.2.1 Specification (OpenGL Operation) 

    None. 

Additions to Chapter 3 of the OpenGL 1.2.1 Specification (Rasterization) 

    None. 

Additions to Chapter 4 of the OpenGL 1.2.1 Specification (Per-Fragment 
Operations and the Frame Buffer) 

    None. 

Additions to Chapter 5 of the OpenGL 1.2.1 Specification (Special Functions) 

    None. 

Additions to Chapter 6 of the OpenGL 1.2.1 Specification (State and State 
Requests) 

    None. 

Additions to the GLX Specification

    Add to table 3.1, GLXFBConfig Attributes:

    Attribute                       Type    Notes
    ------------------------------- ------- -------------------------------------------------------------------
    GLX_BIND_TO_TEXTURE_RGB_EXT     boolean True if color buffers can be bound to RGB texture
    GLX_BIND_TO_TEXTURE_RGBA_EXT    boolean True if color buffers can be bound to RGBA texture
    GLX_BIND_TO_MIPMAP_TEXTURE_EXT  boolean True if color buffers can be bound to textures with multiple levels
    GLX_BIND_TO_TEXTURE_TARGETS_EXT bitmask Bitmask of texture targets color buffers can be bound to
    GLX_Y_INVERTED_EXT              boolean True if the drawable's framebuffer is y-inverted.  This can be used to determine if y-inverted texture coordinates need to be used when texturing from this drawable when it is bound to a texture target.

    Additions to table 3.4, Default Match Criteria for GLXFBConfig attributes:

    Attribute                       Default              Selection Criteria Priority
    ------------------------------- -------------------- ------------------ ---------
    GLX_BIND_TO_TEXTURE_RGB_EXT     GLX_DONT_CARE        Exact
    GLX_BIND_TO_TEXTURE_RGBA_EXT    GLX_DONT_CARE        Exact
    GLX_BIND_TO_MIPMAP_TEXTURE_EXT  GLX_DONT_CARE        Exact
    GLX_BIND_TO_TEXTURE_TARGETS_EXT -                    Mask
    GLX_Y_INVERTED_EXT              GLX_DONT_CARE        Exact

    Modifications to 3.3.3, "Configuration Management"

    Add after paragraph 17 in the description of FBConfigs:

    GLX_Y_INVERTED_EXT is a boolean describing the memory layout used for
    drawables created with the GLXFBConfig.  The attribute is True if the
    drawable's framebuffer will be y-inverted.  This can be used to determine
    if y-inverted texture coordinates need to be used when texturing from this
    drawable when it is bound to a texture target.

    Modifications to 3.3.5, "Offscreen Rendering"

    Modify paragraph 3 of the description of glXCreatePixmap:

    <attrib_list> specifies a list of attributes for the pixmap.  The list has
    the same structure as described for glXChooseFBConfig.  Currently the
    following attributes can be specified in attrib_list:
    GLX_TEXTURE_FORMAT_EXT, GLX_TEXTURE_TARGET_EXT, GLX_MIPMAP_TEXTURE_EXT,
    attrib_list may be NULL or empty (first attribute of None), in which case
    all attributes assume their default values as described below.

    GLX_TEXTURE_FORMAT_EXT describes the texture format this pixmap can be
    bound to.  Valid values are GLX_TEXTURE_FORMAT_RGB_EXT,
    GLX_TEXTURE_FORMAT_RGBA_EXT, and GLX_TEXTURE_FORMAT_NONE_EXT.

    GLX_TEXTURE_TARGET_EXT can be set to GLX_TEXTURE_1D_EXT,
    GLX_TEXTURE_2D_EXT, or GLX_TEXTURE_RECTANGLE_EXT; it indicates the type
    of texture that will be created when GLX_TEXTURE_FORMAT_EXT is not
    GLX_TEXTURE_FORMAT_NONE_EXT.  The default value of GLX_TEXTURE_TARGET_EXT
    depends on the capabilities in <config> and the dimensions of the pixmap.
    If <config> has GLX_TEXTURE_2D_BIT set and one or more of the following is
    true:

        * GLX_TEXTURE_RECTANGLE_BIT_EXT is not set in <config>

        * GL_ARB_texture_non_power_of_two is supported

        * the pixmap's width and height are powers of 2

    the default value for GLX_TEXTURE_TARGET_EXT is GLX_TEXTURE_2D_EXT.

    Otherwise, the first supported target is chosen in this order:
    GLX_TEXTURE_RECTANGLE_EXT, GLX_TEXTURE_1D_EXT.

    GLX_MIPMAP_TEXTURE_EXT indicates that storage for mipmaps should be
    allocated.  Space for mipmaps will be set aside if GLX_TEXTURE_FORMAT_EXT
    is not GLX_TEXTURE_FORMAT_NONE_EXT and GLX_MIPMAP_TEXTURE_EXT is TRUE.
    The default value is FALSE.

    Modify paragraph 5 of the description of glXCreatePixmap:

    ...If <pixmap> is not a valid Pixmap XID, then a BadPixmap error is
    generated.  A BadConfig error is generated if any of the following
    conditions are true:

        * GLX_TEXTURE_FORMAT_EXT is GLX_TEXTURE_FORMAT_RGB_EXT and
          <config> does not have GLX_BIND_TO_TEXTURE_RGB set to TRUE.

        * GLX_TEXTURE_FORMAT_EXT is GLX_TEXTURE_FORMAT_RGBA_EXT and
          <config> does not have GLX_BIND_TO_TEXTURE_RGBA set to TRUE.

        * GLX_MIPMAP_TEXTURE_EXT is set to TRUE and <config> does not
          have GLX_BIND_TO_MIPMAP_EXT set to TRUE.

        * GLX_TEXTURE_TARGET_EXT is set to GLX_TEXTURE_1D_EXT
          and <config> does not have GLX_TEXTURE_1D_BIT_EXT set.

        * GLX_TEXTURE_TARGET_EXT is set to GLX_TEXTURE_2D_EXT
          and <config> does not have GLX_TEXTURE_2D_BIT_EXT set.

        * GLX_TEXTURE_TARGET_EXT is set to GLX_TEXTURE_RECTANGLE_EXT
          and <config> does not have GLX_TEXTURE_RECTANGLE_BIT_EXT set.

    A BadValue error is generated if GLX_TEXTURE_FORMAT_EXT is not
    GLX_TEXTURE_FORMAT_NONE_EXT and the width or height of <pixmap> are
    incompatible with the specified value of GLX_TEXTURE_TARGET_EXT on this
    implementation. (e.g., the pixmap size is not a power of 2 and
    GL_ARB_texture_rectangle is not supported).

    Modify paragraph 1 of the description of glXDestroyPixmap:

    ...The storage for the GLX pixmap will be freed when it is not current
    to any client and all color buffers that are bound to a texture object
    have been released.


    Modifications to seciton 3.3.6, "Querying Attributes"

    Modify paragraph 1 of the description of glXQueryDrawable:

    ...<attribute> must be set to one of GLX_WIDTH, GLX_HEIGHT,
    GLX_PRESERVED_CONTENTS, GLX_LARGEST_PBUFFER, GLX_FBCONFIG_ID,
    GLX_TEXTURE_FORMAT_EXT, GLX_TEXTURE_TARGET_EXT or GLX_MIPMAP_TEXTURE_EXT
    or a BadValue error is generated.

    Modify paragraph 3 of the description of glXQueryDrawable:

    ...If <draw> is a GLXWindow or GLXPixmap and <attribute> is set to
    GLX_PRESERVED_CONTENTS or GLX_LARGEST_PBUFFER, or if <draw> is a
    GLXWindow or GLXPbuffer and <attribute> is set to GLX_TEXTURE_FORMAT_EXT,
    GLX_TEXTURE_TARGET_EXT, or GLX_MIPMAP_TEXTURE_EXT, the contents of <value>
    are undefined.

    Add a new section 3.3.6.1, "Texturing From Drawables"

    The command

        void glXBindTexImageEXT (Display *dpy,
                                 GLXDrawable draw,
                                 int buffer,
                                 int *attrib_list);

    defines a one- or two-dimensional texture image.  The texture image is taken
    from <buffer> and need not be copied.  The texture target, the texture
    format, and the size of the texture components are derived from attributes
    of <draw>.

    The drawable attribute GLX_TEXTURE_FORMAT_EXT determines the base internal
    format of the texture.  The component sizes are also determined by drawable
    attributes as shown in table 3.4a.

    Add new table 3.4a: Size of texture components:

    Texture component Size
    ----------------- --------------
    R                 GLX_RED_SIZE
    G                 GLX_GREEN_SIZE
    B                 GLX_BLUE_SIZE
    A                 GLX_ALPHA_SIZE

    The texture target is derived from the GLX_TEXTURE_TARGET_EXT attribute of
    <draw>.  If the texture target for the drawable is GLX_TEXTURE_2D_EXT or
    GLX_TEXTURE_RECTANGLE_EXT, then buffer defines a 2D texture for the current
    2D or rectangle texture object respectively; if the texture target is
    GLX_TEXTURE_1D_EXT, then buffer defines a 1D texture for the current 1D
    texture object.

    If <buffer> is not one of GLX_FRONT_LEFT_EXT, GLX_FRONT_RIGHT_EXT,
    GLX_BACK_LEFT_EXT, GLX_BACK_RIGHT_EXT, or GLX_AUX0_EXT through
    GLX_AUXn_EXT, where n is one less than the number of AUX buffers supported
    by the FBConfig used to create <draw>, or if the requested buffer is
    missing, a BadValue error is generated.

    <attrib_list> specifies a list of attributes for the texture.  The list has
    the same structure as described for glXChooseFBConfig.  If <attrib_list> is
    NULL or empty (first attribute of None), then all attributes assume their
    default values.  <attrib_list> must be NULL or empty.

    If <dpy> and <draw> are the display and drawable for the calling thread's
    current context, glXBindTexImageEXT performs an implicit glFlush.

    The contents of the texture after the drawable has been bound are defined
    as the result of all rendering that has completed before the call to
    glXBindTexImageEXT.  In other words, the results of any operation which
    has caused damage on the drawable prior to the glXBindTexImageEXT call
    will be represented in the texture.

    Rendering to the drawable while it is bound to a texture will leave the
    contents of the texture in an undefined state.  However, no
    synchronization between rendering and texturing is done by GLX.  It is
    the application's responsibility to implement any synchronization
    required.

    If a texture object is deleted before glXReleaseTexImageEXT is called,
    the color buffer is released.

    It is not an error to call TexImage2D, TexImage1D, CopyTexImage1D, or
    CopyTexImage2D to replace an image of a texture object that has a color
    buffer bound to it.  However, these calls will cause the color buffer to be
    released and new memory to be allocated for the texture.  Note that the
    color buffer is released even if the image that is being defined is a mipmap
    level that was not defined by the color buffer.  GenerateMipmapEXT is an
    exception.  GenerateMipmapEXT can be used to define mipmap levels for
    drawables that have been created with GLX_MIPMAP_TEXTURE_EXT set.  Calling
    GenerateMipmapEXT on a drawable that was created without
    GLX_MIPMAP_TEXTURE_EXT is undefined.

    The results of calling glXBindTexImageEXT when GENERATE_MIPMAP_SGIS is TRUE
    are undefined.

    If glXBindTexImageEXT is called and the drawable attribute
    GLX_TEXTURE_FORMAT_EXT is GLX_TEXTURE_FORMAT_NONE_EXT, then a BadMatch
    error is generated.

    Currently, only pixmaps can be bound to textures.  If <draw> is not a
    valid GLXPixmap, then a GLXBadPixmap error is generated.

    glXBindTexImageEXT is ignored if there is no current GLX rendering context.

    To release a color buffer that is being used as a texture, call

       void glXReleaseTexImageEXT (Dislpay *dpy, GLXDrawable draw, int buffer);

    <buffer> must be one of GLX_FRONT_LEFT_EXT, GLX_FRONT_RIGHT_EXT,
    GLX_BACK_LEFT_EXT, GLX_BACK_RIGHT_EXT, and GLX_AUX0_EXT through
    GLX_AUXn_EXT, where n is one less than the number of AUX buffers
    supported by the FBConfig used to create <draw> or a BadValue error
    is generated.

    The contents of the color buffer are unaffected by glXReleaseTexImageEXT.

    If the specified color buffer is no longer bound to a texture (e.g.,
    because the texture object was deleted), then glXReleaseTexImageEXT has no effect;
    no error is generated.

    When a color buffer is released (e.g., by calling glXReleaseTexImageEXT or
    implicitly by calling a routine such as TexImage2D), all textures that were
    defined by the color buffer become NULL.

    If glXReleaseTexImageEXT is called and the drawable attribute
    GLX_TEXTURE_FORMAT_EXT is GLX_TEXTURE_FORMAT_NONE_EXT, then a BadMatch
    error is generated.

    Currently, only pixmaps can be bound to textures.  If <draw> is not a
    valid GLXPixmap, then a GLXBadPixmap error is generated.


Usage Examples

    Example 1: Bind redirected window to texture:

    XGetWindowAttributes (display, window, &attrib);

    visualid = XVisualIDFromVisual (attrib.visual);

    fbconfigs = glXGetFBConfigs (display, screen, &nfbconfigs);
    for (i = 0; i < nfbconfigs; i++)
    {
        visinfo = glXGetVisualFromFBConfig (display, fbconfigs[i]);
        if (!visinfo || visinfo->visualid != visualid)
            continue;

        glXGetFBConfigAttrib (display, fbconfigs[i], GLX_DRAWABLE_TYPE, &value);
        if (!(value & GLX_PIXMAP_BIT))
            continue;

        glXGetFBConfigAttrib (display, fbconfigs[i],
                              GLX_BIND_TO_TEXTURE_TARGETS_EXT,
                              &value);
        if (!(value & GLX_TEXTURE_2D_BIT_EXT))
            continue;

        glXGetFBConfigAttrib (display, fbconfigs[i],
                              GLX_BIND_TO_TEXTURE_RGBA_EXT,
                              &value);
        if (value == FALSE)
        {
            glXGetFBConfigAttrib (display, fbconfigs[i],
                                  GLX_BIND_TO_TEXTURE_RGB_EXT,
                                  &value);
            if (value == FALSE)
                continue;
        }

        glXGetFBConfigAttrib (display, fbconfigs[i],
                              GLX_Y_INVERTED_EXT,
                              &value);
        if (value == TRUE)
        {
            top = 0.0f;
            bottom = 1.0f;
        }
        else
        {
            top = 1.0f;
            bottom = 0.0f;
        }

        break;
    }

    if (i == nfbconfigs)
        /* error 1 */

    pixmap = XCompositeNameWindowPixmap (display, window);
    pixmapAttribs = { GLX_TEXTURE_TARGET_EXT, GLX_TEXTURE_2D_EXT,
                      GLX_TEXTURE_FORMAT_EXT, GLX_TEXTURE_FORMAT_RGBA_EXT,
                      None };
    glxpixmap = glXCreatePixmap (display, fbconfigs[i], pixmap, pixmapAttribs);

    glGenTextures (1, &texture);
    glBindTexture (GL_TEXTURE_2D, texture);

    glXBindTexImageEXT (display, glxpixmap, GLX_FRONT_LEFT_EXT, NULL);

    glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    /* draw using pixmap as texture */
    glBegin (GL_QUADS);

    glTexCoord2d (0.0f, bottom);
    glVertex2d (0.0f, 0.0f);

    glTexCoord2d (0.0f, top);
    glVertex2d (0.0f, 1.0f);

    glTexCoord2d (1.0f, top);
    glVertex2d (1.0f, 1.0f);

    glTexCoord2d (1.0f, bottom);
    glVertex2d (1.0f, 0.0f);

    glEnd ();

    glXReleaseTexImageEXT (display, glxpixmap, GLX_FRONT_LEFT_EXT);


Version History
    
    1. 26 Nov 2005 - DavidR
        Initial version
    2. 01 Dec 2005 - JamesJ
        -Adapted spec language from draft version of GLX_ARB_render_texture.
        -Added glXDrawableAttribute to set attributes.
        -Modified glXBindTexImageEXT to take an attrib_list parameter.
        -Added support for cubemap and 1D texture targets.
        -Added attribute to set the texture target when creating the
         drawable.
        -Updated the issues section.
        -Added mipmap support.  Support is not required.
        -Specified results of texturing from a drawable when it has been
         rendered to while bound to a texture as undefined until
         glXReleaseTexImageEXT has been called.  Allows implementations
         that need to perform an implicit copy after rendering occurs
         to be compatible with this specification.
    3. 04 Dec 2005 - DavidR
        -Changed name to GLX_EXT_texture_from_pixmap.
        -Changed spec regarding what happens when a pixmap that is bound
         to a texture is rendered to. Having textures be undefined once
         they are rendered to makes it useless for a compositing manager,
         which is a major use case for this extension.
        -Added support for not specifying texture target when creating a
         pixmap. Allows implementations to select whatever target it
         finds most suitable.
    4. 05 Dec 2005 - JamesJ
        -Changed the default value of GLX_TEXTURE_TARGET_EXT from
         GLX_NO_TEXTURE_EXT to something usable.  Eliminated
         GLX_NO_TEXTURE_EXT.
        -Eliminated GLX_TEXTURE_NONE_EXT.
        -Removed language referring to sharing of color buffers when
         pixmaps are bound to textures.
        -Updated issues.

    5. 13 Dec 2005 - JamesJ
        -Removed cube map support and rendering to multiple mipmap
         levels support.

    6. 20 Jan 2006 - JamesJ
        -Specified textures are y-inverted.

    7. 23 Jan 2006 - AaronP
        -Fix typos, make some things clearer.  Replace ocurrences of "released
         back to the drawable" with "released".

    8. 01 Feb 2006 - AndyR
        -Fix minor typos.

    9. 03 Feb 2006 - JamesJ
        -Added some new issues and their resolutions.
        -Finalized some issues that had been in discussion.
        -Made drawable y-inversion a queryable attribute of the drawable.
        -Moved detailed explanation of y-inverted addressing to the issues
         section
        -Updated example to demonstrate proper use of the y-inverted
         attribute.

    10. 06 Feb 2006 - DavidR
        -Made GLX_Y_INVERTED_EXT an FBConfig attribute instead of a drawable
         attribute.
        -Removed GLX_TEXTURE_CUBE_MAP_EXT.
        -Fix minor typo.

    11. 07 Feb 2006 - JamesJ
        -Added description of GLX_Y_INVERTED_EXT GLXFBConfig attribute, based
         on description of the drawable attribute of the same name from
         and earlier version of the specification.
        -Removed language requiring applications to re-bind a pixmap to a
         texture to gurantee contents of the texture are updated after a
         pixmap has been rendered to.
        -Added Aaron Plattner and Andy Ritger to contributors section.

    12. 14 Feb 2006 - JamesJ
        -Disallowed rendering to a drawable while it is bound as a texture
         and defined the exact contents of a texture after a drawable has
         been bound to it.

    13. 09 Mar 2006 - JamesJ
        -Add a context tag member to the vendor private requests.  This field
         is part of the vendor private header, and is needed to specify which
         context the BindTexImageEXT and ReleaseTexImageEXT requests correspond
         to.
        -Changed texture target bitfield values to not skip numbers removed in
         earlier updates.

    14. 13 Mar 2006 - JamesJ
        -Only require GLX_SGIX_fbconfig + GLX 1.2.
        -Clarify language regarding the result of rendering to drawables bound
         to textures.
        -Added GLX_FRONT_EXT and GLX_BACK_EXT tokens.

    15. 18 Apr 2006 - JamesJ
        -Allocated enum values and opcodes.
        -Require GLX 1.3.  GLX_SGIX_fbconfig doesn't allow creating pixmaps
         with attributes.
        -Added more arguments for not supporting rendering to multiple levels
         of a texture with this extension.
        -Fixed the inconsistencies in the return type of glXBindTexImageEXT
         and glXReleaseTexImageEXT.  It is now listed as void throughout.

    16. 12 Sep 2006 - JamesJ
        -Fix ordering of GLX protocol

    17. 10 Feb 2009 - Jon Leech
	-Fix typo reported by Jonathan Knispel.