/* Copyright (c) Dietmar Planitzer, 1998, 2002 */

/* This program is freely distributable without licensing fees 

   and is provided without guarantee or warrantee expressed or 

   implied. This program is -not- in the public domain. */

#import "macx_glut.h"

#import "GLUTView.h"

/* CENTRY */

void APIENTRY glutEstablishOverlay(void)

{

    /* not implemented */

   /* If you want to know why we don't support overlays,

      then read this: */

  /* XXX For now, transparent RGBA overlays are not supported

     by GLUT.  RGBA overlays raise difficult questions about

     what the transparent pixel (really color) value should be.

     Color index overlay transparency is "easy" because the

     transparent pixel value does not affect displayable colors

     (except for stealing one color cell) since colors are

     determined by indirection through a colormap, and because

     it is uncommon for arbitrary pixel values in color index to

     be "calculated" (as can occur with a host of RGBA operations

     like lighting, blending, etc) so it is easy to avoid the

     transparent pixel value.

     Since it is typically easy to avoid the transparent pixel

     value in color index mode, if GLUT tells the programmer what

     pixel is transparent, then most program can easily avoid

     generating that pixel value except when they intend

     transparency.  GLUT returns whatever transparent pixel value

     is provided by the system through glutGet(

     GLUT_TRANSPARENT_INDEX).

     Theory versus practice for RGBA overlay transparency: In

     theory, the reasonable thing is enabling overlay transparency

     when an overlay pixel's destination alpha is 0 because this

     allows overlay transparency to be controlled via alpha and all

     visibile colors are permited, but no hardware I am aware of

     supports this practice (and it requires destination alpha which

     is typically optional and quite uncommon for overlay windows!). 

     In practice, the choice of  transparent pixel value is typically

     "hardwired" into most graphics hardware to a single pixel value.

     SGI hardware uses true black (0,0,0) without regard for the

     destination alpha.  This is far from ideal because true black (a

     common color that is easy to accidently generate) can not be

     generated in an RGBA overlay. I am not sure what other vendors

     do.

     Pragmatically, most of the typical things you want to do in the

     overlays can be done in color index (rubber banding, pop-up

     menus, etc.).  One solution for GLUT would be to simply

     "advertise" what RGB triple (or possibly RGBA quadruple or simply 

     A alone) generates transparency.  The problem with this approach

     is that it forces programmers to avoid whatever arbitrary color

     various systems decide is transparent.  This is a difficult

     burden to place on programmers that want to portably make use of

     overlays.

     To actually support transparent RGBA overlays, there are really

     two reaonsable options.  ONE: Simply mandate that true black is

     the RGBA overlay transparent color (what IRIS GL did).  This is

     nice for programmers since only one option, nice for existing SGI 

     hardware, bad for anyone (including SGI) who wants to improve

     upon "true black" RGB transparency. 

     Or TWO: Provide a set of queriable "transparency types" (like

     "true black" or "alpha == 0" or "true white" or even a queriable

     transparent color).  This is harder for programmers, OK for

     existing SGI hardware, and it leaves open the issue of what other 

     modes are reasonable.

     Option TWO seems the more general approach, but since hardware

     designers will likely only implement a single mode (this is a

     scan out issue where bandwidth is pressing issue), codifying

     multiple speculative approaches nobody may ever implement seems

     silly.  And option ONE fiats a suboptimal solution.

     Therefore, I defer any decision of how GLUT should support RGBA

     overlay transparency and leave support for it unimplemented.

     Nobody has been pressing me for RGBA overlay transparency (though 

     people have requested color index overlay transparency

     repeatedly).  Geez, if you read this far you are either really

     bored or maybe actually  interested in this topic.  Anyway, if

     you have ideas (particularly if you plan on implementing a

     hardware scheme for RGBA overlay transparency), I'd be

     interested.

     For the record, SGI's expiremental Framebufer Configuration

     experimental GLX extension uses option TWO.  Transparency modes

     for "none" and "RGB" are defined (others could be defined later). 

     What RGB value is the transparent one must be queried. 

     I was hoping GLUT could have something that required less work

     from the programmer to use portably. -mjk */

  __glutWarning("Overlays are not supported by Mac OS X GLUT (for now).");

}

void APIENTRY glutUseLayer(GLenum layer)

{

    if(layer != GLUT_NORMAL || layer != GLUT_OVERLAY)

        __glutWarning("glutUseLayer: unknown layer, %d.", layer);

    /* not implemented */

}

void APIENTRY glutRemoveOverlay(void)

{

    /* not implemented */

}

void APIENTRY glutPostOverlayRedisplay(void)

{

    /* not implemented */

}

void APIENTRY glutPostWindowOverlayRedisplay(int win)

{

    /* not implemented */

}

void APIENTRY glutShowOverlay(void)

{

    /* not implemented */

}

void APIENTRY glutHideOverlay(void)

{

    /* not implemented */

}

void APIENTRY glutOverlayDisplayFunc(void (*func)(void))

{

    /* not implemented */

}

int APIENTRY glutLayerGet(GLenum param)

{

    switch(param) {

        case GLUT_OVERLAY_POSSIBLE:

            return 0;

        case GLUT_LAYER_IN_USE:

            return GLUT_NORMAL;

        case GLUT_HAS_OVERLAY:

            return 0;

        case GLUT_TRANSPARENT_INDEX:

            return -1;

        case GLUT_NORMAL_DAMAGED:

            return [__glutCurrentView isDamaged];

        case GLUT_OVERLAY_DAMAGED:

            return -1;

        default:

            __glutWarning("invalid glutLayerGet parameter: %d", param);

            return -1;      

    }

}

/* ENDCENTRY */