mesa/main/stencil.c

/* $Id: stencil.c,v 1.9 1999/11/11 01:22:27 brianp Exp $ */

/*
 * Mesa 3-D graphics library
 * Version:  3.3
 *
 * Copyright (C) 1999  Brian Paul   All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */


#ifdef PC_HEADER
#include "all.h"
#else
#include "glheader.h"
#include "context.h"
#include "mem.h"
#include "pb.h"
#include "stencil.h"
#include "types.h"
#include "enable.h"
#endif


#if STENCIL_BITS==8
#  define STENCIL_MAX 0xff
#elif STENCIL_BITS==16
#  define STENCIL_MAX 0xffff
#else
   illegal number of stencil bits
#endif


/*
 * Return the address of a stencil buffer value given the window coords:
 */
#define STENCIL_ADDRESS(X,Y)  (ctx->Buffer->Stencil + ctx->Buffer->Width * (Y) + (X))


void
_mesa_ClearStencil( GLint s )
{
   GET_CURRENT_CONTEXT(ctx);
   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx, "glClearStencil");
   ctx->Stencil.Clear = (GLstencil) s;

   if (ctx->Driver.ClearStencil) {
      (*ctx->Driver.ClearStencil)( ctx, s );
   }
}


void
_mesa_StencilFunc( GLenum func, GLint ref, GLuint mask )
{
   GET_CURRENT_CONTEXT(ctx);
   GLint maxref;

   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx, "glStencilFunc");

   switch (func) {
      case GL_NEVER:
      case GL_LESS:
      case GL_LEQUAL:
      case GL_GREATER:
      case GL_GEQUAL:
      case GL_EQUAL:
      case GL_NOTEQUAL:
      case GL_ALWAYS:
         ctx->Stencil.Function = func;
         break;
      default:
         gl_error( ctx, GL_INVALID_ENUM, "glStencilFunc" );
         return;
   }

   maxref = (1 << STENCIL_BITS) - 1;
   ctx->Stencil.Ref = (GLstencil) CLAMP( ref, 0, maxref );
   ctx->Stencil.ValueMask = (GLstencil) mask;

   if (ctx->Driver.StencilFunc) {
      (*ctx->Driver.StencilFunc)( ctx, func, ctx->Stencil.Ref, mask );
   }
}


void
_mesa_StencilMask( GLuint mask )
{
   GET_CURRENT_CONTEXT(ctx);
   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx, "glStencilMask");
   ctx->Stencil.WriteMask = (GLstencil) mask;

   if (ctx->Driver.StencilMask) {
      (*ctx->Driver.StencilMask)( ctx, mask );
   }
}


void
_mesa_StencilOp( GLenum fail, GLenum zfail, GLenum zpass )
{
   GET_CURRENT_CONTEXT(ctx);
   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx, "glStencilOp");
   switch (fail) {
      case GL_KEEP:
      case GL_ZERO:
      case GL_REPLACE:
      case GL_INCR:
      case GL_DECR:
      case GL_INVERT:
      case GL_INCR_WRAP_EXT:
      case GL_DECR_WRAP_EXT:
         ctx->Stencil.FailFunc = fail;
         break;
      default:
         gl_error( ctx, GL_INVALID_ENUM, "glStencilOp" );
         return;
   }
   switch (zfail) {
      case GL_KEEP:
      case GL_ZERO:
      case GL_REPLACE:
      case GL_INCR:
      case GL_DECR:
      case GL_INVERT:
      case GL_INCR_WRAP_EXT:
      case GL_DECR_WRAP_EXT:
         ctx->Stencil.ZFailFunc = zfail;
         break;
      default:
         gl_error( ctx, GL_INVALID_ENUM, "glStencilOp" );
         return;
   }
   switch (zpass) {
      case GL_KEEP:
      case GL_ZERO:
      case GL_REPLACE:
      case GL_INCR:
      case GL_DECR:
      case GL_INVERT:
      case GL_INCR_WRAP_EXT:
      case GL_DECR_WRAP_EXT:
         ctx->Stencil.ZPassFunc = zpass;
         break;
      default:
         gl_error( ctx, GL_INVALID_ENUM, "glStencilOp" );
         return;
   }

   if (ctx->Driver.StencilOp) {
      (*ctx->Driver.StencilOp)( ctx, fail, zfail, zpass );
   }
}


/* Stencil Logic:

IF stencil test fails THEN
   Don't write the pixel (RGBA,Z)
   Execute FailOp
ELSE
   Write the pixel
ENDIF

Perform Depth Test

IF depth test passes OR no depth buffer THEN
   Execute ZPass
   Write the pixel
ELSE
   Execute ZFail
ENDIF

*/


/*
 * Apply the given stencil operator for each pixel in the span whose
 * mask flag is set.
 * Input:  n - number of pixels in the span
 *         x, y - location of leftmost pixel in the span
 *         oper - the stencil buffer operator
 *         mask - array [n] of flag:  1=apply operator, 0=don't apply operator
 */
static void apply_stencil_op_to_span( GLcontext *ctx,
                                      GLuint n, GLint x, GLint y,
				      GLenum oper, GLubyte mask[] )
{
   const GLstencil ref = ctx->Stencil.Ref;
   const GLstencil wrtmask = ctx->Stencil.WriteMask;
   const GLstencil invmask = (GLstencil) (~ctx->Stencil.WriteMask);
   GLstencil *stencil = STENCIL_ADDRESS( x, y );
   GLuint i;

   switch (oper) {
      case GL_KEEP:
         /* do nothing */
         break;
      case GL_ZERO:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
		  stencil[i] = 0;
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
		  stencil[i] = (GLstencil) (stencil[i] & invmask);
	       }
	    }
	 }
	 break;
      case GL_REPLACE:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  stencil[i] = ref;
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
		  GLstencil s = stencil[i];
		  stencil[i] = (GLstencil) ((invmask & s ) | (wrtmask & ref));
	       }
	    }
	 }
	 break;
      case GL_INCR:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
		  GLstencil s = stencil[i];
		  if (s < STENCIL_MAX) {
		     stencil[i] = (GLstencil) (s+1);
		  }
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
		  /* VERIFY logic of adding 1 to a write-masked value */
		  GLstencil s = stencil[i];
		  if (s < STENCIL_MAX) {
		     stencil[i] = (GLstencil) ((invmask & s) | (wrtmask & (s+1)));
		  }
	       }
	    }
	 }
	 break;
      case GL_DECR:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
		  GLstencil s = stencil[i];
		  if (s>0) {
		     stencil[i] = (GLstencil) (s-1);
		  }
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
		  /* VERIFY logic of subtracting 1 to a write-masked value */
		  GLstencil s = stencil[i];
		  if (s>0) {
		     stencil[i] = (GLstencil) ((invmask & s) | (wrtmask & (s-1)));
		  }
	       }
	    }
	 }
	 break;
      case GL_INCR_WRAP_EXT:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  stencil[i]++;
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil s = stencil[i];
                  stencil[i] = (GLstencil) ((invmask & s) | (wrtmask & (stencil[i]+1)));
	       }
	    }
	 }
	 break;
      case GL_DECR_WRAP_EXT:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
		  stencil[i]--;
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil s = stencil[i];
                  stencil[i] = (GLstencil) ((invmask & s) | (wrtmask & (stencil[i]-1)));
	       }
	    }
	 }
	 break;
      case GL_INVERT:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
		  GLstencil s = stencil[i];
		  stencil[i] = (GLstencil) ~s;
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
		  GLstencil s = stencil[i];
		  stencil[i] = (GLstencil) ((invmask & s) | (wrtmask & ~s));
	       }
	    }
	 }
	 break;
      default:
         gl_problem(ctx, "Bad stencilop in apply_stencil_op_to_span");
   }
}


/*
 * Apply stencil test to a span of pixels before depth buffering.
 * Input:  n - number of pixels in the span
 *         x, y - coordinate of left-most pixel in the span
 *         mask - array [n] of flag:  0=skip the pixel, 1=stencil the pixel
 * Output:  mask - pixels which fail the stencil test will have their
 *                 mask flag set to 0.
 * Return:  0 = all pixels failed, 1 = zero or more pixels passed.
 */
GLint gl_stencil_span( GLcontext *ctx,
                       GLuint n, GLint x, GLint y, GLubyte mask[] )
{
   GLubyte fail[MAX_WIDTH];
   GLint allfail = 0;
   GLuint i;
   GLstencil r, s;
   GLstencil *stencil;

   stencil = STENCIL_ADDRESS( x, y );

   /*
    * Perform stencil test.  The results of this operation are stored
    * in the fail[] array:
    *   IF fail[i] is non-zero THEN
    *       the stencil fail operator is to be applied
    *   ELSE
    *       the stencil fail operator is not to be applied
    *   ENDIF
    */
   switch (ctx->Stencil.Function) {
      case GL_NEVER:
         /* always fail */
         for (i=0;i<n;i++) {
	    if (mask[i]) {
	       mask[i] = 0;
	       fail[i] = 1;
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 allfail = 1;
	 break;
      case GL_LESS:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
	       s = (GLstencil) (stencil[i] & ctx->Stencil.ValueMask);
	       if (r < s) {
		  /* passed */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_LEQUAL:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
	       s = (GLstencil) (stencil[i] & ctx->Stencil.ValueMask);
	       if (r <= s) {
		  /* pass */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_GREATER:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
	       s = (GLstencil) (stencil[i] & ctx->Stencil.ValueMask);
	       if (r > s) {
		  /* passed */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_GEQUAL:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
	       s = (GLstencil) (stencil[i] & ctx->Stencil.ValueMask);
	       if (r >= s) {
		  /* passed */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_EQUAL:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
	       s = (GLstencil) (stencil[i] & ctx->Stencil.ValueMask);
	       if (r == s) {
		  /* passed */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_NOTEQUAL:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
	       s = (GLstencil) (stencil[i] & ctx->Stencil.ValueMask);
	       if (r != s) {
		  /* passed */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_ALWAYS:
	 /* always pass */
	 for (i=0;i<n;i++) {
	    fail[i] = 0;
	 }
	 break;
      default:
         gl_problem(ctx, "Bad stencil func in gl_stencil_span");
         return 0;
   }

   apply_stencil_op_to_span( ctx, n, x, y, ctx->Stencil.FailFunc, fail );

   return (allfail) ? 0 : 1;
}


/*
 * Apply the combination depth-buffer/stencil operator to a span of pixels.
 * Input:  n - number of pixels in the span
 *         x, y - location of leftmost pixel in span
 *         z - array [n] of z values
 * Input:  mask - array [n] of flags  (1=test this pixel, 0=skip the pixel)
 * Output:  mask - array [n] of flags (1=depth test passed, 0=failed)
 */
void gl_depth_stencil_span( GLcontext *ctx,
                            GLuint n, GLint x, GLint y, const GLdepth z[],
			    GLubyte mask[] )
{
   if (ctx->Depth.Test==GL_FALSE) {
      /*
       * No depth buffer, just apply zpass stencil function to active pixels.
       */
      apply_stencil_op_to_span( ctx, n, x, y, ctx->Stencil.ZPassFunc, mask );
   }
   else {
      /*
       * Perform depth buffering, then apply zpass or zfail stencil function.
       */
      GLubyte passmask[MAX_WIDTH], failmask[MAX_WIDTH], oldmask[MAX_WIDTH];
      GLuint i;

      /* init pass and fail masks to zero, copy mask[] to oldmask[] */
      for (i=0;i<n;i++) {
	 passmask[i] = failmask[i] = 0;
         oldmask[i] = mask[i];
      }

      /* apply the depth test */
      if (ctx->Driver.DepthTestSpan)
         (*ctx->Driver.DepthTestSpan)( ctx, n, x, y, z, mask );

      /* set the stencil pass/fail flags according to result of depth test */
      for (i=0;i<n;i++) {
         if (oldmask[i]) {
            if (mask[i]) {
               passmask[i] = 1;
            }
            else {
               failmask[i] = 1;
            }
         }
      }

      /* apply the pass and fail operations */
      apply_stencil_op_to_span( ctx, n, x, y, ctx->Stencil.ZFailFunc, failmask );
      apply_stencil_op_to_span( ctx, n, x, y, ctx->Stencil.ZPassFunc, passmask );
   }
}


/*
 * Apply the given stencil operator for each pixel in the array whose
 * mask flag is set.
 * Input:  n - number of pixels in the span
 *         x, y - array of [n] pixels
 *         operator - the stencil buffer operator
 *         mask - array [n] of flag:  1=apply operator, 0=don't apply operator
 */
static void apply_stencil_op_to_pixels( GLcontext *ctx,
                                        GLuint n, const GLint x[],
				        const GLint y[],
				        GLenum oper, GLubyte mask[] )
{
   GLuint i;
   GLstencil ref;
   GLstencil wrtmask, invmask;

   wrtmask = ctx->Stencil.WriteMask;
   invmask = (GLstencil) (~ctx->Stencil.WriteMask);

   ref = ctx->Stencil.Ref;

   switch (oper) {
      case GL_KEEP:
         /* do nothing */
         break;
      case GL_ZERO:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
                  *sptr = 0;
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
		  *sptr = (GLstencil) (invmask & *sptr);
	       }
	    }
	 }
	 break;
      case GL_REPLACE:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
                  *sptr = ref;
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
		  *sptr = (GLstencil) ((invmask & *sptr ) | (wrtmask & ref));
	       }
	    }
	 }
	 break;
      case GL_INCR:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
		  if (*sptr < STENCIL_MAX) {
		     *sptr = (GLstencil) (*sptr + 1);
		  }
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
		  if (*sptr < STENCIL_MAX) {
		     *sptr = (GLstencil) ((invmask & *sptr) | (wrtmask & (*sptr+1)));
		  }
	       }
	    }
	 }
	 break;
      case GL_DECR:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
		  if (*sptr>0) {
		     *sptr = (GLstencil) (*sptr - 1);
		  }
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
		  if (*sptr>0) {
		     *sptr = (GLstencil) ((invmask & *sptr) | (wrtmask & (*sptr-1)));
		  }
	       }
	    }
	 }
	 break;
      case GL_INCR_WRAP_EXT:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
                  *sptr = (GLstencil) (*sptr + 1);
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
                  *sptr = (GLstencil) ((invmask & *sptr) | (wrtmask & (*sptr+1)));
	       }
	    }
	 }
	 break;
      case GL_DECR_WRAP_EXT:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
                  *sptr = (GLstencil) (*sptr - 1);
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
                  *sptr = (GLstencil) ((invmask & *sptr) | (wrtmask & (*sptr-1)));
	       }
	    }
	 }
	 break;
      case GL_INVERT:
	 if (invmask==0) {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
                  *sptr = (GLstencil) (~*sptr);
	       }
	    }
	 }
	 else {
	    for (i=0;i<n;i++) {
	       if (mask[i]) {
                  GLstencil *sptr = STENCIL_ADDRESS( x[i], y[i] );
                  *sptr = (GLstencil) ((invmask & *sptr) | (wrtmask & ~*sptr));
	       }
	    }
	 }
	 break;
      default:
         gl_problem(ctx, "Bad stencilop in apply_stencil_op_to_pixels");
   }
}


/*
 * Apply stencil test to an array of pixels before depth buffering.
 * Input:  n - number of pixels in the span
 *         x, y - array of [n] pixels to stencil
 *         mask - array [n] of flag:  0=skip the pixel, 1=stencil the pixel
 * Output:  mask - pixels which fail the stencil test will have their
 *                 mask flag set to 0.
 * Return:  0 = all pixels failed, 1 = zero or more pixels passed.
 */
GLint gl_stencil_pixels( GLcontext *ctx,
                         GLuint n, const GLint x[], const GLint y[],
			 GLubyte mask[] )
{
   GLubyte fail[PB_SIZE];
   GLstencil r, s;
   GLuint i;
   GLint allfail = 0;

   /*
    * Perform stencil test.  The results of this operation are stored
    * in the fail[] array:
    *   IF fail[i] is non-zero THEN
    *       the stencil fail operator is to be applied
    *   ELSE
    *       the stencil fail operator is not to be applied
    *   ENDIF
    */

   switch (ctx->Stencil.Function) {
      case GL_NEVER:
         /* always fail */
         for (i=0;i<n;i++) {
	    if (mask[i]) {
	       mask[i] = 0;
	       fail[i] = 1;
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 allfail = 1;
	 break;
      case GL_LESS:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
               GLstencil *sptr = STENCIL_ADDRESS(x[i],y[i]);
	       s = (GLstencil) (*sptr & ctx->Stencil.ValueMask);
	       if (r < s) {
		  /* passed */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_LEQUAL:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
               GLstencil *sptr = STENCIL_ADDRESS(x[i],y[i]);
	       s = (GLstencil) (*sptr & ctx->Stencil.ValueMask);
	       if (r <= s) {
		  /* pass */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_GREATER:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
               GLstencil *sptr = STENCIL_ADDRESS(x[i],y[i]);
	       s = (GLstencil) (*sptr & ctx->Stencil.ValueMask);
	       if (r > s) {
		  /* passed */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_GEQUAL:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
               GLstencil *sptr = STENCIL_ADDRESS(x[i],y[i]);
	       s = (GLstencil) (*sptr & ctx->Stencil.ValueMask);
	       if (r >= s) {
		  /* passed */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_EQUAL:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
               GLstencil *sptr = STENCIL_ADDRESS(x[i],y[i]);
	       s = (GLstencil) (*sptr & ctx->Stencil.ValueMask);
	       if (r == s) {
		  /* passed */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_NOTEQUAL:
	 r = (GLstencil) (ctx->Stencil.Ref & ctx->Stencil.ValueMask);
	 for (i=0;i<n;i++) {
	    if (mask[i]) {
               GLstencil *sptr = STENCIL_ADDRESS(x[i],y[i]);
	       s = (GLstencil) (*sptr & ctx->Stencil.ValueMask);
	       if (r != s) {
		  /* passed */
		  fail[i] = 0;
	       }
	       else {
		  fail[i] = 1;
		  mask[i] = 0;
	       }
	    }
	    else {
	       fail[i] = 0;
	    }
	 }
	 break;
      case GL_ALWAYS:
	 /* always pass */
	 for (i=0;i<n;i++) {
	    fail[i] = 0;
	 }
	 break;
      default:
         gl_problem(ctx, "Bad stencil func in gl_stencil_pixels");
         return 0;
   }

   apply_stencil_op_to_pixels( ctx, n, x, y, ctx->Stencil.FailFunc, fail );

   return (allfail) ? 0 : 1;
}


/*
 * Apply the combination depth-buffer/stencil operator to a span of pixels.
 * Input:  n - number of pixels in the span
 *         x, y - array of [n] pixels to stencil
 *         z - array [n] of z values
 * Input:  mask - array [n] of flags  (1=test this pixel, 0=skip the pixel)
 * Output:  mask - array [n] of flags (1=depth test passed, 0=failed)
 */
void gl_depth_stencil_pixels( GLcontext *ctx,
                              GLuint n, const GLint x[], const GLint y[],
			      const GLdepth z[], GLubyte mask[] )
{
   if (ctx->Depth.Test==GL_FALSE) {
      /*
       * No depth buffer, just apply zpass stencil function to active pixels.
       */
      apply_stencil_op_to_pixels( ctx, n, x, y, ctx->Stencil.ZPassFunc, mask );
   }
   else {
      /*
       * Perform depth buffering, then apply zpass or zfail stencil function.
       */
      GLubyte passmask[PB_SIZE], failmask[PB_SIZE], oldmask[PB_SIZE];
      GLuint i;

      /* init pass and fail masks to zero */
      for (i=0;i<n;i++) {
	 passmask[i] = failmask[i] = 0;
         oldmask[i] = mask[i];
      }

      /* apply the depth test */
      if (ctx->Driver.DepthTestPixels)
         (*ctx->Driver.DepthTestPixels)( ctx, n, x, y, z, mask );

      /* set the stencil pass/fail flags according to result of depth test */
      for (i=0;i<n;i++) {
         if (oldmask[i]) {
            if (mask[i]) {
               passmask[i] = 1;
            }
            else {
               failmask[i] = 1;
            }
         }
      }

      /* apply the pass and fail operations */
      apply_stencil_op_to_pixels( ctx, n, x, y,
                                  ctx->Stencil.ZFailFunc, failmask );
      apply_stencil_op_to_pixels( ctx, n, x, y,
                                  ctx->Stencil.ZPassFunc, passmask );
   }

}


/*
 * Return a span of stencil values from the stencil buffer.
 * Input:  n - how many pixels
 *         x,y - location of first pixel
 * Output:  stencil - the array of stencil values
 */
void gl_read_stencil_span( GLcontext *ctx,
                           GLuint n, GLint x, GLint y, GLstencil stencil[] )
{
   if (ctx->Buffer->Stencil) {
      const GLstencil *s = STENCIL_ADDRESS( x, y );
#if STENCIL_BITS == 8
      MEMCPY( stencil, s, n * sizeof(GLstencil) );
#else
      GLuint i;
      for (i=0;i<n;i++)
         stencil[i] = s[i];
#endif
   }
}


/*
 * Write a span of stencil values to the stencil buffer.
 * Input:  n - how many pixels
 *         x,y - location of first pixel
 *         stencil - the array of stencil values
 */
void gl_write_stencil_span( GLcontext *ctx,
                            GLuint n, GLint x, GLint y,
			    const GLstencil stencil[] )
{
   if (ctx->Buffer->Stencil) {
      GLstencil *s = STENCIL_ADDRESS( x, y );
#if STENCIL_BITS == 8
      MEMCPY( s, stencil, n * sizeof(GLstencil) );
#else
      GLuint i;
      for (i=0;i<n;i++)
         s[i] = stencil[i];
#endif
   }
}


/*
 * Allocate a new stencil buffer.  If there's an old one it will be
 * deallocated first.  The new stencil buffer will be uninitialized.
 */
void gl_alloc_stencil_buffer( GLcontext *ctx )
{
   GLuint buffersize = ctx->Buffer->Width * ctx->Buffer->Height;

   /* deallocate current stencil buffer if present */
   if (ctx->Buffer->Stencil) {
      FREE(ctx->Buffer->Stencil);
      ctx->Buffer->Stencil = NULL;
   }

   /* allocate new stencil buffer */
   ctx->Buffer->Stencil = (GLstencil *) MALLOC(buffersize * sizeof(GLstencil));
   if (!ctx->Buffer->Stencil) {
      /* out of memory */
      _mesa_set_enable( ctx, GL_STENCIL_TEST, GL_FALSE );
      gl_error( ctx, GL_OUT_OF_MEMORY, "gl_alloc_stencil_buffer" );
   }
}


/*
 * Clear the stencil buffer.  If the stencil buffer doesn't exist yet we'll
 * allocate it now.
 */
void gl_clear_stencil_buffer( GLcontext *ctx )
{
   if (ctx->Visual->StencilBits==0 || !ctx->Buffer->Stencil) {
      /* no stencil buffer */
      return;
   }

   if (ctx->Scissor.Enabled) {
      /* clear scissor region only */
      GLint y;
      GLint width = ctx->Buffer->Xmax - ctx->Buffer->Xmin + 1;
      for (y=ctx->Buffer->Ymin; y<=ctx->Buffer->Ymax; y++) {
         GLstencil *ptr = STENCIL_ADDRESS( ctx->Buffer->Xmin, y );
#if STENCIL_BITS==8
         MEMSET( ptr, ctx->Stencil.Clear, width * sizeof(GLstencil) );
#else
         GLint x;
         for (x = 0; x < width; x++)
            ptr[x] = ctx->Stencil.Clear;
#endif
      }
   }
   else {
      /* clear whole stencil buffer */
#if STENCIL_BITS==8
      MEMSET( ctx->Buffer->Stencil, ctx->Stencil.Clear,
              ctx->Buffer->Width * ctx->Buffer->Height * sizeof(GLstencil) );
#else
      GLuint i;
      GLuint pixels = ctx->Buffer->Width * ctx->Buffer->Height;
      GLstencil *buffer = ctx->Buffer->Stencil;
      for (i = 0; i < pixels; i++)
         ptr[i] = ctx->Stencil.Clear;
#endif
   }
}