Initial revision

1 files changed, 879 insertions, 0 deletions

diff --git a/src/mesa/main/depth.c b/src/mesa/main/depth.c
new file mode 100644
index 00000000000..6d5a2be237e
--- /dev/null
+++ b/src/mesa/main/depth.c
@@ -0,0 +1,879 @@
+/* $Id: depth.c,v 1.1 1999/08/19 00:55:41 jtg Exp $ */
+
+/*
+ * Mesa 3-D graphics library
+ * Version:  3.1
+ * 
+ * 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.
+ */
+
+
+/*
+ * Depth buffer functions
+ */
+
+
+#ifdef PC_HEADER
+#include "all.h"
+#else
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include "context.h"
+#include "enums.h"
+#include "depth.h"
+#include "macros.h"
+#include "types.h"
+#ifdef XFree86Server
+#include "GL/xf86glx.h"
+#endif
+#endif
+
+
+
+/**********************************************************************/
+/*****                          API Functions                     *****/
+/**********************************************************************/
+
+
+
+void gl_ClearDepth( GLcontext* ctx, GLclampd depth )
+{
+   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx, "glClearDepth");
+   ctx->Depth.Clear = (GLfloat) CLAMP( depth, 0.0, 1.0 );
+   if (ctx->Driver.ClearDepth)
+      (*ctx->Driver.ClearDepth)( ctx, ctx->Depth.Clear );
+}
+
+
+
+void gl_DepthFunc( GLcontext* ctx, GLenum func )
+{
+   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx, "glDepthFunc");
+
+   if (MESA_VERBOSE & (VERBOSE_API|VERBOSE_TEXTURE))
+      fprintf(stderr, "glDepthFunc %s\n", gl_lookup_enum_by_nr(func));
+
+
+   switch (func) {
+      case GL_NEVER:
+      case GL_LESS:    /* (default) pass if incoming z < stored z */
+      case GL_GEQUAL:
+      case GL_LEQUAL:
+      case GL_GREATER:
+      case GL_NOTEQUAL:
+      case GL_EQUAL:
+      case GL_ALWAYS:
+	 if (ctx->Depth.Func != func) {
+	    ctx->Depth.Func = func;
+	    ctx->NewState |= NEW_RASTER_OPS;
+	    if (ctx->Driver.DepthFunc) {
+	       (*ctx->Driver.DepthFunc)( ctx, func );
+	    }
+	 }
+         break;
+      default:
+         gl_error( ctx, GL_INVALID_ENUM, "glDepth.Func" );
+   }
+}
+
+
+
+void gl_DepthMask( GLcontext* ctx, GLboolean flag )
+{
+   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx, "glDepthMask");
+
+   if (MESA_VERBOSE & (VERBOSE_API|VERBOSE_TEXTURE))
+      fprintf(stderr, "glDepthMask %d\n", flag);
+
+   /*
+    * GL_TRUE indicates depth buffer writing is enabled (default)
+    * GL_FALSE indicates depth buffer writing is disabled
+    */
+   if (ctx->Depth.Mask != flag) {
+      ctx->Depth.Mask = flag;
+      ctx->NewState |= NEW_RASTER_OPS;
+      if (ctx->Driver.DepthMask) {
+	 (*ctx->Driver.DepthMask)( ctx, flag );
+      }
+   }
+}
+
+
+
+/**********************************************************************/
+/*****                   Depth Testing Functions                  *****/
+/**********************************************************************/
+
+
+/*
+ * Depth test horizontal spans of fragments.  These functions are called
+ * via ctx->Driver.depth_test_span only.
+ *
+ * Input:  n - number of pixels in the span
+ *         x, y - location of leftmost pixel in span in window coords
+ *         z - array [n] of integer depth values
+ * In/Out:  mask - array [n] of flags (1=draw pixel, 0=don't draw) 
+ * Return:  number of pixels which passed depth test
+ */
+
+
+/*
+ * glDepthFunc( any ) and glDepthMask( GL_TRUE or GL_FALSE ).
+ */
+GLuint gl_depth_test_span_generic( GLcontext* ctx,
+                                   GLuint n, GLint x, GLint y,
+                                   const GLdepth z[],
+                                   GLubyte mask[] )
+{
+   GLdepth *zptr = Z_ADDRESS( ctx, x, y );
+   GLubyte *m = mask;
+   GLuint i;
+   GLuint passed = 0;
+
+   /* switch cases ordered from most frequent to less frequent */
+   switch (ctx->Depth.Func) {
+      case GL_LESS:
+         if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0; i<n; i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] < *zptr) {
+		     /* pass */
+		     *zptr = z[i];
+		     passed++;
+		  }
+		  else {
+		     /* fail */
+		     *m = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0; i<n; i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] < *zptr) {
+		     /* pass */
+		     passed++;
+		  }
+		  else {
+		     *m = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_LEQUAL:
+	 if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] <= *zptr) {
+		     *zptr = z[i];
+		     passed++;
+		  }
+		  else {
+		     *m = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] <= *zptr) {
+		     /* pass */
+		     passed++;
+		  }
+		  else {
+		     *m = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_GEQUAL:
+	 if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] >= *zptr) {
+		     *zptr = z[i];
+		     passed++;
+		  }
+		  else {
+		     *m = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] >= *zptr) {
+		     /* pass */
+		     passed++;
+		  }
+		  else {
+		     *m = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_GREATER:
+	 if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] > *zptr) {
+		     *zptr = z[i];
+		     passed++;
+		  }
+		  else {
+		     *m = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] > *zptr) {
+		     /* pass */
+		     passed++;
+		  }
+		  else {
+		     *m = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_NOTEQUAL:
+	 if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] != *zptr) {
+		     *zptr = z[i];
+		     passed++;
+		  }
+		  else {
+		     *m = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] != *zptr) {
+		     /* pass */
+		     passed++;
+		  }
+		  else {
+		     *m = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_EQUAL:
+	 if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] == *zptr) {
+		     *zptr = z[i];
+		     passed++;
+		  }
+		  else {
+		     *m =0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  if (z[i] == *zptr) {
+		     /* pass */
+		     passed++;
+		  }
+		  else {
+		     *m =0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_ALWAYS:
+	 if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0;i<n;i++,zptr++,m++) {
+	       if (*m) {
+		  *zptr = z[i];
+		  passed++;
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer or mask */
+	    passed = n;
+	 }
+	 break;
+      case GL_NEVER:
+	 for (i=0;i<n;i++) {
+	    mask[i] = 0;
+	 }
+	 break;
+      default:
+         gl_problem(ctx, "Bad depth func in gl_depth_test_span_generic");
+   } /*switch*/
+
+   return passed;
+}
+
+
+
+/*
+ * glDepthFunc(GL_LESS) and glDepthMask(GL_TRUE).
+ */
+GLuint gl_depth_test_span_less( GLcontext* ctx,
+                                GLuint n, GLint x, GLint y, const GLdepth z[],
+                                GLubyte mask[] )
+{
+   GLdepth *zptr = Z_ADDRESS( ctx, x, y );
+   GLuint i;
+   GLuint passed = 0;
+
+   for (i=0; i<n; i++) {
+      if (mask[i]) {
+         if (z[i] < zptr[i]) {
+            /* pass */
+            zptr[i] = z[i];
+            passed++;
+         }
+         else {
+            /* fail */
+            mask[i] = 0;
+         }
+      }
+   }
+   return passed;
+}
+
+
+/*
+ * glDepthFunc(GL_GREATER) and glDepthMask(GL_TRUE).
+ */
+GLuint gl_depth_test_span_greater( GLcontext* ctx,
+                                   GLuint n, GLint x, GLint y,
+                                   const GLdepth z[],
+                                   GLubyte mask[] )
+{
+   GLdepth *zptr = Z_ADDRESS( ctx, x, y );
+   GLuint i;
+   GLuint passed = 0;
+
+   for (i=0; i<n; i++) {
+      if (mask[i]) {
+         if (z[i] > zptr[i]) {
+            /* pass */
+            zptr[i] = z[i];
+            passed++;
+         }
+         else {
+            /* fail */
+            mask[i] = 0;
+         }
+      }
+   }
+   return passed;
+}
+
+
+
+/*
+ * Depth test an array of randomly positioned fragments.
+ */
+
+
+#define ZADDR_SETUP   GLdepth *depthbuffer = ctx->Buffer->Depth; \
+                      GLint width = ctx->Buffer->Width;
+
+#define ZADDR( X, Y )   (depthbuffer + (Y) * width + (X) )
+
+
+
+/*
+ * glDepthFunc( any ) and glDepthMask( GL_TRUE or GL_FALSE ).
+ */
+void gl_depth_test_pixels_generic( GLcontext* ctx,
+                                   GLuint n, const GLint x[], const GLint y[],
+                                   const GLdepth z[], GLubyte mask[] )
+{
+   register GLdepth *zptr;
+   register GLuint i;
+
+   /* switch cases ordered from most frequent to less frequent */
+   switch (ctx->Depth.Func) {
+      case GL_LESS:
+         if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] < *zptr) {
+		     /* pass */
+		     *zptr = z[i];
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] < *zptr) {
+		     /* pass */
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_LEQUAL:
+         if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] <= *zptr) {
+		     /* pass */
+		     *zptr = z[i];
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] <= *zptr) {
+		     /* pass */
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_GEQUAL:
+         if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] >= *zptr) {
+		     /* pass */
+		     *zptr = z[i];
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] >= *zptr) {
+		     /* pass */
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_GREATER:
+         if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] > *zptr) {
+		     /* pass */
+		     *zptr = z[i];
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] > *zptr) {
+		     /* pass */
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_NOTEQUAL:
+         if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] != *zptr) {
+		     /* pass */
+		     *zptr = z[i];
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] != *zptr) {
+		     /* pass */
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_EQUAL:
+         if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] == *zptr) {
+		     /* pass */
+		     *zptr = z[i];
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  if (z[i] == *zptr) {
+		     /* pass */
+		  }
+		  else {
+		     /* fail */
+		     mask[i] = 0;
+		  }
+	       }
+	    }
+	 }
+	 break;
+      case GL_ALWAYS:
+	 if (ctx->Depth.Mask) {
+	    /* Update Z buffer */
+	    for (i=0; i<n; i++) {
+	       if (mask[i]) {
+		  zptr = Z_ADDRESS(ctx,x[i],y[i]);
+		  *zptr = z[i];
+	       }
+	    }
+	 }
+	 else {
+	    /* Don't update Z buffer or mask */
+	 }
+	 break;
+      case GL_NEVER:
+	 /* depth test never passes */
+	 for (i=0;i<n;i++) {
+	    mask[i] = 0;
+	 }
+	 break;
+      default:
+         gl_problem(ctx, "Bad depth func in gl_depth_test_pixels_generic");
+   } /*switch*/
+}
+
+
+
+/*
+ * glDepthFunc( GL_LESS ) and glDepthMask( GL_TRUE ).
+ */
+void gl_depth_test_pixels_less( GLcontext* ctx,
+                                GLuint n, const GLint x[], const GLint y[],
+                                const GLdepth z[], GLubyte mask[] )
+{
+   GLdepth *zptr;
+   GLuint i;
+
+   for (i=0; i<n; i++) {
+      if (mask[i]) {
+         zptr = Z_ADDRESS(ctx,x[i],y[i]);
+         if (z[i] < *zptr) {
+            /* pass */
+            *zptr = z[i];
+         }
+         else {
+            /* fail */
+            mask[i] = 0;
+         }
+      }
+   }
+}
+
+
+/*
+ * glDepthFunc( GL_GREATER ) and glDepthMask( GL_TRUE ).
+ */
+void gl_depth_test_pixels_greater( GLcontext* ctx,
+                                   GLuint n, const GLint x[], const GLint y[],
+                                   const GLdepth z[], GLubyte mask[] )
+{
+   GLdepth *zptr;
+   GLuint i;
+
+   for (i=0; i<n; i++) {
+      if (mask[i]) {
+         zptr = Z_ADDRESS(ctx,x[i],y[i]);
+         if (z[i] > *zptr) {
+            /* pass */
+            *zptr = z[i];
+         }
+         else {
+            /* fail */
+            mask[i] = 0;
+         }
+      }
+   }
+}
+
+
+
+
+/**********************************************************************/
+/*****                      Read Depth Buffer                     *****/
+/**********************************************************************/
+
+
+/*
+ * Return a span of depth values from the depth buffer as floats in [0,1].
+ * This function is only called through Driver.read_depth_span_float()
+ * Input:  n - how many pixels
+ *         x,y - location of first pixel
+ * Output:  depth - the array of depth values
+ */
+void gl_read_depth_span_float( GLcontext* ctx,
+                               GLuint n, GLint x, GLint y, GLfloat depth[] )
+{
+   GLdepth *zptr;
+   GLfloat scale;
+   GLuint i;
+
+   scale = 1.0F / DEPTH_SCALE;
+
+   if (ctx->Buffer->Depth) {
+      zptr = Z_ADDRESS( ctx, x, y );
+      for (i=0;i<n;i++) {
+	 depth[i] = (GLfloat) zptr[i] * scale;
+      }
+   }
+   else {
+      for (i=0;i<n;i++) {
+	 depth[i] = 0.0F;
+      }
+   }
+}
+
+
+/*
+ * Return a span of depth values from the depth buffer as integers in
+ * [0,MAX_DEPTH].
+ * This function is only called through Driver.read_depth_span_int()
+ * Input:  n - how many pixels
+ *         x,y - location of first pixel
+ * Output:  depth - the array of depth values
+ */
+void gl_read_depth_span_int( GLcontext* ctx,
+                             GLuint n, GLint x, GLint y, GLdepth depth[] )
+{
+   if (ctx->Buffer->Depth) {
+      GLdepth *zptr = Z_ADDRESS( ctx, x, y );
+      MEMCPY( depth, zptr, n * sizeof(GLdepth) );
+   }
+   else {
+      GLuint i;
+      for (i=0;i<n;i++) {
+	 depth[i] = 0;
+      }
+   }
+}
+
+
+
+/**********************************************************************/
+/*****                Allocate and Clear Depth Buffer             *****/
+/**********************************************************************/
+
+
+
+/*
+ * Allocate a new depth buffer.  If there's already a depth buffer allocated
+ * it will be free()'d.  The new depth buffer will be uniniitalized.
+ * This function is only called through Driver.alloc_depth_buffer.
+ */
+void gl_alloc_depth_buffer( GLcontext* ctx )
+{
+   /* deallocate current depth buffer if present */
+   if (ctx->Buffer->Depth) {
+      free(ctx->Buffer->Depth);
+      ctx->Buffer->Depth = NULL;
+   }
+
+   /* allocate new depth buffer, but don't initialize it */
+   ctx->Buffer->Depth = (GLdepth *) malloc( ctx->Buffer->Width
+                                            * ctx->Buffer->Height
+                                            * sizeof(GLdepth) );
+   if (!ctx->Buffer->Depth) {
+      /* out of memory */
+      ctx->Depth.Test = GL_FALSE;
+      gl_error( ctx, GL_OUT_OF_MEMORY, "Couldn't allocate depth buffer" );
+   }
+}
+
+
+
+
+/*
+ * Clear the depth buffer.  If the depth buffer doesn't exist yet we'll
+ * allocate it now.
+ * This function is only called through Driver.clear_depth_buffer.
+ */
+void gl_clear_depth_buffer( GLcontext* ctx )
+{
+   GLdepth clear_value = (GLdepth) (ctx->Depth.Clear * DEPTH_SCALE);
+   
+   if (ctx->Visual->DepthBits==0 || !ctx->Buffer->Depth || !ctx->Depth.Mask) {
+      /* no depth buffer, or writing to it is disabled */
+      return;
+   }
+
+   /* The loops in this function have been written so the IRIX 5.3
+    * C compiler can unroll them.  Hopefully other compilers can too!
+    */
+
+   if (ctx->Scissor.Enabled) {
+      /* only clear scissor region */
+      GLint y;
+      for (y=ctx->Buffer->Ymin; y<=ctx->Buffer->Ymax; y++) {
+         GLdepth *d = Z_ADDRESS( ctx, ctx->Buffer->Xmin, y );
+         GLint n = ctx->Buffer->Xmax - ctx->Buffer->Xmin + 1;
+         do {
+            *d++ = clear_value;
+            n--;
+         } while (n);
+      }
+   }
+   else {
+      /* clear whole buffer */
+      if (sizeof(GLdepth)==2 && (clear_value&0xff)==(clear_value>>8)) {
+         /* lower and upper bytes of clear_value are same, use MEMSET */
+         MEMSET( ctx->Buffer->Depth, clear_value&0xff,
+                 2*ctx->Buffer->Width*ctx->Buffer->Height);
+      }
+      else {
+         GLdepth *d = ctx->Buffer->Depth;
+         GLint n = ctx->Buffer->Width * ctx->Buffer->Height;
+         while (n>=16) {
+            d[0] = clear_value;    d[1] = clear_value;
+            d[2] = clear_value;    d[3] = clear_value;
+            d[4] = clear_value;    d[5] = clear_value;
+            d[6] = clear_value;    d[7] = clear_value;
+            d[8] = clear_value;    d[9] = clear_value;
+            d[10] = clear_value;   d[11] = clear_value;
+            d[12] = clear_value;   d[13] = clear_value;
+            d[14] = clear_value;   d[15] = clear_value;
+            d += 16;
+            n -= 16;
+         }
+         while (n>0) {
+            *d++ = clear_value;
+            n--;
+         }
+      }
+   }
+}
+
+
+