path: root/src/gallium/drivers/softpipe/sp_quad_depth_test.c

/**************************************************************************
 * 
 * Copyright 2007 Tungsten Graphics, Inc., Cedar Park, Texas.
 * 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, sub license, 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 (including the
 * next paragraph) 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 NON-INFRINGEMENT.
 * IN NO EVENT SHALL TUNGSTEN GRAPHICS AND/OR ITS SUPPLIERS 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.
 * 
 **************************************************************************/

/**
 * \brief  Quad depth testing
 */

#include "pipe/p_defines.h"
#include "util/u_memory.h"
#include "tgsi/tgsi_scan.h"
#include "sp_context.h"
#include "sp_quad.h"
#include "sp_surface.h"
#include "sp_quad_pipe.h"
#include "sp_tile_cache.h"
#include "sp_state.h"           /* for sp_fragment_shader */


struct depth_data {
   struct pipe_surface *ps;
   enum pipe_format format;
   unsigned bzzzz[QUAD_SIZE];  /**< Z values fetched from depth buffer */
   unsigned qzzzz[QUAD_SIZE];  /**< Z values from the quad */
   ubyte stencilVals[QUAD_SIZE];
   struct softpipe_cached_tile *tile;
};



static void
get_depth_stencil_values( struct depth_data *data,
                          const struct quad_header *quad )
{
   unsigned j;
   const struct softpipe_cached_tile *tile = data->tile;

   switch (data->format) {
   case PIPE_FORMAT_Z16_UNORM:
      for (j = 0; j < QUAD_SIZE; j++) {
         int x = quad->input.x0 % TILE_SIZE + (j & 1);
         int y = quad->input.y0 % TILE_SIZE + (j >> 1);
         data->bzzzz[j] = tile->data.depth16[y][x];
      }
      break;
   case PIPE_FORMAT_Z32_UNORM:
      for (j = 0; j < QUAD_SIZE; j++) {
         int x = quad->input.x0 % TILE_SIZE + (j & 1);
         int y = quad->input.y0 % TILE_SIZE + (j >> 1);
         data->bzzzz[j] = tile->data.depth32[y][x];
      }
      break;
   case PIPE_FORMAT_X8Z24_UNORM:
   case PIPE_FORMAT_S8Z24_UNORM:
      for (j = 0; j < QUAD_SIZE; j++) {
         int x = quad->input.x0 % TILE_SIZE + (j & 1);
         int y = quad->input.y0 % TILE_SIZE + (j >> 1);
         data->bzzzz[j] = tile->data.depth32[y][x] & 0xffffff;
         data->stencilVals[j] = tile->data.depth32[y][x] >> 24;
      }
   break;
   case PIPE_FORMAT_Z24X8_UNORM:
   case PIPE_FORMAT_Z24S8_UNORM:
      for (j = 0; j < QUAD_SIZE; j++) {
         int x = quad->input.x0 % TILE_SIZE + (j & 1);
         int y = quad->input.y0 % TILE_SIZE + (j >> 1);
         data->bzzzz[j] = tile->data.depth32[y][x] >> 8;
         data->stencilVals[j] = tile->data.depth32[y][x] & 0xff;
      }
      break;
   default:
      assert(0);
   }
}

/* If the shader has not been run, interpolate the depth values
 * ourselves.
 */
static void
interpolate_quad_depth( struct quad_header *quad )
{
   const float fx = (float) quad->input.x0;
   const float fy = (float) quad->input.y0;
   const float dzdx = quad->posCoef->dadx[2];
   const float dzdy = quad->posCoef->dady[2];
   const float z0 = quad->posCoef->a0[2] + dzdx * fx + dzdy * fy;

   quad->output.depth[0] = z0;
   quad->output.depth[1] = z0 + dzdx;
   quad->output.depth[2] = z0 + dzdy;
   quad->output.depth[3] = z0 + dzdx + dzdy;
}


static void
convert_quad_depth( struct depth_data *data, 
                    const struct quad_header *quad )
{
   unsigned j;

   /* Convert quad's float depth values to int depth values (qzzzz).
    * If the Z buffer stores integer values, we _have_ to do the depth
    * compares with integers (not floats).  Otherwise, the float->int->float
    * conversion of Z values (which isn't an identity function) will cause
    * Z-fighting errors.
    */
   switch (data->format) {
   case PIPE_FORMAT_Z16_UNORM:
      {
         float scale = 65535.0;

         for (j = 0; j < QUAD_SIZE; j++) {
            data->qzzzz[j] = (unsigned) (quad->output.depth[j] * scale);
         }
      }
      break;
   case PIPE_FORMAT_Z32_UNORM:
      {
         double scale = (double) (uint) ~0UL;

         for (j = 0; j < QUAD_SIZE; j++) {
            data->qzzzz[j] = (unsigned) (quad->output.depth[j] * scale);
         }
      }
      break;
   case PIPE_FORMAT_X8Z24_UNORM:
   case PIPE_FORMAT_S8Z24_UNORM:
      {
         float scale = (float) ((1 << 24) - 1);

         for (j = 0; j < QUAD_SIZE; j++) {
            data->qzzzz[j] = (unsigned) (quad->output.depth[j] * scale);
         }
      }
      break;
   case PIPE_FORMAT_Z24X8_UNORM:
   case PIPE_FORMAT_Z24S8_UNORM:
      {
         float scale = (float) ((1 << 24) - 1);

         for (j = 0; j < QUAD_SIZE; j++) {
            data->qzzzz[j] = (unsigned) (quad->output.depth[j] * scale);
         }
      }
      break;
   default:
      assert(0);
   }
}



static void
write_depth_stencil_values( struct depth_data *data,
                            struct quad_header *quad )
{
   struct softpipe_cached_tile *tile = data->tile;
   unsigned j;

   /* put updated Z values back into cached tile */
   switch (data->format) {
   case PIPE_FORMAT_Z16_UNORM:
      for (j = 0; j < QUAD_SIZE; j++) {
         int x = quad->input.x0 % TILE_SIZE + (j & 1);
         int y = quad->input.y0 % TILE_SIZE + (j >> 1);
         tile->data.depth16[y][x] = (ushort) data->bzzzz[j];
      }
      break;
   case PIPE_FORMAT_X8Z24_UNORM:
   case PIPE_FORMAT_Z32_UNORM:
      for (j = 0; j < QUAD_SIZE; j++) {
         int x = quad->input.x0 % TILE_SIZE + (j & 1);
         int y = quad->input.y0 % TILE_SIZE + (j >> 1);
         tile->data.depth32[y][x] = data->bzzzz[j];
      }
      break;
   case PIPE_FORMAT_S8Z24_UNORM:
      for (j = 0; j < QUAD_SIZE; j++) {
         int x = quad->input.x0 % TILE_SIZE + (j & 1);
         int y = quad->input.y0 % TILE_SIZE + (j >> 1);
         tile->data.depth32[y][x] = (data->stencilVals[j] << 24) | data->bzzzz[j];
      }
      break;
   case PIPE_FORMAT_Z24S8_UNORM:
      for (j = 0; j < QUAD_SIZE; j++) {
         int x = quad->input.x0 % TILE_SIZE + (j & 1);
         int y = quad->input.y0 % TILE_SIZE + (j >> 1);
         tile->data.depth32[y][x] = (data->bzzzz[j] << 8) | data->stencilVals[j];
      }
      break;
   case PIPE_FORMAT_Z24X8_UNORM:
      for (j = 0; j < QUAD_SIZE; j++) {
         int x = quad->input.x0 % TILE_SIZE + (j & 1);
         int y = quad->input.y0 % TILE_SIZE + (j >> 1);
         tile->data.depth32[y][x] = data->bzzzz[j] << 8;
      }
      break;
   default:
      assert(0);
   }
}




/** Only 8-bit stencil supported */
#define STENCIL_MAX 0xff


/**
 * Do the basic stencil test (compare stencil buffer values against the
 * reference value.
 *
 * \param data->stencilVals  the stencil values from the stencil buffer
 * \param func  the stencil func (PIPE_FUNC_x)
 * \param ref  the stencil reference value
 * \param valMask  the stencil value mask indicating which bits of the stencil
 *                 values and ref value are to be used.
 * \return mask indicating which pixels passed the stencil test
 */
static unsigned
do_stencil_test(struct depth_data *data,
                unsigned func,
                unsigned ref, unsigned valMask)
{
   unsigned passMask = 0x0;
   unsigned j;

   ref &= valMask;

   switch (func) {
   case PIPE_FUNC_NEVER:
      /* passMask = 0x0 */
      break;
   case PIPE_FUNC_LESS:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (ref < (data->stencilVals[j] & valMask)) {
            passMask |= (1 << j);
         }
      }
      break;
   case PIPE_FUNC_EQUAL:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (ref == (data->stencilVals[j] & valMask)) {
            passMask |= (1 << j);
         }
      }
      break;
   case PIPE_FUNC_LEQUAL:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (ref <= (data->stencilVals[j] & valMask)) {
            passMask |= (1 << j);
         }
      }
      break;
   case PIPE_FUNC_GREATER:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (ref > (data->stencilVals[j] & valMask)) {
            passMask |= (1 << j);
         }
      }
      break;
   case PIPE_FUNC_NOTEQUAL:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (ref != (data->stencilVals[j] & valMask)) {
            passMask |= (1 << j);
         }
      }
      break;
   case PIPE_FUNC_GEQUAL:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (ref >= (data->stencilVals[j] & valMask)) {
            passMask |= (1 << j);
         }
      }
      break;
   case PIPE_FUNC_ALWAYS:
      passMask = MASK_ALL;
      break;
   default:
      assert(0);
   }

   return passMask;
}


/**
 * Apply the stencil operator to stencil values.
 *
 * \param data->stencilVals  the stencil buffer values (read and written)
 * \param mask  indicates which pixels to update
 * \param op  the stencil operator (PIPE_STENCIL_OP_x)
 * \param ref  the stencil reference value
 * \param wrtMask  writemask controlling which bits are changed in the
 *                 stencil values
 */
static void
apply_stencil_op(struct depth_data *data,
                 unsigned mask, unsigned op, ubyte ref, ubyte wrtMask)
{
   unsigned j;
   ubyte newstencil[QUAD_SIZE];

   for (j = 0; j < QUAD_SIZE; j++) {
      newstencil[j] = data->stencilVals[j];
   }

   switch (op) {
   case PIPE_STENCIL_OP_KEEP:
      /* no-op */
      break;
   case PIPE_STENCIL_OP_ZERO:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (mask & (1 << j)) {
            newstencil[j] = 0;
         }
      }
      break;
   case PIPE_STENCIL_OP_REPLACE:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (mask & (1 << j)) {
            newstencil[j] = ref;
         }
      }
      break;
   case PIPE_STENCIL_OP_INCR:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (mask & (1 << j)) {
            if (data->stencilVals[j] < STENCIL_MAX) {
               newstencil[j] = data->stencilVals[j] + 1;
            }
         }
      }
      break;
   case PIPE_STENCIL_OP_DECR:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (mask & (1 << j)) {
            if (data->stencilVals[j] > 0) {
               newstencil[j] = data->stencilVals[j] - 1;
            }
         }
      }
      break;
   case PIPE_STENCIL_OP_INCR_WRAP:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (mask & (1 << j)) {
            newstencil[j] = data->stencilVals[j] + 1;
         }
      }
      break;
   case PIPE_STENCIL_OP_DECR_WRAP:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (mask & (1 << j)) {
            newstencil[j] = data->stencilVals[j] - 1;
         }
      }
      break;
   case PIPE_STENCIL_OP_INVERT:
      for (j = 0; j < QUAD_SIZE; j++) {
         if (mask & (1 << j)) {
            newstencil[j] = ~data->stencilVals[j];
         }
      }
      break;
   default:
      assert(0);
   }

   /*
    * update the stencil values
    */
   if (wrtMask != STENCIL_MAX) {
      /* apply bit-wise stencil buffer writemask */
      for (j = 0; j < QUAD_SIZE; j++) {
         data->stencilVals[j] = (wrtMask & newstencil[j]) | (~wrtMask & data->stencilVals[j]);
      }
   }
   else {
      for (j = 0; j < QUAD_SIZE; j++) {
         data->stencilVals[j] = newstencil[j];
      }
   }
}

   

/*
 * To increase efficiency, we should probably have multiple versions
 * of this function that are specifically for Z16, Z32 and FP Z buffers.
 * Try to effectively do that with codegen...
 */

static boolean
depth_test_quad(struct quad_stage *qs, 
                struct depth_data *data,
                struct quad_header *quad)
{
   struct softpipe_context *softpipe = qs->softpipe;
   unsigned zmask = 0;
   unsigned j;

   switch (softpipe->depth_stencil->depth.func) {
   case PIPE_FUNC_NEVER:
      /* zmask = 0 */
      break;
   case PIPE_FUNC_LESS:
      /* Note this is pretty much a single sse or cell instruction.  
       * Like this:  quad->mask &= (quad->outputs.depth < zzzz);
       */
      for (j = 0; j < QUAD_SIZE; j++) {
	 if (data->qzzzz[j] < data->bzzzz[j]) 
	    zmask |= 1 << j;
      }
      break;
   case PIPE_FUNC_EQUAL:
      for (j = 0; j < QUAD_SIZE; j++) {
	 if (data->qzzzz[j] == data->bzzzz[j]) 
	    zmask |= 1 << j;
      }
      break;
   case PIPE_FUNC_LEQUAL:
      for (j = 0; j < QUAD_SIZE; j++) {
	 if (data->qzzzz[j] <= data->bzzzz[j]) 
	    zmask |= (1 << j);
      }
      break;
   case PIPE_FUNC_GREATER:
      for (j = 0; j < QUAD_SIZE; j++) {
	 if (data->qzzzz[j] > data->bzzzz[j]) 
	    zmask |= (1 << j);
      }
      break;
   case PIPE_FUNC_NOTEQUAL:
      for (j = 0; j < QUAD_SIZE; j++) {
	 if (data->qzzzz[j] != data->bzzzz[j]) 
	    zmask |= (1 << j);
      }
      break;
   case PIPE_FUNC_GEQUAL:
      for (j = 0; j < QUAD_SIZE; j++) {
	 if (data->qzzzz[j] >= data->bzzzz[j]) 
	    zmask |= (1 << j);
      }
      break;
   case PIPE_FUNC_ALWAYS:
      zmask = MASK_ALL;
      break;
   default:
      assert(0);
   }

   quad->inout.mask &= zmask;
   if (quad->inout.mask == 0)
      return FALSE;

   /* Update our internal copy only if writemask set.  Even if
    * depth.writemask is FALSE, may still need to write out buffer
    * data due to stencil changes.
    */
   if (softpipe->depth_stencil->depth.writemask) {
      for (j = 0; j < QUAD_SIZE; j++) {
         if (quad->inout.mask & (1 << j)) {
            data->bzzzz[j] = data->qzzzz[j];
         }
      }
   }

   return TRUE;
}



/**
 * Do stencil (and depth) testing.  Stenciling depends on the outcome of
 * depth testing.
 */
static boolean
depth_stencil_test_quad(struct quad_stage *qs, 
                        struct depth_data *data,
                        struct quad_header *quad)
{
   struct softpipe_context *softpipe = qs->softpipe;
   unsigned func, zFailOp, zPassOp, failOp;
   ubyte ref, wrtMask, valMask;
   uint face = quad->input.facing;

   if (!softpipe->depth_stencil->stencil[1].enabled) {
      /* single-sided stencil test, use front (face=0) state */
      face = 0;
   }

   /* choose front or back face function, operator, etc */
   /* XXX we could do these initializations once per primitive */
   func    = softpipe->depth_stencil->stencil[face].func;
   failOp  = softpipe->depth_stencil->stencil[face].fail_op;
   zFailOp = softpipe->depth_stencil->stencil[face].zfail_op;
   zPassOp = softpipe->depth_stencil->stencil[face].zpass_op;
   ref     = softpipe->depth_stencil->stencil[face].ref_value;
   wrtMask = softpipe->depth_stencil->stencil[face].writemask;
   valMask = softpipe->depth_stencil->stencil[face].valuemask;


   /* do the stencil test first */
   {
      unsigned passMask, failMask;
      passMask = do_stencil_test(data, func, ref, valMask);
      failMask = quad->inout.mask & ~passMask;
      quad->inout.mask &= passMask;

      if (failOp != PIPE_STENCIL_OP_KEEP) {
         apply_stencil_op(data, failMask, failOp, ref, wrtMask);
      }
   }

   if (quad->inout.mask) {
      /* now the pixels that passed the stencil test are depth tested */
      if (softpipe->depth_stencil->depth.enabled) {
         const unsigned origMask = quad->inout.mask;

         depth_test_quad(qs, data, quad);  /* quad->mask is updated */

         /* update stencil buffer values according to z pass/fail result */
         if (zFailOp != PIPE_STENCIL_OP_KEEP) {
            const unsigned failMask = origMask & ~quad->inout.mask;
            apply_stencil_op(data, failMask, zFailOp, ref, wrtMask);
         }

         if (zPassOp != PIPE_STENCIL_OP_KEEP) {
            const unsigned passMask = origMask & quad->inout.mask;
            apply_stencil_op(data, passMask, zPassOp, ref, wrtMask);
         }
      }
      else {
         /* no depth test, apply Zpass operator to stencil buffer values */
         apply_stencil_op(data, quad->inout.mask, zPassOp, ref, wrtMask);
      }
   }

   return quad->inout.mask != 0;
}


#define ALPHATEST( FUNC, COMP )                                         \
   static int                                                          \
   alpha_test_quads_##FUNC( struct quad_stage *qs,                      \
                           struct quad_header *quads[],                 \
                           unsigned nr )                                \
   {                                                                    \
      const float ref = qs->softpipe->depth_stencil->alpha.ref_value;   \
      const uint cbuf = 0; /* only output[0].alpha is tested */         \
      unsigned pass_nr = 0;                                             \
      unsigned i;                                                       \
                                                                        \
      for (i = 0; i < nr; i++) {                                        \
         const float *aaaa = quads[i]->output.color[cbuf][3];           \
         unsigned passMask = 0;                                         \
                                                                        \
         if (aaaa[0] COMP ref) passMask |= (1 << 0);                    \
         if (aaaa[1] COMP ref) passMask |= (1 << 1);                    \
         if (aaaa[2] COMP ref) passMask |= (1 << 2);                    \
         if (aaaa[3] COMP ref) passMask |= (1 << 3);                    \
                                                                        \
         quads[i]->inout.mask &= passMask;                              \
                                                                        \
         if (quads[i]->inout.mask)                                      \
            quads[pass_nr++] = quads[i];                                \
      }                                                                 \
                                                                        \
      return pass_nr;                                                   \
   }


ALPHATEST( LESS,     < )
ALPHATEST( EQUAL,    == )
ALPHATEST( LEQUAL,   <= )
ALPHATEST( GREATER,  > )
ALPHATEST( NOTEQUAL, != )
ALPHATEST( GEQUAL,   >= )


/* XXX: Incorporate into shader using KILP.
 */
static int
alpha_test_quads(struct quad_stage *qs, 
                 struct quad_header *quads[], 
                 unsigned nr)
{
   switch (qs->softpipe->depth_stencil->alpha.func) {
   case PIPE_FUNC_LESS:
      return alpha_test_quads_LESS( qs, quads, nr );
   case PIPE_FUNC_EQUAL:
      return alpha_test_quads_EQUAL( qs, quads, nr );
      break;
   case PIPE_FUNC_LEQUAL:
      return alpha_test_quads_LEQUAL( qs, quads, nr );
   case PIPE_FUNC_GREATER:
      return alpha_test_quads_GREATER( qs, quads, nr );
   case PIPE_FUNC_NOTEQUAL:
      return alpha_test_quads_NOTEQUAL( qs, quads, nr );
   case PIPE_FUNC_GEQUAL:
      return alpha_test_quads_GEQUAL( qs, quads, nr );
   case PIPE_FUNC_ALWAYS:
      return nr;
   case PIPE_FUNC_NEVER:
   default:
      return 0;
   }
}

static unsigned mask_count[0x8] = 
{
   0,                           /* 0x0 */
   1,                           /* 0x1 */
   1,                           /* 0x2 */
   2,                           /* 0x3 */
   1,                           /* 0x4 */
   2,                           /* 0x5 */
   2,                           /* 0x6 */
   3,                           /* 0x7 */
};



static void
depth_test_quads_fallback(struct quad_stage *qs, 
                          struct quad_header *quads[],
                          unsigned nr)
{
   unsigned i, pass = 0;
   const struct sp_fragment_shader *fs = qs->softpipe->fs;
   boolean interp_depth = !fs->info.writes_z;
   struct depth_data data;


   if (qs->softpipe->depth_stencil->alpha.enabled) {
      nr = alpha_test_quads(qs, quads, nr);
   }

   if (qs->softpipe->framebuffer.zsbuf && 
       (qs->softpipe->depth_stencil->depth.enabled ||
        qs->softpipe->depth_stencil->stencil[0].enabled)) {

      data.ps = qs->softpipe->framebuffer.zsbuf;
      data.format = data.ps->format;
      data.tile = sp_get_cached_tile(qs->softpipe->zsbuf_cache, 
                                     quads[0]->input.x0, 
                                     quads[0]->input.y0);

      for (i = 0; i < nr; i++) {
         get_depth_stencil_values(&data, quads[i]);

         if (qs->softpipe->depth_stencil->depth.enabled) {
            if (interp_depth)
               interpolate_quad_depth(quads[i]);

            convert_quad_depth(&data, quads[i]);
         }

         if (qs->softpipe->depth_stencil->stencil[0].enabled) {
            if (!depth_stencil_test_quad(qs, &data, quads[i]))
               continue;
         }
         else {
            if (!depth_test_quad(qs, &data, quads[i]))
               continue;
         }

         if (qs->softpipe->depth_stencil->stencil[0].enabled ||
             qs->softpipe->depth_stencil->depth.writemask)
            write_depth_stencil_values(&data, quads[i]);

         qs->softpipe->occlusion_count += mask_count[quads[i]->inout.mask];
         quads[pass++] = quads[i];
      }

      nr = pass;
   }

   if (nr)
      qs->next->run(qs->next, quads, nr);
}

/* XXX: this function assumes setup function actually emits linear
 * spans of quads.  It seems a lot more natural to do (early)
 * depth-testing on spans rather than quads.
 */
static void
depth_interp_z16_less_write(struct quad_stage *qs, 
                            struct quad_header *quads[],
                            unsigned nr)
{
   unsigned i, pass = 0;
   const unsigned ix = quads[0]->input.x0;
   const unsigned iy = quads[0]->input.y0;
   const float fx = (float) ix;
   const float fy = (float) iy;
   const float dzdx = quads[0]->posCoef->dadx[2];
   const float dzdy = quads[0]->posCoef->dady[2];
   const float z0 = quads[0]->posCoef->a0[2] + dzdx * fx + dzdy * fy;
   struct softpipe_cached_tile *tile;
   ushort (*depth16)[TILE_SIZE];
   ushort idepth[4], depth_step;
   const float scale = 65535.0;

   idepth[0] = (ushort)((z0) * scale);
   idepth[1] = (ushort)((z0 + dzdx) * scale);
   idepth[2] = (ushort)((z0 + dzdy) * scale);
   idepth[3] = (ushort)((z0 + dzdx + dzdy) * scale);

   depth_step = (ushort)(dzdx * 2 * scale);

   tile = sp_get_cached_tile(qs->softpipe->zsbuf_cache, ix, iy);

   depth16 = (ushort (*)[TILE_SIZE])
      &tile->data.depth16[iy % TILE_SIZE][ix % TILE_SIZE];

   for (i = 0; i < nr; i++) {
      unsigned outmask = quads[i]->inout.mask;
      unsigned mask = 0;
      
      if ((outmask & 1) && idepth[0] < depth16[0][0]) {
         depth16[0][0] = idepth[0];
         mask |= (1 << 0);
      }

      if ((outmask & 2) && idepth[1] < depth16[0][1]) {
         depth16[0][1] = idepth[1];
         mask |= (1 << 1);
      }

      if ((outmask & 4) && idepth[2] < depth16[1][0]) {
         depth16[1][0] = idepth[2];
         mask |= (1 << 2);
      }

      if ((outmask & 8) && idepth[3] < depth16[1][1]) {
         depth16[1][1] = idepth[3];
         mask |= (1 << 3);
      }

      idepth[0] += depth_step;
      idepth[1] += depth_step;
      idepth[2] += depth_step;
      idepth[3] += depth_step;

      depth16 = (ushort (*)[TILE_SIZE]) &depth16[0][2];

      quads[i]->inout.mask = mask;
      if (quads[i]->inout.mask)
         quads[pass++] = quads[i];
   }

   if (pass)
      qs->next->run(qs->next, quads, pass);

}


static void
depth_noop(struct quad_stage *qs, 
           struct quad_header *quads[],
           unsigned nr)
{
   qs->next->run(qs->next, quads, nr);
}



static void
choose_depth_test(struct quad_stage *qs, 
                  struct quad_header *quads[],
                  unsigned nr)
{
   boolean interp_depth = !qs->softpipe->fs->info.writes_z;

   boolean alpha = qs->softpipe->depth_stencil->alpha.enabled;

   boolean depth = (qs->softpipe->framebuffer.zsbuf && 
                    qs->softpipe->depth_stencil->depth.enabled);

   unsigned depthfunc = qs->softpipe->depth_stencil->depth.func;

   boolean stencil = qs->softpipe->depth_stencil->stencil[0].enabled;

   boolean depthwrite = qs->softpipe->depth_stencil->depth.writemask;


   qs->run = depth_test_quads_fallback;

   if (!alpha &&
       !depth &&
       !stencil) {
      qs->run = depth_noop;
   }
   else if (!alpha && 
            interp_depth && 
            depth && 
            depthfunc == PIPE_FUNC_LESS && 
            depthwrite && 
            !stencil) 
   {
      switch (qs->softpipe->framebuffer.zsbuf->format) {
      case PIPE_FORMAT_Z16_UNORM:
         qs->run = depth_interp_z16_less_write;
         break;
      default:
         break;
      }
   }

   qs->run( qs, quads, nr );
}





static void depth_test_begin(struct quad_stage *qs)
{
   qs->run = choose_depth_test;
   qs->next->begin(qs->next);
}


static void depth_test_destroy(struct quad_stage *qs)
{
   FREE( qs );
}


struct quad_stage *sp_quad_depth_test_stage( struct softpipe_context *softpipe )
{
   struct quad_stage *stage = CALLOC_STRUCT(quad_stage);

   stage->softpipe = softpipe;
   stage->begin = depth_test_begin;
   stage->run = choose_depth_test;
   stage->destroy = depth_test_destroy;

   return stage;
}