mesa/swrast/s_span.c

/* $Id: s_span.c,v 1.9 2001/02/20 16:42:26 brianp Exp $ */

/*
 * Mesa 3-D graphics library
 * Version:  3.5
 *
 * Copyright (C) 1999-2001  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.
 */


/*
 * pixel span rasterization:
 * These functions implement the rasterization pipeline.
 */


#include "glheader.h"
#include "colormac.h"
#include "macros.h"
#include "mem.h"

#include "s_alpha.h"
#include "s_alphabuf.h"
#include "s_blend.h"
#include "s_context.h"
#include "s_depth.h"
#include "s_fog.h"
#include "s_logic.h"
#include "s_masking.h"
#include "s_scissor.h"
#include "s_span.h"
#include "s_stencil.h"
#include "s_texture.h"


/*
 * Apply the current polygon stipple pattern to a span of pixels.
 */
static void stipple_polygon_span( GLcontext *ctx,
                                  GLuint n, GLint x, GLint y, GLubyte mask[] )
{
   const GLuint highbit = 0x80000000;
   GLuint i, m, stipple;

   stipple = ctx->PolygonStipple[y % 32];
   m = highbit >> (GLuint) (x % 32);

   for (i = 0; i < n; i++) {
      if ((m & stipple) == 0) {
         mask[i] = 0;
      }
      m = m >> 1;
      if (m == 0) {
         m = highbit;
      }
   }
}


/*
 * Clip a pixel span to the current buffer/window boundaries.
 * Return:  'n' such that pixel 'n', 'n+1' etc. are clipped,
 *           as a special case:
 *           0 = all pixels clipped
 */
static GLuint clip_span( GLcontext *ctx,
                         GLint n, GLint x, GLint y, GLubyte mask[] )
{
   /* Clip to top and bottom */
   if (y < 0 || y >= ctx->DrawBuffer->Height) {
      return 0;
   }

   /* Clip to the left */
   if (x < 0) {
      if (x + n <= 0) {
         /* completely off left side */
         return 0;
      }
      else {
         /* partially off left side */
         BZERO(mask, -x * sizeof(GLubyte));
      }
   }

   /* Clip to right */
   if (x + n > ctx->DrawBuffer->Width) {
      if (x >= ctx->DrawBuffer->Width) {
         /* completely off right side */
         return 0;
      }
      else {
         /* partially off right side */
         return ctx->DrawBuffer->Width - x;
      }
   }

   return n;
}


/*
 * Draw to more than one color buffer (or none).
 */
static void multi_write_index_span( GLcontext *ctx, GLuint n,
                                    GLint x, GLint y, const GLuint indexes[],
                                    const GLubyte mask[] )
{
   GLuint bufferBit;

   if (ctx->Color.DrawBuffer == GL_NONE)
      return;

   /* loop over four possible dest color buffers */
   for (bufferBit = 1; bufferBit <= 8; bufferBit = bufferBit << 1) {
      if (bufferBit & ctx->Color.DrawDestMask) {
         GLuint indexTmp[MAX_WIDTH];
         ASSERT(n < MAX_WIDTH);

         if (bufferBit == FRONT_LEFT_BIT)
            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_FRONT_LEFT);
         else if (bufferBit == FRONT_RIGHT_BIT)
            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_FRONT_RIGHT);
         else if (bufferBit == BACK_LEFT_BIT)
            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_BACK_LEFT);
         else
            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_BACK_RIGHT);

         /* make copy of incoming indexes */
         MEMCPY( indexTmp, indexes, n * sizeof(GLuint) );
         if (ctx->Color.IndexLogicOpEnabled) {
            _mesa_logicop_ci_span( ctx, n, x, y, indexTmp, mask );
         }
         if (ctx->Color.IndexMask == 0) {
            break;
         }
         else if (ctx->Color.IndexMask != 0xffffffff) {
            _mesa_mask_index_span( ctx, n, x, y, indexTmp );
         }
         (*ctx->Driver.WriteCI32Span)( ctx, n, x, y, indexTmp, mask );
      }
   }

   /* restore default dest buffer */
   (void) (*ctx->Driver.SetDrawBuffer)( ctx, ctx->Color.DriverDrawBuffer);
}


/*
 * Write a horizontal span of color index pixels to the frame buffer.
 * Stenciling, Depth-testing, etc. are done as needed.
 * Input:  n - number of pixels in the span
 *         x, y - location of leftmost pixel in the span
 *         z - array of [n] z-values
 *         index - array of [n] color indexes
 *         primitive - either GL_POINT, GL_LINE, GL_POLYGON, or GL_BITMAP
 */
void gl_write_index_span( GLcontext *ctx,
                          GLuint n, GLint x, GLint y, const GLdepth z[],
			  const GLfixed fog[],
			  GLuint indexIn[], GLenum primitive )
{
   const GLuint modBits = FOG_BIT | BLEND_BIT | MASKING_BIT | LOGIC_OP_BIT;
   GLubyte mask[MAX_WIDTH];
   GLuint indexBackup[MAX_WIDTH];
   GLuint *index;  /* points to indexIn or indexBackup */
   SWcontext *swrast = SWRAST_CONTEXT(ctx);

   /* init mask to 1's (all pixels are to be written) */
   MEMSET(mask, 1, n);

   if ((swrast->_RasterMask & WINCLIP_BIT) || primitive==GL_BITMAP) {
      if ((n = clip_span(ctx,n,x,y,mask)) == 0) {
         return;
      }
   }

   if ((primitive==GL_BITMAP && (swrast->_RasterMask & modBits))
       || (swrast->_RasterMask & MULTI_DRAW_BIT)) {
      /* Make copy of color indexes */
      MEMCPY( indexBackup, indexIn, n * sizeof(GLuint) );
      index = indexBackup;
   }
   else {
      index = indexIn;
   }


   /* Do the scissor test */
   if (ctx->Scissor.Enabled) {
      if ((n = _mesa_scissor_span( ctx, n, x, y, mask )) == 0) {
         return;
      }
   }

   /* Polygon Stippling */
   if (ctx->Polygon.StippleFlag && primitive==GL_POLYGON) {
      stipple_polygon_span( ctx, n, x, y, mask );
   }

   if (ctx->Stencil.Enabled) {
      /* first stencil test */
      if (_mesa_stencil_and_ztest_span(ctx, n, x, y, z, mask) == GL_FALSE) {
         return;
      }
   }
   else if (ctx->Depth.Test) {
      /* regular depth testing */
      if (_mesa_depth_test_span( ctx, n, x, y, z, mask ) == 0)
         return;
   }

   /* if we get here, something passed the depth test */
   ctx->OcclusionResult = GL_TRUE;

   /* Per-pixel fog */
   if (ctx->Fog.Enabled) {
      if (fog && !swrast->_PreferPixelFog)
         _mesa_fog_ci_pixels( ctx, n, fog, index );
      else
         _mesa_depth_fog_ci_pixels( ctx, n, z, index );
   }

   if (swrast->_RasterMask & MULTI_DRAW_BIT) {
      /* draw to zero or two or more buffers */
      multi_write_index_span( ctx, n, x, y, index, mask );
   }
   else {
      /* normal situation: draw to exactly one buffer */
      if (ctx->Color.IndexLogicOpEnabled) {
         _mesa_logicop_ci_span( ctx, n, x, y, index, mask );
      }

      if (ctx->Color.IndexMask == 0) {
         return;
      }
      else if (ctx->Color.IndexMask != 0xffffffff) {
         _mesa_mask_index_span( ctx, n, x, y, index );
      }

      /* write pixels */
      (*ctx->Driver.WriteCI32Span)( ctx, n, x, y, index, mask );
   }
}


void gl_write_monoindex_span( GLcontext *ctx,
                              GLuint n, GLint x, GLint y,
			      const GLdepth z[],
			      const GLfixed fog[],
			      GLuint index, GLenum primitive )
{
   SWcontext *swrast = SWRAST_CONTEXT(ctx);
   GLubyte mask[MAX_WIDTH];
   GLuint i;

   /* init mask to 1's (all pixels are to be written) */
   MEMSET(mask, 1, n);

   if ((swrast->_RasterMask & WINCLIP_BIT) || primitive==GL_BITMAP) {
      if ((n = clip_span( ctx, n, x, y, mask)) == 0) {
	 return;
      }
   }

   /* Do the scissor test */
   if (ctx->Scissor.Enabled) {
      if ((n = _mesa_scissor_span( ctx, n, x, y, mask )) == 0) {
         return;
      }
   }

   /* Polygon Stippling */
   if (ctx->Polygon.StippleFlag && primitive==GL_POLYGON) {
      stipple_polygon_span( ctx, n, x, y, mask );
   }

   if (ctx->Stencil.Enabled) {
      /* first stencil test */
      if (_mesa_stencil_and_ztest_span(ctx, n, x, y, z, mask) == GL_FALSE) {
	 return;
      }
   }
   else if (ctx->Depth.Test) {
      /* regular depth testing */
      if (_mesa_depth_test_span( ctx, n, x, y, z, mask ) == 0)
         return;
   }

   /* if we get here, something passed the depth test */
   ctx->OcclusionResult = GL_TRUE;

   if (ctx->Color.DrawBuffer == GL_NONE) {
      /* write no pixels */
      return;
   }

   if (ctx->Fog.Enabled
       || ctx->Color.IndexLogicOpEnabled
       || ctx->Color.IndexMask != 0xffffffff) {
      /* different index per pixel */
      GLuint indexes[MAX_WIDTH];
      for (i = 0; i < n; i++) {
	 indexes[i] = index;
      }

      if (ctx->Fog.Enabled) {
 	 if (fog && !swrast->_PreferPixelFog)
 	    _mesa_fog_ci_pixels( ctx, n, fog, indexes );
 	 else
 	    _mesa_depth_fog_ci_pixels( ctx, n, z, indexes );
      }

      if (swrast->_RasterMask & MULTI_DRAW_BIT) {
         /* draw to zero or two or more buffers */
         multi_write_index_span( ctx, n, x, y, indexes, mask );
      }
      else {
         /* normal situation: draw to exactly one buffer */
         if (ctx->Color.IndexLogicOpEnabled) {
            _mesa_logicop_ci_span( ctx, n, x, y, indexes, mask );
         }
         if (ctx->Color.IndexMask == 0) {
            return;
         }
         else if (ctx->Color.IndexMask != 0xffffffff) {
            _mesa_mask_index_span( ctx, n, x, y, indexes );
         }
         (*ctx->Driver.WriteCI32Span)( ctx, n, x, y, indexes, mask );
      }
   }
   else {
      /* same color index for all pixels */
      ASSERT(!ctx->Color.IndexLogicOpEnabled);
      ASSERT(ctx->Color.IndexMask == 0xffffffff);
      if (swrast->_RasterMask & MULTI_DRAW_BIT) {
         /* draw to zero or two or more buffers */
         GLuint indexes[MAX_WIDTH];
         for (i = 0; i < n; i++)
            indexes[i] = index;
         multi_write_index_span( ctx, n, x, y, indexes, mask );
      }
      else {
         /* normal situation: draw to exactly one buffer */
         (*ctx->Driver.WriteMonoCISpan)( ctx, n, x, y, index, mask );
      }
   }
}


/*
 * Draw to more than one RGBA color buffer (or none).
 */
static void multi_write_rgba_span( GLcontext *ctx, GLuint n,
                                   GLint x, GLint y, CONST GLchan rgba[][4],
                                   const GLubyte mask[] )
{
   const GLuint colorMask = *((GLuint *) ctx->Color.ColorMask);
   GLuint bufferBit;
   SWcontext *swrast = SWRAST_CONTEXT(ctx);

   if (ctx->Color.DrawBuffer == GL_NONE)
      return;

   /* loop over four possible dest color buffers */
   for (bufferBit = 1; bufferBit <= 8; bufferBit = bufferBit << 1) {
      if (bufferBit & ctx->Color.DrawDestMask) {
         GLchan rgbaTmp[MAX_WIDTH][4];
         ASSERT(n < MAX_WIDTH);

         if (bufferBit == FRONT_LEFT_BIT) {
            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_FRONT_LEFT);
            ctx->DrawBuffer->Alpha = ctx->DrawBuffer->FrontLeftAlpha;
         }
         else if (bufferBit == FRONT_RIGHT_BIT) {
            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_FRONT_RIGHT);
            ctx->DrawBuffer->Alpha = ctx->DrawBuffer->FrontRightAlpha;
         }
         else if (bufferBit == BACK_LEFT_BIT) {
            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_BACK_LEFT);
            ctx->DrawBuffer->Alpha = ctx->DrawBuffer->BackLeftAlpha;
         }
         else {
            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_BACK_RIGHT);
            ctx->DrawBuffer->Alpha = ctx->DrawBuffer->BackRightAlpha;
         }

         /* make copy of incoming colors */
         MEMCPY( rgbaTmp, rgba, 4 * n * sizeof(GLchan) );

         if (ctx->Color.ColorLogicOpEnabled) {
            _mesa_logicop_rgba_span( ctx, n, x, y, rgbaTmp, mask );
         }
         else if (ctx->Color.BlendEnabled) {
            _mesa_blend_span( ctx, n, x, y, rgbaTmp, mask );
         }
         if (colorMask == 0x0) {
            break;
         }
         else if (colorMask != 0xffffffff) {
            _mesa_mask_rgba_span( ctx, n, x, y, rgbaTmp );
         }

         (*ctx->Driver.WriteRGBASpan)( ctx, n, x, y,
				       (const GLchan (*)[4]) rgbaTmp, mask );
         if (swrast->_RasterMask & ALPHABUF_BIT) {
            _mesa_write_alpha_span( ctx, n, x, y,
                                    (const GLchan (*)[4])rgbaTmp, mask );
         }
      }
   }

   /* restore default dest buffer */
   (void) (*ctx->Driver.SetDrawBuffer)( ctx, ctx->Color.DriverDrawBuffer );
}


void gl_write_rgba_span( GLcontext *ctx,
                         GLuint n, GLint x, GLint y, const GLdepth z[],
			 const GLfixed *fog,
                         GLchan rgbaIn[][4],
                         GLenum primitive )
{
   const GLuint modBits = FOG_BIT | BLEND_BIT | MASKING_BIT |
                          LOGIC_OP_BIT | TEXTURE_BIT;
   GLubyte mask[MAX_WIDTH];
   GLboolean write_all = GL_TRUE;
   GLchan rgbaBackup[MAX_WIDTH][4];
   GLchan (*rgba)[4];
   const GLubyte *Null = 0;
   SWcontext *swrast = SWRAST_CONTEXT(ctx);

   /* init mask to 1's (all pixels are to be written) */
   MEMSET(mask, 1, n);

   if ((swrast->_RasterMask & WINCLIP_BIT) || primitive==GL_BITMAP) {
      if ((n = clip_span( ctx,n,x,y,mask)) == 0) {
         return;
      }
      if (mask[0] == 0)
         write_all = GL_FALSE;
   }

   if ((primitive==GL_BITMAP && (swrast->_RasterMask & modBits))
       || (swrast->_RasterMask & MULTI_DRAW_BIT)) {
      /* must make a copy of the colors since they may be modified */
      MEMCPY( rgbaBackup, rgbaIn, 4 * n * sizeof(GLchan) );
      rgba = rgbaBackup;
   }
   else {
      rgba = rgbaIn;
   }

   /* Do the scissor test */
   if (ctx->Scissor.Enabled) {
      if ((n = _mesa_scissor_span( ctx, n, x, y, mask )) == 0) {
         return;
      }
      if (mask[0] == 0)
	write_all = GL_FALSE;
   }

   /* Polygon Stippling */
   if (ctx->Polygon.StippleFlag && primitive==GL_POLYGON) {
      stipple_polygon_span( ctx, n, x, y, mask );
      write_all = GL_FALSE;
   }

   /* Do the alpha test */
   if (ctx->Color.AlphaEnabled) {
      if (_mesa_alpha_test( ctx, n, (const GLchan (*)[4]) rgba, mask ) == 0) {
	 return;
      }
      write_all = GL_FALSE;
   }

   if (ctx->Stencil.Enabled) {
      /* first stencil test */
      if (_mesa_stencil_and_ztest_span(ctx, n, x, y, z, mask) == GL_FALSE) {
	 return;
      }
      write_all = GL_FALSE;
   }
   else if (ctx->Depth.Test) {
      /* regular depth testing */
      GLuint m = _mesa_depth_test_span( ctx, n, x, y, z, mask );
      if (m == 0) {
         return;
      }
      if (m < n) {
         write_all = GL_FALSE;
      }
   }

   /* if we get here, something passed the depth test */
   ctx->OcclusionResult = GL_TRUE;

   /* Per-pixel fog */
   if (ctx->Fog.Enabled) {
      if (fog && !swrast->_PreferPixelFog)
	 _mesa_fog_rgba_pixels( ctx, n, fog, rgba );
      else
	 _mesa_depth_fog_rgba_pixels( ctx, n, z, rgba );
   }

   if (swrast->_RasterMask & MULTI_DRAW_BIT) {
      multi_write_rgba_span( ctx, n, x, y, (const GLchan (*)[4]) rgba, mask );
   }
   else {
      /* normal: write to exactly one buffer */
      /* logic op or blending */
      const GLuint colorMask = *((GLuint *) ctx->Color.ColorMask);

      if (ctx->Color.ColorLogicOpEnabled) {
         _mesa_logicop_rgba_span( ctx, n, x, y, rgba, mask );
      }
      else if (ctx->Color.BlendEnabled) {
         _mesa_blend_span( ctx, n, x, y, rgba, mask );
      }

      /* Color component masking */
      if (colorMask == 0x0) {
         return;
      }
      else if (colorMask != 0xffffffff) {
         _mesa_mask_rgba_span( ctx, n, x, y, rgba );
      }

      /* write pixels */
      (*ctx->Driver.WriteRGBASpan)( ctx, n, x, y,
				    (const GLchan (*)[4]) rgba,
				    write_all ? Null : mask );

      if (swrast->_RasterMask & ALPHABUF_BIT) {
         _mesa_write_alpha_span( ctx, n, x, y,
                                 (const GLchan (*)[4]) rgba,
                                 write_all ? Null : mask );
      }
   }
}


/*
 * Write a horizontal span of color pixels to the frame buffer.
 * The color is initially constant for the whole span.
 * Alpha-testing, stenciling, depth-testing, and blending are done as needed.
 * Input:  n - number of pixels in the span
 *         x, y - location of leftmost pixel in the span
 *         z - array of [n] z-values
 *         r, g, b, a - the color of the pixels
 *         primitive - either GL_POINT, GL_LINE, GL_POLYGON or GL_BITMAP.
 */
void gl_write_monocolor_span( GLcontext *ctx,
                              GLuint n, GLint x, GLint y, const GLdepth z[],
			      const GLfixed fog[],
			      const GLchan color[4],
                              GLenum primitive )
{
   const GLuint colorMask = *((GLuint *) ctx->Color.ColorMask);
   GLuint i;
   GLubyte mask[MAX_WIDTH];
   GLboolean write_all = GL_TRUE;
   GLchan rgba[MAX_WIDTH][4];
   const GLubyte *Null = 0;
   SWcontext *swrast = SWRAST_CONTEXT(ctx);

   /* init mask to 1's (all pixels are to be written) */
   MEMSET(mask, 1, n);

   if ((swrast->_RasterMask & WINCLIP_BIT) || primitive==GL_BITMAP) {
      if ((n = clip_span( ctx,n,x,y,mask)) == 0) {
	 return;
      }
      if (mask[0] == 0)
         write_all = GL_FALSE;
   }

   /* Do the scissor test */
   if (ctx->Scissor.Enabled) {
      if ((n = _mesa_scissor_span( ctx, n, x, y, mask )) == 0) {
         return;
      }
      if (mask[0] == 0)
         write_all = GL_FALSE;
   }

   /* Polygon Stippling */
   if (ctx->Polygon.StippleFlag && primitive==GL_POLYGON) {
      stipple_polygon_span( ctx, n, x, y, mask );
      write_all = GL_FALSE;
   }

   /* Do the alpha test */
   if (ctx->Color.AlphaEnabled) {
      for (i = 0; i < n; i++) {
         rgba[i][ACOMP] = color[ACOMP];
      }
      if (_mesa_alpha_test( ctx, n, (const GLchan (*)[4])rgba, mask ) == 0) {
	 return;
      }
      write_all = GL_FALSE;
   }

   if (ctx->Stencil.Enabled) {
      /* first stencil test */
      if (_mesa_stencil_and_ztest_span(ctx, n, x, y, z, mask) == GL_FALSE) {
	 return;
      }
      write_all = GL_FALSE;
   }
   else if (ctx->Depth.Test) {
      /* regular depth testing */
      GLuint m = _mesa_depth_test_span( ctx, n, x, y, z, mask );
      if (m == 0) {
         return;
      }
      if (m < n) {
         write_all = GL_FALSE;
      }
   }

   /* if we get here, something passed the depth test */
   ctx->OcclusionResult = GL_TRUE;

   if (ctx->Color.DrawBuffer == GL_NONE) {
      /* write no pixels */
      return;
   }

   if (ctx->Color.ColorLogicOpEnabled || colorMask != 0xffffffff ||
       (swrast->_RasterMask & (BLEND_BIT | FOG_BIT))) {
      /* assign same color to each pixel */
      for (i = 0; i < n; i++) {
	 if (mask[i]) {
            COPY_CHAN4(rgba[i], color);
	 }
      }

      /* Per-pixel fog */
      if (ctx->Fog.Enabled) {
	 if (fog && !swrast->_PreferPixelFog)
	    _mesa_fog_rgba_pixels( ctx, n, fog, rgba );
	 else
	    _mesa_depth_fog_rgba_pixels( ctx, n, z, rgba );
      }

      if (swrast->_RasterMask & MULTI_DRAW_BIT) {
         multi_write_rgba_span( ctx, n, x, y,
                                (const GLchan (*)[4]) rgba, mask );
      }
      else {
         /* normal: write to exactly one buffer */
         if (ctx->Color.ColorLogicOpEnabled) {
            _mesa_logicop_rgba_span( ctx, n, x, y, rgba, mask );
         }
         else if (ctx->Color.BlendEnabled) {
            _mesa_blend_span( ctx, n, x, y, rgba, mask );
         }

         /* Color component masking */
         if (colorMask == 0x0) {
            return;
         }
         else if (colorMask != 0xffffffff) {
            _mesa_mask_rgba_span( ctx, n, x, y, rgba );
         }

         /* write pixels */
         (*ctx->Driver.WriteRGBASpan)( ctx, n, x, y,
				       (const GLchan (*)[4]) rgba,
				       write_all ? Null : mask );
         if (swrast->_RasterMask & ALPHABUF_BIT) {
            _mesa_write_alpha_span( ctx, n, x, y,
                                    (const GLchan (*)[4]) rgba,
                                    write_all ? Null : mask );
         }
      }
   }
   else {
      /* same color for all pixels */
      ASSERT(!ctx->Color.BlendEnabled);
      ASSERT(!ctx->Color.ColorLogicOpEnabled);

      if (swrast->_RasterMask & MULTI_DRAW_BIT) {
         for (i = 0; i < n; i++) {
            if (mask[i]) {
               COPY_CHAN4(rgba[i], color);
            }
         }
         multi_write_rgba_span( ctx, n, x, y,
				(const GLchan (*)[4]) rgba, mask );
      }
      else {
         (*ctx->Driver.WriteMonoRGBASpan)( ctx, n, x, y, color, mask );
         if (swrast->_RasterMask & ALPHABUF_BIT) {
            _mesa_write_mono_alpha_span( ctx, n, x, y, (GLchan) color[ACOMP],
                                         write_all ? Null : mask );
         }
      }
   }
}


/*
 * Add specular color to base color.  This is used only when
 * GL_LIGHT_MODEL_COLOR_CONTROL = GL_SEPARATE_SPECULAR_COLOR.
 */
static void add_colors(GLuint n, GLchan rgba[][4], CONST GLchan specular[][4] )
{
   GLuint i;
   for (i = 0; i < n; i++) {
      GLint r = rgba[i][RCOMP] + specular[i][RCOMP];
      GLint g = rgba[i][GCOMP] + specular[i][GCOMP];
      GLint b = rgba[i][BCOMP] + specular[i][BCOMP];
      rgba[i][RCOMP] = (GLchan) MIN2(r, CHAN_MAX);
      rgba[i][GCOMP] = (GLchan) MIN2(g, CHAN_MAX);
      rgba[i][BCOMP] = (GLchan) MIN2(b, CHAN_MAX);
   }
}


/*
 * Write a horizontal span of textured pixels to the frame buffer.
 * The color of each pixel is different.
 * Alpha-testing, stenciling, depth-testing, and blending are done
 * as needed.
 * Input:  n - number of pixels in the span
 *         x, y - location of leftmost pixel in the span
 *         z - array of [n] z-values
 *         s, t - array of (s,t) texture coordinates for each pixel
 *         lambda - array of texture lambda values
 *         rgba - array of [n] color components
 *         primitive - either GL_POINT, GL_LINE, GL_POLYGON or GL_BITMAP.
 */
void gl_write_texture_span( GLcontext *ctx,
                            GLuint n, GLint x, GLint y, const GLdepth z[],
			    const GLfixed fog[],
			    const GLfloat s[], const GLfloat t[],
                            const GLfloat u[], GLfloat lambda[],
			    GLchan rgbaIn[][4], CONST GLchan spec[][4],
			    GLenum primitive )
{
   const GLuint colorMask = *((GLuint *) ctx->Color.ColorMask);
   GLubyte mask[MAX_WIDTH];
   GLboolean write_all = GL_TRUE;
   GLchan rgbaBackup[MAX_WIDTH][4];
   GLchan (*rgba)[4];   /* points to either rgbaIn or rgbaBackup */
   const GLubyte *Null = 0;
   SWcontext *swrast = SWRAST_CONTEXT(ctx);

   /* init mask to 1's (all pixels are to be written) */
   MEMSET(mask, 1, n);

   if ((swrast->_RasterMask & WINCLIP_BIT) || primitive==GL_BITMAP) {
      if ((n=clip_span(ctx, n, x, y, mask)) == 0) {
	 return;
      }
      if (mask[0] == 0)
	write_all = GL_FALSE;
   }


   if (primitive==GL_BITMAP || (swrast->_RasterMask & MULTI_DRAW_BIT)) {
      /* must make a copy of the colors since they may be modified */
      MEMCPY(rgbaBackup, rgbaIn, 4 * n * sizeof(GLchan));
      rgba = rgbaBackup;
   }
   else {
      rgba = rgbaIn;
   }

   /* Do the scissor test */
   if (ctx->Scissor.Enabled) {
      if ((n = _mesa_scissor_span( ctx, n, x, y, mask )) == 0) {
         return;
      }
      if (mask[0] == 0)
         write_all = GL_FALSE;
   }

   /* Polygon Stippling */
   if (ctx->Polygon.StippleFlag && primitive==GL_POLYGON) {
      stipple_polygon_span( ctx, n, x, y, mask );
      write_all = GL_FALSE;
   }

   /* Texture with alpha test*/
   if (ctx->Color.AlphaEnabled) {
      /* Texturing without alpha is done after depth-testing which
         gives a potential speed-up. */
      ASSERT(ctx->Texture._ReallyEnabled);
      _swrast_texture_fragments( ctx, 0, n, s, t, u, lambda,
                                 (CONST GLchan (*)[4]) rgba, rgba );

      /* Do the alpha test */
      if (_mesa_alpha_test( ctx, n, (const GLchan (*)[4]) rgba, mask ) == 0) {
         return;
      }
      write_all = GL_FALSE;
   }

   if (ctx->Stencil.Enabled) {
      /* first stencil test */
      if (_mesa_stencil_and_ztest_span(ctx, n, x, y, z, mask) == GL_FALSE) {
	 return;
      }
      write_all = GL_FALSE;
   }
   else if (ctx->Depth.Test) {
      /* regular depth testing */
      GLuint m = _mesa_depth_test_span( ctx, n, x, y, z, mask );
      if (m == 0) {
         return;
      }
      if (m < n) {
         write_all = GL_FALSE;
      }
   }

   /* if we get here, something passed the depth test */
   ctx->OcclusionResult = GL_TRUE;

   /* Texture without alpha test */
   if (! ctx->Color.AlphaEnabled) {
      ASSERT(ctx->Texture._ReallyEnabled);
      _swrast_texture_fragments( ctx, 0, n, s, t, u, lambda,
                                 (CONST GLchan (*)[4]) rgba, rgba );
   }

   /* Add base and specular colors */
   if (spec &&
       (ctx->Fog.ColorSumEnabled ||
	(ctx->Light.Enabled && ctx->Light.Model.ColorControl == GL_SEPARATE_SPECULAR_COLOR)))
     add_colors( n, rgba, spec );   /* rgba = rgba + spec */

   /* Per-pixel fog */
   if (ctx->Fog.Enabled) {
      if (fog && !swrast->_PreferPixelFog)
	 _mesa_fog_rgba_pixels( ctx, n, fog, rgba );
      else
	 _mesa_depth_fog_rgba_pixels( ctx, n, z, rgba );
   }

   if (swrast->_RasterMask & MULTI_DRAW_BIT) {
      multi_write_rgba_span( ctx, n, x, y, (const GLchan (*)[4]) rgba, mask );
   }
   else {
      /* normal: write to exactly one buffer */
      if (ctx->Color.ColorLogicOpEnabled) {
         _mesa_logicop_rgba_span( ctx, n, x, y, rgba, mask );
      }
      else  if (ctx->Color.BlendEnabled) {
         _mesa_blend_span( ctx, n, x, y, rgba, mask );
      }
      if (colorMask == 0x0) {
         return;
      }
      else if (colorMask != 0xffffffff) {
         _mesa_mask_rgba_span( ctx, n, x, y, rgba );
      }

      (*ctx->Driver.WriteRGBASpan)( ctx, n, x, y, (const GLchan (*)[4])rgba,
				    write_all ? Null : mask );
      if (swrast->_RasterMask & ALPHABUF_BIT) {
         _mesa_write_alpha_span( ctx, n, x, y, (const GLchan (*)[4]) rgba,
                                 write_all ? Null : mask );
      }
   }
}


/*
 * As above but perform multiple stages of texture application.
 */
void
gl_write_multitexture_span( GLcontext *ctx,
                            GLuint n, GLint x, GLint y,
                            const GLdepth z[],
			    const GLfixed fog[],
                            CONST GLfloat s[MAX_TEXTURE_UNITS][MAX_WIDTH],
                            CONST GLfloat t[MAX_TEXTURE_UNITS][MAX_WIDTH],
                            CONST GLfloat u[MAX_TEXTURE_UNITS][MAX_WIDTH],
                            GLfloat lambda[][MAX_WIDTH],
                            GLchan rgbaIn[MAX_TEXTURE_UNITS][4],
                            CONST GLchan spec[MAX_TEXTURE_UNITS][4],
                            GLenum primitive )
{
   GLubyte mask[MAX_WIDTH];
   GLboolean write_all = GL_TRUE;
   GLchan rgbaBackup[MAX_WIDTH][4];
   GLchan (*rgba)[4];   /* points to either rgbaIn or rgbaBackup */
   GLuint i;
   const GLubyte *Null = 0;
   const GLuint texUnits = ctx->Const.MaxTextureUnits;
   SWcontext *swrast = SWRAST_CONTEXT(ctx);

   /* init mask to 1's (all pixels are to be written) */
   MEMSET(mask, 1, n);

   if ((swrast->_RasterMask & WINCLIP_BIT) || primitive==GL_BITMAP) {
      if ((n=clip_span(ctx, n, x, y, mask)) == 0) {
	 return;
      }
      if (mask[0] == 0)
	write_all = GL_FALSE;
   }


   if (primitive==GL_BITMAP || (swrast->_RasterMask & MULTI_DRAW_BIT)
                            || texUnits > 1) {
      /* must make a copy of the colors since they may be modified */
      MEMCPY(rgbaBackup, rgbaIn, 4 * n * sizeof(GLchan));
      rgba = rgbaBackup;
   }
   else {
      rgba = rgbaIn;
   }

   /* Do the scissor test */
   if (ctx->Scissor.Enabled) {
      if ((n = _mesa_scissor_span( ctx, n, x, y, mask )) == 0) {
         return;
      }
      if (mask[0] == 0)
         write_all = GL_FALSE;
   }

   /* Polygon Stippling */
   if (ctx->Polygon.StippleFlag && primitive==GL_POLYGON) {
      stipple_polygon_span( ctx, n, x, y, mask );
      write_all = GL_FALSE;
   }

   /* Texture with alpha test*/
   if (ctx->Color.AlphaEnabled) {
      /* Texturing without alpha is done after depth-testing which
       * gives a potential speed-up.
       */
      ASSERT(ctx->Texture._ReallyEnabled);
      for (i = 0; i < texUnits; i++)
         _swrast_texture_fragments( ctx, i, n, s[i], t[i], u[i], lambda[i],
                                    (CONST GLchan (*)[4]) rgbaIn, rgba );

      /* Do the alpha test */
      if (_mesa_alpha_test( ctx, n, (const GLchan (*)[4])rgba, mask ) == 0) {
         return;
      }
      write_all = GL_FALSE;
   }

   if (ctx->Stencil.Enabled) {
      /* first stencil test */
      if (_mesa_stencil_and_ztest_span(ctx, n, x, y, z, mask) == GL_FALSE) {
	 return;
      }
      write_all = GL_FALSE;
   }
   else if (ctx->Depth.Test) {
      /* regular depth testing */
      GLuint m = _mesa_depth_test_span( ctx, n, x, y, z, mask );
      if (m == 0) {
         return;
      }
      if (m < n) {
         write_all = GL_FALSE;
      }
   }

   /* if we get here, something passed the depth test */
   ctx->OcclusionResult = GL_TRUE;

   /* Texture without alpha test */
   if (! ctx->Color.AlphaEnabled) {
      ASSERT(ctx->Texture._ReallyEnabled);
      for (i = 0; i < texUnits; i++)
         _swrast_texture_fragments( ctx, i, n, s[i], t[i], u[i], lambda[i],
                                    (CONST GLchan (*)[4]) rgbaIn, rgba );
   }

   /* Add base and specular colors */
   if (spec &&
       (ctx->Fog.ColorSumEnabled ||
	(ctx->Light.Enabled &&
	 ctx->Light.Model.ColorControl == GL_SEPARATE_SPECULAR_COLOR)))
      add_colors( n, rgba, spec );   /* rgba = rgba + spec */

   /* Per-pixel fog */
   if (ctx->Fog.Enabled) {
      if (fog && !swrast->_PreferPixelFog)
	 _mesa_fog_rgba_pixels( ctx, n, fog, rgba );
      else
	 _mesa_depth_fog_rgba_pixels( ctx, n, z, rgba );
   }

   if (swrast->_RasterMask & MULTI_DRAW_BIT) {
      multi_write_rgba_span( ctx, n, x, y, (const GLchan (*)[4]) rgba, mask );
   }
   else {
      /* normal: write to exactly one buffer */
      const GLuint colorMask = *((GLuint *) ctx->Color.ColorMask);

      if (ctx->Color.ColorLogicOpEnabled) {
         _mesa_logicop_rgba_span( ctx, n, x, y, rgba, mask );
      }
      else  if (ctx->Color.BlendEnabled) {
         _mesa_blend_span( ctx, n, x, y, rgba, mask );
      }

      if (colorMask == 0x0) {
         return;
      }
      else if (colorMask != 0xffffffff) {
         _mesa_mask_rgba_span( ctx, n, x, y, rgba );
      }

      (*ctx->Driver.WriteRGBASpan)( ctx, n, x, y, (const GLchan (*)[4])rgba,
                                    write_all ? Null : mask );
      if (swrast->_RasterMask & ALPHABUF_BIT) {
         _mesa_write_alpha_span( ctx, n, x, y, (const GLchan (*)[4])rgba,
                                 write_all ? Null : mask );
      }
   }
}


/*
 * Read RGBA pixels from frame buffer.  Clipping will be done to prevent
 * reading ouside the buffer's boundaries.
 */
void gl_read_rgba_span( GLcontext *ctx, GLframebuffer *buffer,
                        GLuint n, GLint x, GLint y,
                        GLchan rgba[][4] )
{
   if (y < 0 || y >= buffer->Height
       || x + (GLint) n < 0 || x >= buffer->Width) {
      /* completely above, below, or right */
      /* XXX maybe leave undefined? */
      BZERO(rgba, 4 * n * sizeof(GLchan));
   }
   else {
      GLint skip, length;
      if (x < 0) {
         /* left edge clippping */
         skip = -x;
         length = (GLint) n - skip;
         if (length < 0) {
            /* completely left of window */
            return;
         }
         if (length > buffer->Width) {
            length = buffer->Width;
         }
      }
      else if ((GLint) (x + n) > buffer->Width) {
         /* right edge clipping */
         skip = 0;
         length = buffer->Width - x;
         if (length < 0) {
            /* completely to right of window */
            return;
         }
      }
      else {
         /* no clipping */
         skip = 0;
         length = (GLint) n;
      }

      (*ctx->Driver.ReadRGBASpan)( ctx, length, x + skip, y, rgba + skip );
      if (buffer->UseSoftwareAlphaBuffers) {
         _mesa_read_alpha_span( ctx, length, x + skip, y, rgba + skip );
      }
   }
}


/*
 * Read CI pixels from frame buffer.  Clipping will be done to prevent
 * reading ouside the buffer's boundaries.
 */
void gl_read_index_span( GLcontext *ctx, GLframebuffer *buffer,
                         GLuint n, GLint x, GLint y, GLuint indx[] )
{
   if (y < 0 || y >= buffer->Height
       || x + (GLint) n < 0 || x >= buffer->Width) {
      /* completely above, below, or right */
      BZERO(indx, n * sizeof(GLuint));
   }
   else {
      GLint skip, length;
      if (x < 0) {
         /* left edge clippping */
         skip = -x;
         length = (GLint) n - skip;
         if (length < 0) {
            /* completely left of window */
            return;
         }
         if (length > buffer->Width) {
            length = buffer->Width;
         }
      }
      else if ((GLint) (x + n) > buffer->Width) {
         /* right edge clipping */
         skip = 0;
         length = buffer->Width - x;
         if (length < 0) {
            /* completely to right of window */
            return;
         }
      }
      else {
         /* no clipping */
         skip = 0;
         length = (GLint) n;
      }

      (*ctx->Driver.ReadCI32Span)( ctx, length, skip + x, y, indx + skip );
   }
}