Overhaul of glRead/DrawBuffer() code. Now, swrast->Driver.SetBuffer()

indicates the read AND draw color buffer for all software rasterization.
Lots of related clean-ups.  See RELNOTES-4.1 for details.

11 files changed, 244 insertions, 196 deletions

diff --git a/src/mesa/swrast/s_accum.c b/src/mesa/swrast/s_accum.c
index 09c4d8647b0..0159304c172 100644
--- a/src/mesa/swrast/s_accum.c
+++ b/src/mesa/swrast/s_accum.c
@@ -1,4 +1,4 @@
-/* $Id: s_accum.c,v 1.17 2002/06/15 02:38:17 brianp Exp $ */
+/* $Id: s_accum.c,v 1.18 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -306,8 +306,7 @@ _swrast_Accum( GLcontext *ctx, GLenum op, GLfloat value,
          if (value == 0.0F)
             return;
 
-         (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-					  ctx->Pixel.DriverReadBuffer );
+         _swrast_use_read_buffer(ctx);
 
          /* May have to leave optimized accum buffer mode */
          if (swrast->_IntegerAccumScaler == 0.0 && value > 0.0 && value <= 1.0)
@@ -359,14 +358,13 @@ _swrast_Accum( GLcontext *ctx, GLenum op, GLfloat value,
             }
          }
          /* restore read buffer = draw buffer (the default) */
-         (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer,
-					  ctx->Color.DriverDrawBuffer );
+         _swrast_use_draw_buffer(ctx);
+
          RENDER_FINISH(swrast,ctx);
 	 break;
 
       case GL_LOAD:
-         (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-					  ctx->Pixel.DriverReadBuffer );
+         _swrast_use_read_buffer(ctx);
 
          /* This is a change to go into optimized accum buffer mode */
          if (value > 0.0 && value <= 1.0) {
@@ -433,8 +431,8 @@ _swrast_Accum( GLcontext *ctx, GLenum op, GLfloat value,
          }
 
          /* restore read buffer = draw buffer (the default) */
-         (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer,
-                                       ctx->Color.DriverDrawBuffer );
+         _swrast_use_draw_buffer(ctx);
+
          RENDER_FINISH(swrast,ctx);
 	 break;
 
diff --git a/src/mesa/swrast/s_alphabuf.c b/src/mesa/swrast/s_alphabuf.c
index 56c4d552da2..b303c0fc76c 100644
--- a/src/mesa/swrast/s_alphabuf.c
+++ b/src/mesa/swrast/s_alphabuf.c
@@ -1,4 +1,4 @@
-/* $Id: s_alphabuf.c,v 1.10 2002/03/19 16:47:05 brianp Exp $ */
+/* $Id: s_alphabuf.c,v 1.11 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -38,20 +38,12 @@
 #include "s_alphabuf.h"
 
 
-#define ALPHA_DRAW_ADDR(X,Y) \
-   (ctx->DrawBuffer->Alpha + (Y) * ctx->DrawBuffer->Width + (X))
-
-#define ALPHA_READ_ADDR(X,Y) \
-   (ctx->ReadBuffer->Alpha + (Y) * ctx->ReadBuffer->Width + (X))
-
-
 /*
  * Allocate a new front and back alpha buffer.
  */
 void
 _mesa_alloc_alpha_buffers( GLframebuffer *buffer )
 {
-   GET_CURRENT_CONTEXT(ctx);
    const GLint bytes = buffer->Width * buffer->Height * sizeof(GLchan);
 
    ASSERT(buffer->UseSoftwareAlphaBuffers);
@@ -101,17 +93,6 @@ _mesa_alloc_alpha_buffers( GLframebuffer *buffer )
          }
       }
    }
-
-   if (ctx) {
-      if (ctx->Color.DriverDrawBuffer == GL_FRONT_LEFT)
-         buffer->Alpha = buffer->FrontLeftAlpha;
-      else if (ctx->Color.DriverDrawBuffer == GL_BACK_LEFT)
-         buffer->Alpha = buffer->BackLeftAlpha;
-      else if (ctx->Color.DriverDrawBuffer == GL_FRONT_RIGHT)
-         buffer->Alpha = buffer->FrontRightAlpha;
-      else if (ctx->Color.DriverDrawBuffer == GL_BACK_RIGHT)
-         buffer->Alpha = buffer->BackRightAlpha;
-   }
 }
 
 
@@ -129,7 +110,7 @@ _mesa_clear_alpha_buffers( GLcontext *ctx )
 
    /* loop over four possible alpha buffers */
    for (bufferBit = 1; bufferBit <= 8; bufferBit = bufferBit << 1) {
-      if (bufferBit & ctx->Color.DrawDestMask) {
+      if (bufferBit & ctx->Color._DrawDestMask) {
          GLchan *buffer;
          if (bufferBit == FRONT_LEFT_BIT) {
             buffer = ctx->DrawBuffer->FrontLeftAlpha;
@@ -187,13 +168,39 @@ _mesa_clear_alpha_buffers( GLcontext *ctx )
 
 
 
+static INLINE
+GLchan *get_alpha_buffer( GLcontext *ctx )
+{
+   switch (ctx->Color._DriverDrawBuffer) {
+   case GL_FRONT_LEFT:
+      return ctx->DrawBuffer->FrontLeftAlpha;
+      break;
+   case GL_BACK_LEFT:
+      return ctx->DrawBuffer->BackLeftAlpha;
+      break;
+   case GL_FRONT_RIGHT:
+      return ctx->DrawBuffer->FrontRightAlpha;
+      break;
+   case GL_BACK_RIGHT:
+      return ctx->DrawBuffer->BackRightAlpha;
+      break;
+   default:
+      _mesa_problem(ctx, "Bad DriverDrawBuffer in _mesa_write_alpha_span()");
+      return ctx->DrawBuffer->FrontLeftAlpha; /* aribitrary */
+   }
+}
+
+
 void
 _mesa_write_alpha_span( GLcontext *ctx, GLuint n, GLint x, GLint y,
                         CONST GLchan rgba[][4], const GLubyte mask[] )
 {
-   GLchan *aptr = ALPHA_DRAW_ADDR( x, y );
+   GLchan *buffer, *aptr;
    GLuint i;
 
+   buffer = get_alpha_buffer(ctx);
+   aptr = buffer + y * ctx->DrawBuffer->Width + x;
+
    if (mask) {
       for (i=0;i<n;i++) {
          if (mask[i]) {
@@ -214,9 +221,12 @@ void
 _mesa_write_mono_alpha_span( GLcontext *ctx, GLuint n, GLint x, GLint y,
                              GLchan alpha, const GLubyte mask[] )
 {
-   GLchan *aptr = ALPHA_DRAW_ADDR( x, y );
+   GLchan *buffer, *aptr;
    GLuint i;
 
+   buffer = get_alpha_buffer(ctx);
+   aptr = buffer + y * ctx->DrawBuffer->Width + x;
+
    if (mask) {
       for (i=0;i<n;i++) {
          if (mask[i]) {
@@ -238,19 +248,22 @@ _mesa_write_alpha_pixels( GLcontext *ctx,
                           GLuint n, const GLint x[], const GLint y[],
                           CONST GLchan rgba[][4], const GLubyte mask[] )
 {
+   GLchan *buffer;
    GLuint i;
 
+   buffer = get_alpha_buffer(ctx);
+
    if (mask) {
       for (i=0;i<n;i++) {
          if (mask[i]) {
-            GLchan *aptr = ALPHA_DRAW_ADDR( x[i], y[i] );
+            GLchan *aptr = buffer + y[i] * ctx->DrawBuffer->Width + x[i];
             *aptr = rgba[i][ACOMP];
          }
       }
    }
    else {
       for (i=0;i<n;i++) {
-         GLchan *aptr = ALPHA_DRAW_ADDR( x[i], y[i] );
+         GLchan *aptr = buffer + y[i] * ctx->DrawBuffer->Width + x[i];
          *aptr = rgba[i][ACOMP];
       }
    }
@@ -262,19 +275,22 @@ _mesa_write_mono_alpha_pixels( GLcontext *ctx,
                                GLuint n, const GLint x[], const GLint y[],
                                GLchan alpha, const GLubyte mask[] )
 {
+   GLchan *buffer;
    GLuint i;
 
+   buffer = get_alpha_buffer(ctx);
+
    if (mask) {
       for (i=0;i<n;i++) {
          if (mask[i]) {
-            GLchan *aptr = ALPHA_DRAW_ADDR( x[i], y[i] );
+            GLchan *aptr = buffer + y[i] * ctx->DrawBuffer->Width + x[i];
             *aptr = alpha;
          }
       }
    }
    else {
       for (i=0;i<n;i++) {
-         GLchan *aptr = ALPHA_DRAW_ADDR( x[i], y[i] );
+         GLchan *aptr = buffer + y[i] * ctx->DrawBuffer->Width + x[i];
          *aptr = alpha;
       }
    }
@@ -286,11 +302,14 @@ void
 _mesa_read_alpha_span( GLcontext *ctx,
                        GLuint n, GLint x, GLint y, GLchan rgba[][4] )
 {
-   GLchan *aptr = ALPHA_READ_ADDR( x, y );
+   const GLchan *buffer, *aptr;
    GLuint i;
-   for (i=0;i<n;i++) {
+
+   buffer = get_alpha_buffer(ctx);
+   aptr = buffer + y * ctx->DrawBuffer->Width + x;
+
+   for (i = 0; i < n; i++)
       rgba[i][ACOMP] = *aptr++;
-   }
 }
 
 
@@ -299,10 +318,14 @@ _mesa_read_alpha_pixels( GLcontext *ctx,
                          GLuint n, const GLint x[], const GLint y[],
                          GLchan rgba[][4], const GLubyte mask[] )
 {
+   const GLchan *buffer;
    GLuint i;
-   for (i=0;i<n;i++) {
+
+   buffer = get_alpha_buffer(ctx);
+
+   for (i = 0; i < n; i++) {
       if (mask[i]) {
-         GLchan *aptr = ALPHA_READ_ADDR( x[i], y[i] );
+         const GLchan *aptr = buffer + y[i] * ctx->DrawBuffer->Width + x[i];
          rgba[i][ACOMP] = *aptr;
       }
    }
diff --git a/src/mesa/swrast/s_buffers.c b/src/mesa/swrast/s_buffers.c
index 6c7b447aba8..dcfa26f5e20 100644
--- a/src/mesa/swrast/s_buffers.c
+++ b/src/mesa/swrast/s_buffers.c
@@ -1,4 +1,4 @@
-/* $Id: s_buffers.c,v 1.11 2002/06/15 02:38:17 brianp Exp $ */
+/* $Id: s_buffers.c,v 1.12 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -167,22 +167,18 @@ clear_color_buffers(GLcontext *ctx)
 
    /* loop over four possible dest color buffers */
    for (bufferBit = 1; bufferBit <= 8; bufferBit = bufferBit << 1) {
-      if (bufferBit & ctx->Color.DrawDestMask) {
+      if (bufferBit & ctx->Color._DrawDestMask) {
          if (bufferBit == FRONT_LEFT_BIT) {
-            (*ctx->Driver.SetDrawBuffer)( ctx, GL_FRONT_LEFT);
-            (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer, GL_FRONT_LEFT);
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_FRONT_LEFT);
          }
          else if (bufferBit == FRONT_RIGHT_BIT) {
-            (*ctx->Driver.SetDrawBuffer)( ctx, GL_FRONT_RIGHT);
-            (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer, GL_FRONT_RIGHT);
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_FRONT_RIGHT);
          }
          else if (bufferBit == BACK_LEFT_BIT) {
-            (*ctx->Driver.SetDrawBuffer)( ctx, GL_BACK_LEFT);
-            (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer, GL_BACK_LEFT);
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_BACK_LEFT);
          }
          else {
-            (*ctx->Driver.SetDrawBuffer)( ctx, GL_BACK_RIGHT);
-            (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer, GL_BACK_RIGHT);
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_BACK_RIGHT);
          }
 
          if (colorMask != 0xffffffff) {
@@ -194,9 +190,8 @@ clear_color_buffers(GLcontext *ctx)
       }
    }
 
-   /* restore default read/draw buffers */
-   (void) (*ctx->Driver.SetDrawBuffer)( ctx, ctx->Color.DriverDrawBuffer );
-   (void) (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer, ctx->Pixel.DriverReadBuffer );
+   /* restore default read/draw buffer */
+   _swrast_use_draw_buffer(ctx);
 }
 
 
@@ -224,7 +219,7 @@ _swrast_Clear( GLcontext *ctx, GLbitfield mask,
 
    /* do software clearing here */
    if (mask) {
-      if (mask & ctx->Color.DrawDestMask)   clear_color_buffers(ctx);
+      if (mask & ctx->Color._DrawDestMask)   clear_color_buffers(ctx);
       if (mask & GL_DEPTH_BUFFER_BIT)    _mesa_clear_depth_buffer(ctx);
       if (mask & GL_ACCUM_BUFFER_BIT)    _mesa_clear_accum_buffer(ctx);
       if (mask & GL_STENCIL_BUFFER_BIT)  _mesa_clear_stencil_buffer(ctx);
@@ -258,3 +253,68 @@ _swrast_alloc_buffers( GLframebuffer *buffer )
       _mesa_alloc_alpha_buffers( buffer );
    }
 }
+
+
+/*
+ * Fallback for ctx->Driver.DrawBuffer()
+ */
+void
+_swrast_DrawBuffer( GLcontext *ctx, GLenum mode )
+{
+   _swrast_use_draw_buffer(ctx);
+}
+
+
+/*
+ * Setup things so that we read/write spans from the user-designated
+ * read buffer (set via glReadPixels).  We usually just have to call
+ * this for glReadPixels, glCopyPixels, etc.
+ */
+void
+_swrast_use_read_buffer( GLcontext *ctx )
+{
+   SWcontext *swrast = SWRAST_CONTEXT(ctx);
+
+   /* Do this so the software-emulated alpha plane span functions work! */
+   ctx->Color._DriverDrawBuffer = ctx->Pixel._DriverReadBuffer;
+   /* Tell the device driver where to read/write spans */
+   (*swrast->Driver.SetBuffer)( ctx, ctx->ReadBuffer,
+                                ctx->Pixel._DriverReadBuffer );
+}
+
+
+/*
+ * Setup things so that we read/write spans from the default draw buffer.
+ * This is the usual mode that Mesa's software rasterizer operates in.
+ */
+void
+_swrast_use_draw_buffer( GLcontext *ctx )
+{
+   SWcontext *swrast = SWRAST_CONTEXT(ctx);
+
+   /* The user can specify rendering to zero, one, two, or four color
+    * buffers simultaneously with glDrawBuffer()!
+    * We don't expect the span/point/line/triangle functions to deal with
+    * that mess so we'll iterate over the multiple buffers as needed.
+    * But usually we only render to one color buffer at a time.
+    * We set ctx->Color._DriverDrawBuffer to that buffer and tell the
+    * device driver to use that buffer.
+    * Look in s_span.c's multi_write_rgba_span() function to see how
+    * we loop over multiple color buffers when needed.
+    */
+
+   if (ctx->Color._DrawDestMask & FRONT_LEFT_BIT)
+      ctx->Color._DriverDrawBuffer = GL_FRONT_LEFT;
+   else if (ctx->Color._DrawDestMask & BACK_LEFT_BIT)
+      ctx->Color._DriverDrawBuffer = GL_BACK_LEFT;
+   else if (ctx->Color._DrawDestMask & FRONT_RIGHT_BIT)
+      ctx->Color._DriverDrawBuffer = GL_FRONT_RIGHT;
+   else if (ctx->Color._DrawDestMask & BACK_RIGHT_BIT)
+      ctx->Color._DriverDrawBuffer = GL_BACK_RIGHT;
+   else
+      /* glDrawBuffer(GL_NONE) */
+      ctx->Color._DriverDrawBuffer = GL_FRONT_LEFT; /* always have this */
+
+   (*swrast->Driver.SetBuffer)( ctx, ctx->DrawBuffer,
+                                ctx->Color._DriverDrawBuffer );
+}
diff --git a/src/mesa/swrast/s_context.c b/src/mesa/swrast/s_context.c
index a4f59df8ae3..105b562d90f 100644
--- a/src/mesa/swrast/s_context.c
+++ b/src/mesa/swrast/s_context.c
@@ -1,4 +1,4 @@
-/* $Id: s_context.c,v 1.35 2002/06/15 03:03:11 brianp Exp $ */
+/* $Id: s_context.c,v 1.36 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -87,8 +87,11 @@ _swrast_update_rasterflags( GLcontext *ctx )
     * MULTI_DRAW_BIT flag.  Also set it if we're drawing to no
     * buffers or the RGBA or CI mask disables all writes.
     */
-   if (ctx->Color.DrawBuffer == GL_FRONT_AND_BACK ||
-       ctx->Color.DrawBuffer == GL_NONE) {
+   if (ctx->Color._DrawDestMask != FRONT_LEFT_BIT &&
+       ctx->Color._DrawDestMask != BACK_LEFT_BIT &&
+       ctx->Color._DrawDestMask != FRONT_RIGHT_BIT &&
+       ctx->Color._DrawDestMask != BACK_RIGHT_BIT) {
+      /* more than one color buffer designated for writing (or zero buffers) */
       RasterMask |= MULTI_DRAW_BIT;
    }
    else if (ctx->Visual.rgbMode && *((GLuint *) ctx->Color.ColorMask) == 0) {
diff --git a/src/mesa/swrast/s_copypix.c b/src/mesa/swrast/s_copypix.c
index 2c6bd263123..7f5f41b78f6 100644
--- a/src/mesa/swrast/s_copypix.c
+++ b/src/mesa/swrast/s_copypix.c
@@ -1,4 +1,4 @@
-/* $Id: s_copypix.c,v 1.38 2002/06/15 03:03:11 brianp Exp $ */
+/* $Id: s_copypix.c,v 1.39 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -103,7 +103,6 @@ copy_conv_rgba_pixels(GLcontext *ctx, GLint srcx, GLint srcy,
    GLboolean quick_draw;
    GLint row;
    GLboolean changeBuffer;
-   GLchan *saveReadAlpha;
    const GLboolean zoom = ctx->Pixel.ZoomX != 1.0F || ctx->Pixel.ZoomY != 1.0F;
    const GLuint transferOps = ctx->_ImageTransferState;
    GLfloat *dest, *tmpImage, *convImage;
@@ -128,7 +127,6 @@ copy_conv_rgba_pixels(GLcontext *ctx, GLint srcx, GLint srcy,
    }
 
    /* If read and draw buffer are different we must do buffer switching */
-   saveReadAlpha = ctx->ReadBuffer->Alpha;
    changeBuffer = ctx->Pixel.ReadBuffer != ctx->Color.DrawBuffer
                || ctx->DrawBuffer != ctx->ReadBuffer;
 
@@ -149,16 +147,8 @@ copy_conv_rgba_pixels(GLcontext *ctx, GLint srcx, GLint srcy,
    dest = tmpImage;
 
    if (changeBuffer) {
-      (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-                                    ctx->Pixel.DriverReadBuffer );
-      if (ctx->Pixel.DriverReadBuffer == GL_FRONT_LEFT)
-         ctx->ReadBuffer->Alpha = ctx->ReadBuffer->FrontLeftAlpha;
-      else if (ctx->Pixel.DriverReadBuffer == GL_BACK_LEFT)
-         ctx->ReadBuffer->Alpha = ctx->ReadBuffer->BackLeftAlpha;
-      else if (ctx->Pixel.DriverReadBuffer == GL_FRONT_RIGHT)
-         ctx->ReadBuffer->Alpha = ctx->ReadBuffer->FrontRightAlpha;
-      else
-         ctx->ReadBuffer->Alpha = ctx->ReadBuffer->BackRightAlpha;
+      /* choose the read buffer */
+      _swrast_use_read_buffer(ctx);
    }
 
    /* read source image */
@@ -176,11 +166,9 @@ copy_conv_rgba_pixels(GLcontext *ctx, GLint srcx, GLint srcy,
       }
    }
 
-   /* read from the draw buffer again (in case of blending) */
    if (changeBuffer) {
-      (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer,
-                                    ctx->Color.DriverDrawBuffer );
-      ctx->ReadBuffer->Alpha = saveReadAlpha;
+      /* restore default src/dst buffer */
+      _swrast_use_draw_buffer(ctx);
    }
 
    /* do image transfer ops up until convolution */
@@ -301,7 +289,6 @@ copy_rgba_pixels(GLcontext *ctx, GLint srcx, GLint srcy,
    GLboolean quick_draw;
    GLint sy, dy, stepy, j;
    GLboolean changeBuffer;
-   GLchan *saveReadAlpha;
    const GLboolean zoom = ctx->Pixel.ZoomX != 1.0F || ctx->Pixel.ZoomY != 1.0F;
    GLint overlapping;
    const GLuint transferOps = ctx->_ImageTransferState;
@@ -347,13 +334,9 @@ copy_rgba_pixels(GLcontext *ctx, GLint srcx, GLint srcy,
    }
 
    /* If read and draw buffer are different we must do buffer switching */
-   saveReadAlpha = ctx->ReadBuffer->Alpha;
    changeBuffer = ctx->Pixel.ReadBuffer != ctx->Color.DrawBuffer
                   || ctx->DrawBuffer != ctx->ReadBuffer;
 
-   (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-                                 ctx->Pixel.DriverReadBuffer );
-
    if (overlapping) {
       GLint ssy = sy;
       tmpImage = (GLchan *) MALLOC(width * height * sizeof(GLchan) * 4);
@@ -361,25 +344,22 @@ copy_rgba_pixels(GLcontext *ctx, GLint srcx, GLint srcy,
          _mesa_error( ctx, GL_OUT_OF_MEMORY, "glCopyPixels" );
          return;
       }
+      /* setup source */
+      if (changeBuffer)
+         _swrast_use_read_buffer(ctx);
+      /* read the source image */
       p = tmpImage;
-      if (changeBuffer) {
-         (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-                                       ctx->Pixel.DriverReadBuffer );
-         if (ctx->Pixel.DriverReadBuffer == GL_FRONT_LEFT)
-            ctx->ReadBuffer->Alpha = ctx->ReadBuffer->FrontLeftAlpha;
-         else if (ctx->Pixel.DriverReadBuffer == GL_BACK_LEFT)
-            ctx->ReadBuffer->Alpha = ctx->ReadBuffer->BackLeftAlpha;
-         else if (ctx->Pixel.DriverReadBuffer == GL_FRONT_RIGHT)
-            ctx->ReadBuffer->Alpha = ctx->ReadBuffer->FrontRightAlpha;
-         else
-            ctx->ReadBuffer->Alpha = ctx->ReadBuffer->BackRightAlpha;
-      }
       for (j = 0; j < height; j++, ssy += stepy) {
          _mesa_read_rgba_span( ctx, ctx->ReadBuffer, width, srcx, ssy,
                             (GLchan (*)[4]) p );
          p += width * 4;
       }
       p = tmpImage;
+      /* restore dest */
+      if (changeBuffer) {
+         _swrast_use_draw_buffer(ctx);
+         changeBuffer = GL_FALSE;
+      }
    }
    else {
       tmpImage = NULL;  /* silence compiler warnings */
@@ -395,30 +375,12 @@ copy_rgba_pixels(GLcontext *ctx, GLint srcx, GLint srcy,
       }
       else {
          /* get from framebuffer */
-         if (changeBuffer) {
-            (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-                                          ctx->Pixel.DriverReadBuffer );
-            if (ctx->Pixel.DriverReadBuffer == GL_FRONT_LEFT) {
-               ctx->ReadBuffer->Alpha = ctx->ReadBuffer->FrontLeftAlpha;
-            }
-            else if (ctx->Pixel.DriverReadBuffer == GL_BACK_LEFT) {
-               ctx->ReadBuffer->Alpha = ctx->ReadBuffer->BackLeftAlpha;
-            }
-            else if (ctx->Pixel.DriverReadBuffer == GL_FRONT_RIGHT) {
-               ctx->ReadBuffer->Alpha = ctx->ReadBuffer->FrontRightAlpha;
-            }
-            else {
-               ctx->ReadBuffer->Alpha = ctx->ReadBuffer->BackRightAlpha;
-            }
-         }
-         _mesa_read_rgba_span( ctx, ctx->ReadBuffer, width, srcx, sy, span->color.rgba );
-      }
-
-      if (changeBuffer) {
-         /* read from the draw buffer again (in case of blending) */
-         (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer,
-                                       ctx->Color.DriverDrawBuffer );
-         ctx->ReadBuffer->Alpha = saveReadAlpha;
+         if (changeBuffer)
+            _swrast_use_read_buffer(ctx);
+         _mesa_read_rgba_span( ctx, ctx->ReadBuffer, width, srcx, sy,
+                               span->color.rgba );
+         if (changeBuffer)
+            _swrast_use_draw_buffer(ctx);
       }
 
       if (transferOps) {
@@ -525,10 +487,6 @@ copy_rgba_pixels(GLcontext *ctx, GLint srcx, GLint srcy,
       }
    }
 
-   /* Restore pixel source to be the draw buffer (for blending, etc) */
-   (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer,
-                                 ctx->Color.DriverDrawBuffer );
-
    if (overlapping)
       FREE(tmpImage);
 }
@@ -576,9 +534,6 @@ static void copy_ci_pixels( GLcontext *ctx,
    changeBuffer = ctx->Pixel.ReadBuffer != ctx->Color.DrawBuffer
                || ctx->DrawBuffer != ctx->ReadBuffer;
 
-   (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-                                 ctx->Pixel.DriverReadBuffer );
-
    if (overlapping) {
       GLint ssy = sy;
       tmpImage = (GLuint *) MALLOC(width * height * sizeof(GLuint));
@@ -586,16 +541,21 @@ static void copy_ci_pixels( GLcontext *ctx,
          _mesa_error( ctx, GL_OUT_OF_MEMORY, "glCopyPixels" );
          return;
       }
+      /* setup source */
+      if (changeBuffer)
+         _swrast_use_read_buffer(ctx);
+      /* read the image */
       p = tmpImage;
-      if (changeBuffer) {
-         (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-                                       ctx->Pixel.DriverReadBuffer );
-      }
       for (j = 0; j < height; j++, ssy += stepy) {
          _mesa_read_index_span( ctx, ctx->ReadBuffer, width, srcx, ssy, p );
          p += width;
       }
       p = tmpImage;
+      /* restore to draw buffer */
+      if (changeBuffer) {
+         _swrast_use_draw_buffer(ctx);
+         changeBuffer = GL_FALSE;
+      }
    }
    else {
       tmpImage = NULL;  /* silence compiler warning */
@@ -608,18 +568,12 @@ static void copy_ci_pixels( GLcontext *ctx,
          p += width;
       }
       else {
-         if (changeBuffer) {
-            (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-                                          ctx->Pixel.DriverReadBuffer );
-         }
+         if (changeBuffer)
+            _swrast_use_read_buffer(ctx);
          _mesa_read_index_span( ctx, ctx->ReadBuffer, width, srcx, sy,
                                 span->color.index );
-      }
-
-      if (changeBuffer) {
-         /* set read buffer back to draw buffer (in case of logicops) */
-         (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer,
-                                       ctx->Color.DriverDrawBuffer );
+         if (changeBuffer)
+            _swrast_use_draw_buffer(ctx);
       }
 
       if (shift_or_offset) {
@@ -638,10 +592,6 @@ static void copy_ci_pixels( GLcontext *ctx,
          _mesa_write_index_span(ctx, span);
    }
 
-   /* Restore pixel source to be the draw buffer (for blending, etc) */
-   (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer,
-                                 ctx->Color.DriverDrawBuffer );
-
    if (overlapping)
       FREE(tmpImage);
 }
diff --git a/src/mesa/swrast/s_imaging.c b/src/mesa/swrast/s_imaging.c
index 1c63f5c3416..98cbe347a72 100644
--- a/src/mesa/swrast/s_imaging.c
+++ b/src/mesa/swrast/s_imaging.c
@@ -1,4 +1,4 @@
-/* $Id: s_imaging.c,v 1.5 2002/04/04 16:53:00 brianp Exp $ */
+/* $Id: s_imaging.c,v 1.6 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -37,12 +37,10 @@ _swrast_CopyColorTable( GLcontext *ctx,
 			GLenum target, GLenum internalformat,
 			GLint x, GLint y, GLsizei width)
 {
-   SWcontext *swrast = SWRAST_CONTEXT(ctx);
    GLchan data[MAX_WIDTH][4];
 
    /* Select buffer to read from */
-   (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-                                 ctx->Pixel.DriverReadBuffer );
+   _swrast_use_read_buffer(ctx);
 
    if (width > MAX_WIDTH)
       width = MAX_WIDTH;
@@ -51,8 +49,7 @@ _swrast_CopyColorTable( GLcontext *ctx,
    _mesa_read_rgba_span( ctx, ctx->ReadBuffer, width, x, y, data );
 
    /* Restore reading from draw buffer (the default) */
-   (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer,
-                                 ctx->Color.DriverDrawBuffer );
+   _swrast_use_draw_buffer(ctx);
 
    glColorTable(target, internalformat, width, GL_RGBA, CHAN_TYPE, data);
 }
@@ -61,12 +58,10 @@ void
 _swrast_CopyColorSubTable( GLcontext *ctx,GLenum target, GLsizei start,
 			   GLint x, GLint y, GLsizei width)
 {
-   SWcontext *swrast = SWRAST_CONTEXT(ctx);
    GLchan data[MAX_WIDTH][4];
 
    /* Select buffer to read from */
-   (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-                                 ctx->Pixel.DriverReadBuffer );
+   _swrast_use_read_buffer(ctx);
 
    if (width > MAX_WIDTH)
       width = MAX_WIDTH;
@@ -75,8 +70,7 @@ _swrast_CopyColorSubTable( GLcontext *ctx,GLenum target, GLsizei start,
    _mesa_read_rgba_span( ctx, ctx->ReadBuffer, width, x, y, data );
 
    /* Restore reading from draw buffer (the default) */
-   (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer,
-                                 ctx->Color.DriverDrawBuffer );
+   _swrast_use_draw_buffer(ctx);
 
    glColorSubTable(target, start, width, GL_RGBA, CHAN_TYPE, data);
 }
@@ -90,6 +84,9 @@ _swrast_CopyConvolutionFilter1D(GLcontext *ctx, GLenum target,
    SWcontext *swrast = SWRAST_CONTEXT(ctx);
    GLchan rgba[MAX_CONVOLUTION_WIDTH][4];
 
+   /* Select buffer to read from */
+   _swrast_use_read_buffer(ctx);
+
    RENDER_START( swrast, ctx );
 
    /* read the data from framebuffer */
@@ -98,6 +95,9 @@ _swrast_CopyConvolutionFilter1D(GLcontext *ctx, GLenum target,
    
    RENDER_FINISH( swrast, ctx );
 
+   /* Restore reading from draw buffer (the default) */
+   _swrast_use_draw_buffer(ctx);
+
    /* store as convolution filter */
    glConvolutionFilter1D(target, internalFormat, width,
 			 GL_RGBA, CHAN_TYPE, rgba);
@@ -114,6 +114,9 @@ _swrast_CopyConvolutionFilter2D(GLcontext *ctx, GLenum target,
    GLchan rgba[MAX_CONVOLUTION_HEIGHT][MAX_CONVOLUTION_WIDTH][4];
    GLint i;
 
+   /* Select buffer to read from */
+   _swrast_use_read_buffer(ctx);
+
    RENDER_START(swrast,ctx);
    
    /* read pixels from framebuffer */
@@ -124,6 +127,9 @@ _swrast_CopyConvolutionFilter2D(GLcontext *ctx, GLenum target,
 
    RENDER_FINISH(swrast,ctx);
 
+   /* Restore reading from draw buffer (the default) */
+   _swrast_use_draw_buffer(ctx);
+
    /*
     * HACK: save & restore context state so we can store this as a
     * convolution filter via the GL api.  Doesn't call any callbacks
diff --git a/src/mesa/swrast/s_readpix.c b/src/mesa/swrast/s_readpix.c
index a52cd8e7c0b..f925e791162 100644
--- a/src/mesa/swrast/s_readpix.c
+++ b/src/mesa/swrast/s_readpix.c
@@ -1,4 +1,4 @@
-/* $Id: s_readpix.c,v 1.14 2002/04/19 00:38:27 brianp Exp $ */
+/* $Id: s_readpix.c,v 1.15 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -62,9 +62,7 @@ read_index_pixels( GLcontext *ctx,
       return;
    }
 
-   ASSERT(swrast->Driver.SetReadBuffer);
-   (*swrast->Driver.SetReadBuffer)(ctx, ctx->ReadBuffer,
-                                ctx->Pixel.DriverReadBuffer);
+   _swrast_use_read_buffer(ctx);
 
    readWidth = (width > MAX_WIDTH) ? MAX_WIDTH : width;
 
@@ -82,8 +80,7 @@ read_index_pixels( GLcontext *ctx,
                             &ctx->Pack, ctx->_ImageTransferState);
    }
 
-   (*swrast->Driver.SetReadBuffer)(ctx, ctx->DrawBuffer,
-                                ctx->Color.DriverDrawBuffer);
+   _swrast_use_draw_buffer(ctx);
 }
 
 
@@ -318,13 +315,13 @@ read_rgba_pixels( GLcontext *ctx,
    SWcontext *swrast = SWRAST_CONTEXT(ctx);
    GLint readWidth;
 
-   (*swrast->Driver.SetReadBuffer)(ctx, ctx->ReadBuffer, ctx->Pixel.DriverReadBuffer);
+   _swrast_use_read_buffer(ctx);
 
    /* Try optimized path first */
    if (read_fast_rgba_pixels( ctx, x, y, width, height,
                               format, type, pixels, packing )) {
 
-      (*swrast->Driver.SetReadBuffer)(ctx, ctx->DrawBuffer, ctx->Color.DriverDrawBuffer);
+      _swrast_use_draw_buffer(ctx);
       return; /* done! */
    }
 
@@ -470,7 +467,7 @@ read_rgba_pixels( GLcontext *ctx,
       }
    }
 
-   (*swrast->Driver.SetReadBuffer)(ctx, ctx->DrawBuffer, ctx->Color.DriverDrawBuffer);
+   _swrast_use_draw_buffer(ctx);
 }
 
 
diff --git a/src/mesa/swrast/s_span.c b/src/mesa/swrast/s_span.c
index a3271d7806d..94cd4a9ce83 100644
--- a/src/mesa/swrast/s_span.c
+++ b/src/mesa/swrast/s_span.c
@@ -1,4 +1,4 @@
-/* $Id: s_span.c,v 1.44 2002/06/15 03:03:11 brianp Exp $ */
+/* $Id: s_span.c,v 1.45 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -608,19 +608,19 @@ multi_write_index_span( GLcontext *ctx, struct sw_span *span )
    GLuint bufferBit;
 
    /* loop over four possible dest color buffers */
-   for (bufferBit = 1; bufferBit <= 8; bufferBit = bufferBit << 1) {
-      if (bufferBit & ctx->Color.DrawDestMask) {
+   for (bufferBit = 1; bufferBit <= 8; bufferBit <<= 1) {
+      if (bufferBit & ctx->Color._DrawDestMask) {
          GLuint indexTmp[MAX_WIDTH];
          ASSERT(span->end < MAX_WIDTH);
 
          if (bufferBit == FRONT_LEFT_BIT)
-            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_FRONT_LEFT);
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_FRONT_LEFT);
          else if (bufferBit == FRONT_RIGHT_BIT)
-            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_FRONT_RIGHT);
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_FRONT_RIGHT);
          else if (bufferBit == BACK_LEFT_BIT)
-            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_BACK_LEFT);
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_BACK_LEFT);
          else
-            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_BACK_RIGHT);
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_BACK_RIGHT);
 
          /* make copy of incoming indexes */
          MEMCPY( indexTmp, span->color.index, span->end * sizeof(GLuint) );
@@ -648,7 +648,7 @@ multi_write_index_span( GLcontext *ctx, struct sw_span *span )
    }
 
    /* restore default dest buffer */
-   (void) (*ctx->Driver.SetDrawBuffer)( ctx, ctx->Color.DriverDrawBuffer);
+   _swrast_use_draw_buffer(ctx);
 }
 
 
@@ -670,26 +670,26 @@ multi_write_rgba_span( GLcontext *ctx, struct sw_span *span )
       return;
 
    /* loop over four possible dest color buffers */
-   for (bufferBit = 1; bufferBit <= 8; bufferBit = bufferBit << 1) {
-      if (bufferBit & ctx->Color.DrawDestMask) {
+   for (bufferBit = 1; bufferBit <= 8; bufferBit <<= 1) {
+      if (bufferBit & ctx->Color._DrawDestMask) {
          GLchan rgbaTmp[MAX_WIDTH][4];
          ASSERT(span->end < MAX_WIDTH);
 
          if (bufferBit == FRONT_LEFT_BIT) {
-            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_FRONT_LEFT);
-            ctx->DrawBuffer->Alpha = ctx->DrawBuffer->FrontLeftAlpha;
+            ctx->Color._DriverDrawBuffer = GL_FRONT_LEFT;
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_FRONT_LEFT);
          }
          else if (bufferBit == FRONT_RIGHT_BIT) {
-            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_FRONT_RIGHT);
-            ctx->DrawBuffer->Alpha = ctx->DrawBuffer->FrontRightAlpha;
+            ctx->Color._DriverDrawBuffer = GL_FRONT_RIGHT;
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_FRONT_RIGHT);
          }
          else if (bufferBit == BACK_LEFT_BIT) {
-            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_BACK_LEFT);
-            ctx->DrawBuffer->Alpha = ctx->DrawBuffer->BackLeftAlpha;
+            ctx->Color._DriverDrawBuffer = GL_BACK_LEFT;
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_BACK_LEFT);
          }
          else {
-            (void) (*ctx->Driver.SetDrawBuffer)( ctx, GL_BACK_RIGHT);
-            ctx->DrawBuffer->Alpha = ctx->DrawBuffer->BackRightAlpha;
+            ctx->Color._DriverDrawBuffer = GL_BACK_RIGHT;
+            (*swrast->Driver.SetBuffer)(ctx, ctx->DrawBuffer, GL_BACK_RIGHT);
          }
 
          /* make copy of incoming colors */
@@ -734,7 +734,7 @@ multi_write_rgba_span( GLcontext *ctx, struct sw_span *span )
    }
 
    /* restore default dest buffer */
-   (void) (*ctx->Driver.SetDrawBuffer)( ctx, ctx->Color.DriverDrawBuffer );
+   _swrast_use_draw_buffer(ctx);
 }
 
 
diff --git a/src/mesa/swrast/s_texstore.c b/src/mesa/swrast/s_texstore.c
index e1adeded7fc..88fe786ef8c 100644
--- a/src/mesa/swrast/s_texstore.c
+++ b/src/mesa/swrast/s_texstore.c
@@ -1,4 +1,4 @@
-/* $Id: s_texstore.c,v 1.5 2001/05/21 16:41:04 brianp Exp $ */
+/* $Id: s_texstore.c,v 1.6 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -73,8 +73,7 @@ read_color_image( GLcontext *ctx, GLint x, GLint y,
       return NULL;
 
    /* Select buffer to read from */
-   (*swrast->Driver.SetReadBuffer)( ctx, ctx->ReadBuffer,
-                                 ctx->Pixel.DriverReadBuffer );
+   _swrast_use_read_buffer(ctx);
 
    RENDER_START(swrast,ctx);
 
@@ -89,8 +88,7 @@ read_color_image( GLcontext *ctx, GLint x, GLint y,
    RENDER_FINISH(swrast,ctx);
 
    /* Read from draw buffer (the default) */
-   (*swrast->Driver.SetReadBuffer)( ctx, ctx->DrawBuffer,
-                                 ctx->Color.DriverDrawBuffer );
+   _swrast_use_draw_buffer(ctx);
 
    return image;
 }
diff --git a/src/mesa/swrast/s_triangle.c b/src/mesa/swrast/s_triangle.c
index bdbdde76b83..634664371bd 100644
--- a/src/mesa/swrast/s_triangle.c
+++ b/src/mesa/swrast/s_triangle.c
@@ -1,4 +1,4 @@
-/* $Id: s_triangle.c,v 1.59 2002/06/15 03:03:12 brianp Exp $ */
+/* $Id: s_triangle.c,v 1.60 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -218,7 +218,7 @@ static void simple_textured_triangle( GLcontext *ctx,
       span->intTex[1] += span->intTexStep[1];				\
    }									\
    (*swrast->Driver.WriteRGBSpan)(ctx, span->end, span->x, span->y,	\
-                                  (CONST GLchan (*)[3]) span->color.rgb,	\
+                                  (CONST GLchan (*)[3]) span->color.rgb,\
                                   NULL );
 
 #include "s_tritemp.h"
@@ -283,7 +283,7 @@ static void simple_z_textured_triangle( GLcontext *ctx,
       span->z += span->zStep;						\
    }									\
    (*swrast->Driver.WriteRGBSpan)(ctx, span->end, span->x, span->y,	\
-                                  (CONST GLchan (*)[3]) span->color.rgb,	\
+                                  (CONST GLchan (*)[3]) span->color.rgb,\
                                   span->mask );
 
 #include "s_tritemp.h"
@@ -589,7 +589,7 @@ static void affine_textured_triangle( GLcontext *ctx,
    info.format = obj->Image[b]->Format;					\
    info.filter = obj->MinFilter;					\
    info.envmode = unit->EnvMode;					\
-   span->arrayMask |= SPAN_RGBA;						\
+   span->arrayMask |= SPAN_RGBA;					\
 									\
    if (info.envmode == GL_BLEND) {					\
       /* potential off-by-one error here? (1.0f -> 2048 -> 0) */	\
@@ -896,7 +896,7 @@ static void persp_textured_triangle( GLcontext *ctx,
 
 #define RENDER_SPAN( span )			\
    span->interpMask &= ~SPAN_RGBA;		\
-   span->arrayMask |= SPAN_RGBA;			\
+   span->arrayMask |= SPAN_RGBA;		\
    fast_persp_span(ctx, span, &info);
 
 #include "s_tritemp.h"
@@ -976,7 +976,7 @@ static void occlusion_zless_triangle( GLcontext *ctx,
 #define RENDER_SPAN( span )				\
    GLuint i;						\
    for (i = 0; i < span->end; i++) {			\
-      GLdepth z = FixedToDepth(span->z);			\
+      GLdepth z = FixedToDepth(span->z);		\
       if (z < zRow[i]) {				\
          ctx->OcclusionResult = GL_TRUE;		\
          return;					\
diff --git a/src/mesa/swrast/swrast.h b/src/mesa/swrast/swrast.h
index f36031cfb4a..a33e97ec017 100644
--- a/src/mesa/swrast/swrast.h
+++ b/src/mesa/swrast/swrast.h
@@ -1,4 +1,4 @@
-/* $Id: swrast.h,v 1.24 2002/04/19 14:05:50 brianp Exp $ */
+/* $Id: swrast.h,v 1.25 2002/07/09 01:22:52 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
@@ -204,6 +204,12 @@ struct swrast_device_driver;
 extern void
 _swrast_alloc_buffers( GLframebuffer *buffer );
 
+extern void
+_swrast_use_read_buffer( GLcontext *ctx );
+
+extern void
+_swrast_use_draw_buffer( GLcontext *ctx );
+
 extern GLboolean
 _swrast_CreateContext( GLcontext *ctx );
 
@@ -254,6 +260,10 @@ _swrast_Accum( GLcontext *ctx, GLenum op,
 	       GLint width, GLint height );
 
 
+extern void
+_swrast_DrawBuffer( GLcontext *ctx, GLenum mode );
+
+
 /* Reset the stipple counter
  */
 extern void
@@ -363,11 +373,14 @@ _swrast_copy_texsubimage3d(GLcontext *ctx,
  */
 struct swrast_device_driver {
 
-   void (*SetReadBuffer)( GLcontext *ctx, GLframebuffer *colorBuffer,
-                          GLenum buffer );
+   void (*SetBuffer)( GLcontext *ctx, GLframebuffer *buffer,
+                      GLenum colorBuffer );
    /*
-    * Specifies the current buffer for span/pixel reading.
-    * colorBuffer will be one of:
+    * Specifies the current buffer for span/pixel writing/reading.
+    * buffer indicates which window to write to / read from.  Normally,
+    * this'll be the buffer currently bound to the context, but it doesn't
+    * have to be!
+    * colorBuffer indicates which color buffer, one of:
     *    GL_FRONT_LEFT - this buffer always exists
     *    GL_BACK_LEFT - when double buffering
     *    GL_FRONT_RIGHT - when using stereo