implementation of _swrast_BlitFramebuffer()

1 files changed, 754 insertions, 4 deletions

diff --git a/src/mesa/swrast/s_blit.c b/src/mesa/swrast/s_blit.c
index 0d08a4effc..5aec4aad03 100644
--- a/src/mesa/swrast/s_blit.c
+++ b/src/mesa/swrast/s_blit.c
@@ -28,13 +28,763 @@
 #include "s_context.h"
 
 
+#define ABS(X)   ((X) < 0 ? -(X) : (X))
+
+
+/**
+ * Generate a row resampler function for GL_NEAREST mode.
+ */
+#define RESAMPLE(NAME, PIXELTYPE, SIZE)			\
+static void						\
+NAME(GLint srcWidth, GLint dstWidth,			\
+     const GLvoid *srcBuffer, GLvoid *dstBuffer,	\
+     GLboolean flip)					\
+{							\
+   const PIXELTYPE *src = (const PIXELTYPE *) srcBuffer;\
+   PIXELTYPE *dst = (PIXELTYPE *) dstBuffer;		\
+   GLint dstCol;					\
+							\
+   if (flip) {						\
+      for (dstCol = 0; dstCol < dstWidth; dstCol++) {	\
+         GLint srcCol = (dstCol * srcWidth) / dstWidth;	\
+         ASSERT(srcCol >= 0);				\
+         ASSERT(srcCol < srcWidth);			\
+         srcCol = srcWidth - 1 - srcCol; /* flip */	\
+         if (SIZE == 1) {				\
+            dst[dstCol] = src[srcCol];			\
+         }						\
+         else if (SIZE == 2) {				\
+            dst[dstCol*2+0] = src[srcCol*2+0];		\
+            dst[dstCol*2+1] = src[srcCol*2+1];		\
+         }						\
+         else if (SIZE == 4) {				\
+            dst[dstCol*4+0] = src[srcCol*4+0];		\
+            dst[dstCol*4+1] = src[srcCol*4+1];		\
+            dst[dstCol*4+2] = src[srcCol*4+2];		\
+            dst[dstCol*4+3] = src[srcCol*4+3];		\
+         }						\
+      }							\
+   }							\
+   else {						\
+      for (dstCol = 0; dstCol < dstWidth; dstCol++) {	\
+         GLint srcCol = (dstCol * srcWidth) / dstWidth;	\
+         ASSERT(srcCol >= 0);				\
+         ASSERT(srcCol < srcWidth);			\
+         if (SIZE == 1) {				\
+            dst[dstCol] = src[srcCol];			\
+         }						\
+         else if (SIZE == 2) {				\
+            dst[dstCol*2+0] = src[srcCol*2+0];		\
+            dst[dstCol*2+1] = src[srcCol*2+1];		\
+         }						\
+         else if (SIZE == 4) {				\
+            dst[dstCol*4+0] = src[srcCol*4+0];		\
+            dst[dstCol*4+1] = src[srcCol*4+1];		\
+            dst[dstCol*4+2] = src[srcCol*4+2];		\
+            dst[dstCol*4+3] = src[srcCol*4+3];		\
+         }						\
+      }							\
+   }							\
+}
+
+/**
+ * Resamplers for 1, 2, 4, 8 and 16-byte pixels.
+ */
+RESAMPLE(resample_row_1, GLubyte, 1)
+RESAMPLE(resample_row_2, GLushort, 1)
+RESAMPLE(resample_row_4, GLuint, 1)
+RESAMPLE(resample_row_8, GLuint, 2)
+RESAMPLE(resample_row_16, GLuint, 4)
+
+
+/**
+ * Blit color, depth or stencil with GL_NEAREST filtering.
+ */
+static void
+blit_nearest(GLcontext *ctx,
+             GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
+             GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1,
+             GLenum buffer)
+{
+   struct gl_renderbuffer *readRb, *drawRb;
+
+   const GLint srcWidth = ABS(srcX1 - srcX0);
+   const GLint dstWidth = ABS(dstX1 - dstX0);
+   const GLint srcHeight = ABS(srcY1 - srcY0);
+   const GLint dstHeight = ABS(dstY1 - dstY0);
+
+   const GLint srcXpos = MIN2(srcX0, srcX1);
+   const GLint srcYpos = MIN2(srcY0, srcY1);
+   const GLint dstXpos = MIN2(dstX0, dstX1);
+   const GLint dstYpos = MIN2(dstY0, dstY1);
+
+   const GLboolean invertX = (srcX1 < srcX0) ^ (dstX1 < dstX0);
+   const GLboolean invertY = (srcY1 < srcY0) ^ (dstY1 < dstY0);
+
+   GLint dstRow;
+
+   GLint comps, pixelSize;
+   GLvoid *srcBuffer, *dstBuffer;
+   GLint prevY = -1;
+
+   typedef void (*resample_func)(GLint srcWidth, GLint dstWidth,
+                                 const GLvoid *srcBuffer, GLvoid *dstBuffer,
+                                 GLboolean flip);
+   resample_func resampleRow;
+
+   switch (buffer) {
+   case GL_COLOR_BUFFER_BIT:
+      readRb = ctx->ReadBuffer->_ColorReadBuffer;
+      drawRb = ctx->DrawBuffer->_ColorDrawBuffers[0][0];
+      comps = 4;
+      break;
+   case GL_DEPTH_BUFFER_BIT:
+      readRb = ctx->ReadBuffer->_DepthBuffer;
+      drawRb = ctx->DrawBuffer->_DepthBuffer;
+      comps = 1;
+      break;
+   case GL_STENCIL_BUFFER_BIT:
+      readRb = ctx->ReadBuffer->_StencilBuffer;
+      drawRb = ctx->DrawBuffer->_StencilBuffer;
+      comps = 1;
+      break;
+   default:
+      _mesa_problem(ctx, "unexpected buffer in blit_nearest()");
+      return;
+   }
+
+   switch (readRb->DataType) {
+   case GL_UNSIGNED_BYTE:
+      pixelSize = comps * sizeof(GLubyte);
+      break;
+   case GL_UNSIGNED_SHORT:
+      pixelSize = comps * sizeof(GLushort);
+      break;
+   case GL_UNSIGNED_INT:
+      pixelSize = comps * sizeof(GLuint);
+      break;
+   case GL_FLOAT:
+      pixelSize = comps * sizeof(GLfloat);
+      break;
+   default:
+      _mesa_problem(ctx, "unexpected buffer type (0x%x) in blit_nearest",
+                    readRb->DataType);
+      return;
+   }
+
+   /* choose row resampler */
+   switch (pixelSize) {
+   case 1:
+      resampleRow = resample_row_1;
+      break;
+   case 2:
+      resampleRow = resample_row_2;
+      break;
+   case 4:
+      resampleRow = resample_row_4;
+      break;
+   case 8:
+      resampleRow = resample_row_8;
+      break;
+   case 16:
+      resampleRow = resample_row_16;
+      break;
+   default:
+      _mesa_problem(ctx, "unexpected pixel size (%d) in blit_nearest",
+                    pixelSize);
+      return;
+   }
+
+   /* allocate the src/dst row buffers */
+   srcBuffer = _mesa_malloc(pixelSize * srcWidth);
+   if (!srcBuffer) {
+      _mesa_error(ctx, GL_OUT_OF_MEMORY, "glBlitFrameBufferEXT");
+      return;
+   }
+   dstBuffer = _mesa_malloc(pixelSize * dstWidth);
+   if (!dstBuffer) {
+      _mesa_free(srcBuffer);
+      _mesa_error(ctx, GL_OUT_OF_MEMORY, "glBlitFrameBufferEXT");
+      return;
+   }
+
+   for (dstRow = 0; dstRow < dstHeight; dstRow++) {
+      const GLint dstY = dstYpos + dstRow;
+      GLint srcRow = (dstRow * srcHeight) / dstHeight;
+      GLint srcY;
+
+      ASSERT(srcRow >= 0);
+      ASSERT(srcRow < srcHeight);
+
+      if (invertY) {
+         srcRow = srcHeight - 1 - srcRow;
+      }
+
+      srcY = srcYpos + srcRow;
+
+      /* get pixel row from source and resample to match dest width */
+      if (prevY != srcY) {
+         readRb->GetRow(ctx, readRb, srcWidth, srcXpos, srcY, srcBuffer);
+         (*resampleRow)(srcWidth, dstWidth, srcBuffer, dstBuffer, invertX);
+         prevY = srcY;
+      }
+
+      /* store pixel row in destination */
+      drawRb->PutRow(ctx, drawRb, dstWidth, dstXpos, dstY, dstBuffer, NULL);
+   }
+
+   _mesa_free(srcBuffer);
+   _mesa_free(dstBuffer);
+}
+
+
+
+#define LERP(T, A, B)  ( (A) + (T) * ((B) - (A)) )
+
+static INLINE GLfloat
+lerp_2d(GLfloat a, GLfloat b,
+        GLfloat v00, GLfloat v10, GLfloat v01, GLfloat v11)
+{
+   const GLfloat temp0 = LERP(a, v00, v10);
+   const GLfloat temp1 = LERP(a, v01, v11);
+   return LERP(b, temp0, temp1);
+}
+
+
+/**
+ * Bilinear interpolation of two source rows.
+ * GLubyte pixels.
+ */
+static void
+resample_linear_row_ub(GLint srcWidth, GLint dstWidth,
+                       const GLvoid *srcBuffer0, const GLvoid *srcBuffer1,
+                       GLvoid *dstBuffer, GLboolean flip, GLfloat rowWeight)
+{
+   const GLubyte (*srcColor0)[4] = (const GLubyte (*)[4]) srcBuffer0;
+   const GLubyte (*srcColor1)[4] = (const GLubyte (*)[4]) srcBuffer1;
+   GLubyte (*dstColor)[4] = (GLubyte (*)[4]) dstBuffer;
+   const GLfloat dstWidthF = (GLfloat) dstWidth;
+   GLint dstCol;
+
+   for (dstCol = 0; dstCol < dstWidth; dstCol++) {
+      const GLfloat srcCol = (dstCol * srcWidth) / dstWidthF;
+      GLint srcCol0 = IFLOOR(srcCol);
+      GLint srcCol1 = srcCol0 + 1;
+      GLfloat colWeight = srcCol - srcCol0; /* fractional part of srcCol */
+      GLfloat red, green, blue, alpha;
+
+      ASSERT(srcCol0 >= 0);
+      ASSERT(srcCol0 < srcWidth);
+      ASSERT(srcCol1 <= srcWidth);
+
+      if (srcCol1 == srcWidth) {
+         /* last column fudge */
+         srcCol1--;
+         colWeight = 0.0;
+      }
+
+      if (flip) {
+         srcCol0 = srcWidth - 1 - srcCol0;
+         srcCol1 = srcWidth - 1 - srcCol1;
+      }
+
+      red = lerp_2d(colWeight, rowWeight,
+                    srcColor0[srcCol0][RCOMP], srcColor0[srcCol1][RCOMP],
+                    srcColor1[srcCol0][RCOMP], srcColor1[srcCol1][RCOMP]);
+      green = lerp_2d(colWeight, rowWeight,
+                    srcColor0[srcCol0][GCOMP], srcColor0[srcCol1][GCOMP],
+                    srcColor1[srcCol0][GCOMP], srcColor1[srcCol1][GCOMP]);
+      blue = lerp_2d(colWeight, rowWeight,
+                    srcColor0[srcCol0][BCOMP], srcColor0[srcCol1][BCOMP],
+                    srcColor1[srcCol0][BCOMP], srcColor1[srcCol1][BCOMP]);
+      alpha = lerp_2d(colWeight, rowWeight,
+                    srcColor0[srcCol0][ACOMP], srcColor0[srcCol1][ACOMP],
+                    srcColor1[srcCol0][ACOMP], srcColor1[srcCol1][ACOMP]);
+      
+      dstColor[dstCol][RCOMP] = IFLOOR(red);
+      dstColor[dstCol][GCOMP] = IFLOOR(green);
+      dstColor[dstCol][BCOMP] = IFLOOR(blue);
+      dstColor[dstCol][ACOMP] = IFLOOR(alpha);
+   }
+}
+
+
+
+/**
+ * Bilinear filtered blit (color only).
+ */
+static void
+blit_linear(GLcontext *ctx,
+            GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
+            GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1)
+{
+   struct gl_renderbuffer *readRb = ctx->ReadBuffer->_ColorReadBuffer;
+   struct gl_renderbuffer *drawRb = ctx->DrawBuffer->_ColorDrawBuffers[0][0];
+
+   const GLint srcWidth = ABS(srcX1 - srcX0);
+   const GLint dstWidth = ABS(dstX1 - dstX0);
+   const GLint srcHeight = ABS(srcY1 - srcY0);
+   const GLint dstHeight = ABS(dstY1 - dstY0);
+   const GLfloat dstHeightF = (GLfloat) dstHeight;
+
+   const GLint srcXpos = MIN2(srcX0, srcX1);
+   const GLint srcYpos = MIN2(srcY0, srcY1);
+   const GLint dstXpos = MIN2(dstX0, dstX1);
+   const GLint dstYpos = MIN2(dstY0, dstY1);
+
+   const GLboolean invertX = (srcX1 < srcX0) ^ (dstX1 < dstX0);
+   const GLboolean invertY = (srcY1 < srcY0) ^ (dstY1 < dstY0);
+
+   GLint dstRow;
+
+   GLint pixelSize;
+   GLvoid *srcBuffer0, *srcBuffer1;
+   GLint srcBufferY0 = -1, srcBufferY1 = -1;
+   GLvoid *dstBuffer;
+
+   switch (readRb->DataType) {
+   case GL_UNSIGNED_BYTE:
+      pixelSize = 4 * sizeof(GLubyte);
+      break;
+   case GL_UNSIGNED_SHORT:
+      pixelSize = 4 * sizeof(GLushort);
+      break;
+   case GL_UNSIGNED_INT:
+      pixelSize = 4 * sizeof(GLuint);
+      break;
+   case GL_FLOAT:
+      pixelSize = 4 * sizeof(GLfloat);
+      break;
+   default:
+      _mesa_problem(ctx, "unexpected buffer type (0x%x) in blit_nearest",
+                    readRb->DataType);
+      return;
+   }
+
+   /* Allocate the src/dst row buffers.
+    * Keep two adjacent src rows around for bilinear sampling.
+    */
+   srcBuffer0 = _mesa_malloc(pixelSize * srcWidth);
+   if (!srcBuffer0) {
+      _mesa_error(ctx, GL_OUT_OF_MEMORY, "glBlitFrameBufferEXT");
+      return;
+   }
+   srcBuffer1 = _mesa_malloc(pixelSize * srcWidth);
+   if (!srcBuffer1) {
+      _mesa_free(srcBuffer0);
+      _mesa_error(ctx, GL_OUT_OF_MEMORY, "glBlitFrameBufferEXT");
+      return;
+   }
+   dstBuffer = _mesa_malloc(pixelSize * dstWidth);
+   if (!dstBuffer) {
+      _mesa_free(srcBuffer0);
+      _mesa_free(srcBuffer1);
+      _mesa_error(ctx, GL_OUT_OF_MEMORY, "glBlitFrameBufferEXT");
+      return;
+   }
+
+   for (dstRow = 0; dstRow < dstHeight; dstRow++) {
+      const GLint dstY = dstYpos + dstRow;
+      const GLfloat srcRow = (dstRow * srcHeight) / dstHeightF;
+      GLint srcRow0 = IFLOOR(srcRow);
+      GLint srcRow1 = srcRow0 + 1;
+      GLfloat rowWeight = srcRow - srcRow0; /* fractional part of srcRow */
+
+      ASSERT(srcRow >= 0);
+      ASSERT(srcRow < srcHeight);
+
+      if (srcRow1 == srcHeight) {
+         /* last row fudge */
+         srcRow1 = srcRow0;
+         rowWeight = 0.0;
+      }
+
+      if (invertY) {
+         srcRow0 = srcHeight - 1 - srcRow0;
+         srcRow1 = srcHeight - 1 - srcRow1;
+      }
+
+      srcY0 = srcYpos + srcRow0;
+      srcY1 = srcYpos + srcRow1;
+
+      /* get the two source rows */
+      if (srcY0 == srcBufferY0 && srcY1 == srcBufferY1) {
+         /* use same source row buffers again */
+      }
+      else if (srcY0 == srcBufferY1) {
+         /* move buffer1 into buffer0 by swapping pointers */
+         GLvoid *tmp = srcBuffer0;
+         srcBuffer0 = srcBuffer1;
+         srcBuffer1 = tmp;
+         /* get y1 row */
+         readRb->GetRow(ctx, readRb, srcWidth, srcXpos, srcY1, srcBuffer1);
+         srcBufferY0 = srcY0;
+         srcBufferY1 = srcY1;
+      }
+      else {
+         /* get both new rows */
+         readRb->GetRow(ctx, readRb, srcWidth, srcXpos, srcY0, srcBuffer0);
+         readRb->GetRow(ctx, readRb, srcWidth, srcXpos, srcY1, srcBuffer1);
+         srcBufferY0 = srcY0;
+         srcBufferY1 = srcY1;
+      }
+
+      if (readRb->DataType == GL_UNSIGNED_BYTE) {
+         resample_linear_row_ub(srcWidth, dstWidth, srcBuffer0, srcBuffer1,
+                                dstBuffer, invertX, rowWeight);
+      }
+      else {
+         _mesa_problem(ctx, "Unsupported color channel type in sw blit");
+         break;
+      }
+
+      /* store pixel row in destination */
+      drawRb->PutRow(ctx, drawRb, dstWidth, dstXpos, dstY, dstBuffer, NULL);
+   }
+
+   _mesa_free(srcBuffer0);
+   _mesa_free(srcBuffer1);
+   _mesa_free(dstBuffer);
+}
+
+
+/**
+ * Simple case:  Blit color, depth or stencil with no scaling or flipping.
+ * XXX we could easily support vertical flipping here.
+ */
+static void
+simple_blit(GLcontext *ctx,
+            GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
+            GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1,
+            GLenum buffer)
+{
+   struct gl_renderbuffer *readRb, *drawRb;
+   const GLint width = srcX1 - srcX0;
+   const GLint height = srcY1 - srcY0;
+   GLint row, srcY, dstY, yStep;
+   GLint comps, bytesPerRow;
+   void *rowBuffer;
+
+   /* only one buffer */
+   ASSERT(_mesa_bitcount(buffer) == 1);
+   /* no flipping checks */
+   ASSERT(srcX0 < srcX1);
+   ASSERT(srcY0 < srcY1);
+   ASSERT(dstX0 < dstX1);
+   ASSERT(dstY0 < dstY1);
+   /* size checks */
+   ASSERT(srcX1 - srcX0 == dstX1 - dstX0);
+   ASSERT(srcY1 - srcY0 == dstY1 - dstY0);
+
+   /* determine if copy should be bottom-to-top or top-to-bottom */
+   if (srcY0 > dstY0) {
+      /* src above dst: copy bottom-to-top */
+      yStep = 1;
+      srcY = srcY0;
+      dstY = dstY0;
+   }
+   else {
+      /* src below dst: copy top-to-bottom */
+      yStep = -1;
+      srcY = srcY1 - 1;
+      dstY = dstY1 - 1;
+   }
+
+   switch (buffer) {
+   case GL_COLOR_BUFFER_BIT:
+      readRb = ctx->ReadBuffer->_ColorReadBuffer;
+      drawRb = ctx->DrawBuffer->_ColorDrawBuffers[0][0];
+      comps = 4;
+      break;
+   case GL_DEPTH_BUFFER_BIT:
+      readRb = ctx->ReadBuffer->_DepthBuffer;
+      drawRb = ctx->DrawBuffer->_DepthBuffer;
+      comps = 1;
+      break;
+   case GL_STENCIL_BUFFER_BIT:
+      readRb = ctx->ReadBuffer->_StencilBuffer;
+      drawRb = ctx->DrawBuffer->_StencilBuffer;
+      comps = 1;
+      break;
+   default:
+      _mesa_problem(ctx, "unexpected buffer in simple_blit()");
+      return;
+   }
+
+   ASSERT(readRb->DataType == drawRb->DataType);
+
+   /* compute bytes per row */
+   switch (readRb->DataType) {
+   case GL_UNSIGNED_BYTE:
+      bytesPerRow = comps * width * sizeof(GLubyte);
+      break;
+   case GL_UNSIGNED_SHORT:
+      bytesPerRow = comps * width * sizeof(GLushort);
+      break;
+   case GL_UNSIGNED_INT:
+      bytesPerRow = comps * width * sizeof(GLuint);
+      break;
+   case GL_FLOAT:
+      bytesPerRow = comps * width * sizeof(GLfloat);
+      break;
+   default:
+      _mesa_problem(ctx, "unexpected buffer type in simple_blit");
+      return;
+   }
+
+   /* allocate the row buffer */
+   rowBuffer = _mesa_malloc(bytesPerRow);
+   if (!rowBuffer) {
+      _mesa_error(ctx, GL_OUT_OF_MEMORY, "glBlitFrameBufferEXT");
+      return;
+   }
+
+   for (row = 0; row < height; row++) {
+      readRb->GetRow(ctx, readRb, width, srcX0, srcY, rowBuffer);
+      drawRb->PutRow(ctx, drawRb, width, dstX0, dstY, rowBuffer, NULL);
+      srcY += yStep;
+      dstY += yStep;
+   }
+
+   _mesa_free(rowBuffer);
+}
+
+
+/**
+ * Clip dst coords against Xmax (or Ymax).
+ */
+static INLINE void
+clip_right_or_top(GLint *srcX0, GLint *srcX1,
+                  GLint *dstX0, GLint *dstX1,
+                  GLint maxValue)
+{
+   GLfloat t, bias;
+
+   if (*dstX1 > maxValue) {
+      /* X1 outside right edge */
+      ASSERT(*dstX0 < maxValue); /* X0 should be inside right edge */
+      t = (GLfloat) (maxValue - *dstX0) / (GLfloat) (*dstX1 - *dstX0);
+      /* chop off [t, 1] part */
+      ASSERT(t >= 0.0 && t <= 1.0);
+      *dstX1 = maxValue;
+      bias = (*srcX0 < *srcX1) ? 0.5 : -0.5;
+      *srcX1 = *srcX0 + (GLint) (t * (*srcX1 - *srcX0) + bias);
+   }
+   else if (*dstX0 > maxValue) {
+      /* X0 outside right edge */
+      ASSERT(*dstX1 < maxValue); /* X1 should be inside right edge */
+      t = (GLfloat) (maxValue - *dstX1) / (GLfloat) (*dstX0 - *dstX1);
+      /* chop off [t, 1] part */
+      ASSERT(t >= 0.0 && t <= 1.0);
+      *dstX0 = maxValue;
+      bias = (*srcX0 < *srcX1) ? -0.5 : 0.5;
+      *srcX0 = *srcX1 + (GLint) (t * (*srcX0 - *srcX1) + bias);
+   }
+}
+
+
+/**
+ * Clip dst coords against Xmin (or Ymin).
+ */
+static INLINE void
+clip_left_or_bottom(GLint *srcX0, GLint *srcX1,
+                    GLint *dstX0, GLint *dstX1,
+                    GLint minValue)
+{
+   GLfloat t, bias;
+
+   if (*dstX0 < minValue) {
+      /* X0 outside left edge */
+      ASSERT(*dstX1 > minValue); /* X1 should be inside left edge */
+      t = (GLfloat) (minValue - *dstX0) / (GLfloat) (*dstX1 - *dstX0);
+      /* chop off [0, t] part */
+      ASSERT(t >= 0.0 && t <= 1.0);
+      *dstX0 = minValue;
+      bias = (*srcX0 < *srcX1) ? 0.5 : -0.5; /* flipped??? */
+      *srcX0 = *srcX0 + (GLint) (t * (*srcX1 - *srcX0) + bias);
+   }
+   else if (*dstX1 < minValue) {
+      /* X1 outside left edge */
+      ASSERT(*dstX0 > minValue); /* X0 should be inside left edge */
+      t = (GLfloat) (minValue - *dstX1) / (GLfloat) (*dstX0 - *dstX1);
+      /* chop off [0, t] part */
+      ASSERT(t >= 0.0 && t <= 1.0);
+      *dstX1 = minValue;
+      bias = (*srcX0 < *srcX1) ? 0.5 : -0.5;
+      *srcX1 = *srcX1 + (GLint) (t * (*srcX0 - *srcX1) + bias);
+   }
+}
+
+
+/**
+ * Do clipping of blit src/dest rectangles.
+ * The dest rect is clipped against both the buffer bounds and scissor bounds.
+ * The src rect is just clipped against the buffer bounds.
+ *
+ * When either the src or dest rect is clipped, the other is also clipped
+ * proportionately!
+ *
+ * Note that X0 need not be less than X1 (same for Y) for either the source
+ * and dest rects.  That makes the clipping a little trickier.
+ *
+ * \return GL_TRUE if anything is left to draw, GL_FALSE if totally clipped
+ */
+static GLboolean
+clip_blit(GLcontext *ctx,
+          GLint *srcX0, GLint *srcY0, GLint *srcX1, GLint *srcY1,
+          GLint *dstX0, GLint *dstY0, GLint *dstX1, GLint *dstY1)
+{
+   const GLint srcXmin = 0;
+   const GLint srcXmax = ctx->ReadBuffer->Width;
+   const GLint srcYmin = 0;
+   const GLint srcYmax = ctx->ReadBuffer->Height;
+
+   /* these include scissor bounds */
+   const GLint dstXmin = ctx->DrawBuffer->_Xmin;
+   const GLint dstXmax = ctx->DrawBuffer->_Xmax;
+   const GLint dstYmin = ctx->DrawBuffer->_Ymin;
+   const GLint dstYmax = ctx->DrawBuffer->_Ymax;
+
+   /*
+   printf("PreClipX:  src: %d .. %d  dst: %d .. %d\n",
+          *srcX0, *srcX1, *dstX0, *dstX1);
+   printf("PreClipY:  src: %d .. %d  dst: %d .. %d\n",
+          *srcY0, *srcY1, *dstY0, *dstY1);
+   */
+
+   /* trivial rejection tests */
+   if (*dstX0 == *dstX1)
+      return GL_FALSE; /* no width */
+   if (*dstX0 <= dstXmin && *dstX1 <= dstXmin)
+      return GL_FALSE; /* totally out (left) of bounds */
+   if (*dstX0 >= dstXmax && *dstX1 >= dstXmax)
+      return GL_FALSE; /* totally out (right) of bounds */
+
+   if (*dstY0 == *dstY1)
+      return GL_FALSE;
+   if (*dstY0 <= dstYmin && *dstY1 <= dstYmin)
+      return GL_FALSE;
+   if (*dstY0 >= dstYmax && *dstY1 >= dstYmax)
+      return GL_FALSE;
+
+   if (*srcX0 == *srcX1)
+      return GL_FALSE;
+   if (*srcX0 <= srcXmin && *srcX1 <= srcXmin)
+      return GL_FALSE;
+   if (*srcX0 >= srcXmax && *srcX1 >= srcXmax)
+      return GL_FALSE;
+
+   if (*srcY0 == *srcY1)
+      return GL_FALSE;
+   if (*srcY0 <= srcYmin && *srcY1 <= srcYmin)
+      return GL_FALSE;
+   if (*srcY0 >= srcYmax && *srcY1 >= srcYmax)
+      return GL_FALSE;
+
+   /*
+    * dest clip
+    */
+   clip_right_or_top(srcX0, srcX1, dstX0, dstX1, dstXmax);
+   clip_right_or_top(srcY0, srcY1, dstY0, dstY1, dstYmax);
+   clip_left_or_bottom(srcX0, srcX1, dstX0, dstX1, dstXmin);
+   clip_left_or_bottom(srcY0, srcY1, dstY0, dstY1, dstYmin);
+
+   /*
+    * src clip (just swap src/dst values from above)
+    */
+   clip_right_or_top(dstX0, dstX1, srcX0, srcX1, srcXmax);
+   clip_right_or_top(dstY0, dstY1, srcY0, srcY1, srcYmax);
+   clip_left_or_bottom(dstX0, dstX1, srcX0, srcX1, srcXmin);
+   clip_left_or_bottom(dstY0, dstY1, srcY0, srcY1, srcYmin);
+
+   /*
+   printf("PostClipX: src: %d .. %d  dst: %d .. %d\n",
+          *srcX0, *srcX1, *dstX0, *dstX1);
+   printf("PostClipY: src: %d .. %d  dst: %d .. %d\n",
+          *srcY0, *srcY1, *dstY0, *dstY1);
+   */
+
+   ASSERT(*dstX0 >= dstXmin);
+   ASSERT(*dstX0 <= dstXmax);
+   ASSERT(*dstX1 >= dstXmin);
+   ASSERT(*dstX1 <= dstXmax);
+
+   ASSERT(*dstY0 >= dstYmin);
+   ASSERT(*dstY0 <= dstYmax);
+   ASSERT(*dstY1 >= dstYmin);
+   ASSERT(*dstY1 <= dstYmax);
+
+   ASSERT(*srcX0 >= srcXmin);
+   ASSERT(*srcX0 <= srcXmax);
+   ASSERT(*srcX1 >= srcXmin);
+   ASSERT(*srcX1 <= srcXmax);
+
+   ASSERT(*srcY0 >= srcYmin);
+   ASSERT(*srcY0 <= srcYmax);
+   ASSERT(*srcY1 >= srcYmin);
+   ASSERT(*srcY1 <= srcYmax);
+
+   return GL_TRUE;
+}
+
+
 /**
  * Software fallback for glBlitFramebufferEXT().
  */
 void
-_swrast_blit_framebuffer(GLcontext *ctx,
-                         GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
-                         GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1,
-                         GLbitfield mask, GLenum filter)
+_swrast_BlitFramebuffer(GLcontext *ctx,
+                        GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
+                        GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1,
+                        GLbitfield mask, GLenum filter)
 {
+   SWcontext *swrast = SWRAST_CONTEXT(ctx);
+   static const GLint buffers[3] = {
+      GL_COLOR_BUFFER_BIT,
+      GL_DEPTH_BUFFER_BIT,
+      GL_STENCIL_BUFFER_BIT
+   };
+   GLint i;
+
+   if (!clip_blit(ctx, &srcX0, &srcY0, &srcX1, &srcY1,
+                  &dstX0, &dstY0, &dstX1, &dstY1)) {
+      return;
+   }
+
+   RENDER_START(swrast, ctx);
+
+   if (srcX1 - srcX0 == dstX1 - dstX0 &&
+       srcY1 - srcY0 == dstY1 - dstY0 &&
+       srcX0 < srcX1 &&
+       srcY0 < srcY1 &&
+       dstX0 < dstX1 &&
+       dstY0 < dstY1) {
+      /* no stretching or flipping.
+       * filter doesn't matter.
+       */
+      for (i = 0; i < 3; i++) {
+         if (mask & buffers[i]) {
+            simple_blit(ctx, srcX0, srcY0, srcX1, srcY1,
+                        dstX0, dstY0, dstX1, dstY1, buffers[i]);
+         }
+      }
+   }
+   else {
+      if (filter == GL_NEAREST) {
+         for (i = 0; i < 3; i++) {
+            if (mask & buffers[i]) {
+               blit_nearest(ctx,  srcX0, srcY0, srcX1, srcY1,
+                            dstX0, dstY0, dstX1, dstY1, buffers[i]);
+            }
+         }
+      }
+      else {
+         ASSERT(filter == GL_LINEAR);
+         if (mask & GL_COLOR_BUFFER_BIT) {  /* depth/stencil not allowed */
+            blit_linear(ctx,  srcX0, srcY0, srcX1, srcY1,
+                        dstX0, dstY0, dstX1, dstY1);
+         }
+      }
+   }
+
+   RENDER_FINISH(swrast, ctx);
 }