Add MapRenderbuffer implementations for software drivers.

Mesa core's is generic for things like osmesa.

For swrast_dri.so, we have to do Y flipping.  The front-buffer path
isn't actually tested, though, because both before and after it fails
with a BadMatch in XGetImage.

Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/main/renderbuffer.c

@@ -1716,6 +1716,33 @@ _mesa_soft_renderbuffer_storage(struct gl_context *ctx, struct gl_renderbuffer *
 }
 
 
+void
+_mesa_map_soft_renderbuffer(struct gl_context *ctx,
+			    struct gl_renderbuffer *rb,
+			    GLuint x, GLuint y, GLuint w, GLuint h,
+			    GLbitfield mode,
+			    GLubyte **out_map,
+			    GLint *out_stride)
+{
+   GLubyte *map = rb->Data;
+   int cpp = _mesa_get_format_bytes(rb->Format);
+   int stride = rb->RowStride * cpp;
+
+   ASSERT(rb->Data);
+
+   map += y * stride;
+   map += x * cpp;
+
+   *out_map = map;
+   *out_stride = stride;
+}
+
+void
+_mesa_unmap_soft_renderbuffer(struct gl_context *ctx,
+			      struct gl_renderbuffer *rb)
+{
+}
+
 
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