OK, if that's the case then it's something I did not know.
I always thought that ALL parameters were passed byval unless
explicitly passed byref. Meaning that changes made to the passed
variable were not reflected in the original object. I now see that
this is true only for base data types (strings, integers, doubles etc).
Is there any harm in explicitly declaring the graphics parameter
byRef??? I like explicitly declared code, I find it easier to keep
track of my variables. I'm really not a fan of the linker "taking
care of stuff" for me unless I explicitly declare it. It's what made
me start this thread in the first place (it was changing the name of
a parameter I passed ByRef from "CanvasName" to the expression
"self.CanvasName", and of course you can't pass expressions as ByRef)
If it is an issue (and please let me know if it is, testing hasn't
proven it one way or the other) I'll just have to break my habit.
It's nice to know there's still stuff I don't know after all these
years though....
- Tom
On 18/02/2007, at 9:30 PM, Andy Dent wrote:
On 18/02/2007, at 6:45 PM, Tom Benson wrote:
There is a factor, though not significant.
The resulting image from all the graphics operation I perform is
huge, in the tens of MB's.
Accessing the graphics of the canvas ByRef enables me to draw
directly to the original object, instead of duplicating the
current content and then passing the resulting graphics object
back to the container.
It doesn't make much of a difference for smaller routines. but
this routine is physically to big to be contained in a single
method, even too big for two, so I have split it up into 34
different block drawing sub routines.
As an aside, passing the graphics object ByRef means that two or
more of these sub routines can operate simultaneously (well, not
simultaneously, but co-operatively) on the graphics object at the
same time. Which is necessary for this app, as for why it's
necessary it's a little difficult to explain...
Tom, maybe I'm not getting something, but what about your
explanation makes you think ByRef enables it as opposed to a normal
object pointer?
Anything other than a primitive data type like an integer IS passed
"by reference" in Pascal terms (or in C terms, as a pointer).
Say you have something like
sub MangleImage(g as Graphics)
When you call MangleImage with MyCanvas.Graphics, the reference
count in MyCanvas.Graphics is updated and MangleImage receives the
same reference to a Graphics object as exists in the MyCanvas
property.
There's no copying of MB's occurring.
In fact, I can't think of a circumstance where passing a Graphics
object ByRef could *ever* make sense - the advantage of using ByRef
means you can create a new object and return it in the parameter
but Graphics objects are always externally supplied by the
framework, not things you should be creating in your code.
regards
Andy
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