That's a pretty good idea. I tried to make the Pointer class as simple
(and stupid) as possible but we might need some convenience APIs on
top of it, for those not familiar with the Objective-C encoding types.
Here is an API proposal based on Brian's snippet... thoughts?
class Pointer
def self.new(type='@')
new_with_type(type)
end
TYPES = {
:int => 'i',
:uint => 'I',
...
}
def self.to(sym)
new_with_type(TYPES[sym])
end
def value
self[0]
end
end
# I'm pretty sure I already wrote something similar in RubyCocoa.
Laurent
On Feb 25, 2009, at 1:16 PM, Matt Aimonetti wrote:
Thanks Brian for the detailed explanation. I wonder if your Pointer
extension shouldn't be merged into HotCocoa or MacRuby itself.
What do you guys think?
- Matt
On Wed, Feb 25, 2009 at 12:43 PM, Brian Chapados <[email protected]>
wrote:
Can you explain: "^{_CGLRendererInfoObject=}"? is that some secret
incantation only known by the MacRuby/Obj overlords?
Yes, it is actually a 7th level spell: 'Encode Structure'. To learn
it, you must study the ancient tome:
http://developer.apple.com/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/chapter_7_section_1.html#/
/apple_ref/doc/uid/TP40008048-CH100-SW1
If it makes you feel better, I usually need to look it up (or just
run the Obj-C code sample), unless it is something simple (like '@').
I don't keep this spell in memory, as it is only required in special
situations.
Seriously though, that is actually how you encode a pointer to a
struct. If you use the @encode(type) directive, the compiler will
return the runtime encoding for 'type'. It's a bit cryptic, but not
too bad once you know the syntax:
'^type' encodes a pointer to type.
'{name=<field1 type><field2 type><field3 type>...<fieldN type>}'
encodes a struct with N fields.
To break it down using 2 examples:
(from the docs)
typedef struct example {
id anObject; // encoding = @
char *aString; // encoding = c
int anInt; // enoding = i
} Example;
@encode(Example) = "^{examp...@ci}"
CGLRendererInfoObj is a pointer to an opaque struct (we don't know
anything about the fields) named _CGLRendererInfoObject. All we know
is:
typedef struct _CGLRendererInfoObject *CGLRendererInfoObj;
so it's just "^{_CGLRendererInfoObject=}"
In practice (unless you're working with CoreFoundation C APIs) you
usually just need a pointer to an object. The most common usage I
run
across is to retrieve NSError objects. The CoreFoundation C API uses
pass-by-reference extensively. To use these functions with MacRuby,
you need to create lots of pointer objects. In general, this is an
area where interfacing ruby with C is just fugly. I'd personally
avoid doing this in MacRuby. If you find yourself needing to use
lots
Pointer objects, it's probably better and less error-prone to write
that code in C and expose it to MacRuby through an Objective-C
interface.
That said, for common things, I've used something like this extension
to the Pointer class:
----
class Pointer
def self.ptr
new_with_type("@")
end
def self.to(type = :object)
case type
when :object
new_with_type('@')
when :int
new_with_type('i')
when :char
when :bool
when :BOOL
new_with_type('c')
when :unsigned
new_with_type('I')
end
end
def value
self[0]
end
end
----
Need a pointer to an ObjC object?
p = Pointer.ptr
To a BOOL?
p = Pointer.to(:BOOL)
Need the value?
p.value
Those are the most common types I've needed.
On Wed, Feb 25, 2009 at 11:11 AM, Matt Aimonetti
<[email protected]> wrote:
Brian, what's up with this syntax: info =
Pointer.new_with_type("^{_CGLRendererInfoObject=}")
Can you explain: "^{_CGLRendererInfoObject=}"? is that some secret
incantation only known by the MacRuby/Obj overlords?
Thanks,
- Matt
On Wed, Feb 25, 2009 at 10:13 AM, Brian Chapados
<[email protected]> wrote:
CGLRendererInfo is a pointer to a struct:
typedef struct _CGLRendererInfoObject *CGLRendererInfoObj;
try creating a pointer to void or to the struct:
info = Pointer.new_with_type("^v") # void *info;
or
info = Pointer.new_with_type("^{_CGLRendererInfoObject=}") #
CGLRendererInfo *info
I think the second one is effectively the same as what you were
trying
to do with:
info = Pointer.new_with_type("CGLRendererInfoObj")
except that the runtime doesn't know what to do with
"CGLRendererInfo". The argument to Pointer.new_with_type must be a
valid Objective-C type encoding[1].
[1]:
http://developer.apple.com/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/chapter_7_section_1.html#/
/apple_ref/doc/uid/TP40008048-CH100-SW1
If you are ever in doubt about what encoding to use, you can always
compile a small Objective-C program that prints out the output of
@encode(). For example:
#import <Foundation/Foundation.h>
#import <OpenGL/OpenGL.h>
int main(int argc, char *argv[])
{
char *encoding = @encode(CGLRendererInfoObj);
printf("\nencoding => %s\n\n", encoding);
return 0;
}
compile with:
gcc -Wall -o encode encode.m -framework Foundation -framework
OpenGL
then run:
./encode
Maybe there is an easier way to obtain the output of @encode().
I'm not
sure.
Brian
On Wed, Feb 25, 2009 at 1:42 AM, Julien Jassaud <[email protected]
>
wrote:
Hello,
I am trying to port the Cocoa OpenGL sample to MacRuby and
encountered a
few
problems.
First, I can't access some constants defined in an enum in
GLTypes.h. Do
I
need to port those constants to ruby by hand ? Is that related
to gen_bridge_metadata ?
Second, I need to use CGLQueryRendererInfo
and CGLDescribeRenderer functions. The first one requires a
pointer to
a CGLRendererInfoObj structure but the second requires the
object to be
passed directly. I tried some C style pointer arithmetic :
info = Pointer.new_with_type("CGLRendererInfoObj")
count = Pointer.new_with_type("l")
CGLQueryRendererInfo(caps[:cgl_display_mask], info, count) <-
works
fine,
but CGLRendererInfoObj is opaque so I can't check it in irb.
CGLDescribeRenderer(info[0], 0, kCGLRPRendererCount, count) <- I
naively
tried to dereference the pointer, but it doesn't work.
CGLDescribeRenderer(info, 0, kCGLRPRendererCount, count) <- No
complaints,
but the value for count[0] is not consistent (100468704
renderers).
I see in MacIRB that there is a CGLRendererInfoObj class but I
can't instantiate it.
This is all new to me and I may be overlooking something
obvious. If
anyone
has an idea, please help.
Thanks,
Julien Jassaud
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