Set polygon mode?

[Hugh Perkins]

Hi, question, how do I do "Gl.glPolygonMode(Gl.GL_BACK, Gl.GL_LINE);" in HOpenGl?

Maybe something like "polygonMode $= (Line,Line)" ?

(By the way, what does "$=" do?)


_______________________________________________
HOpenGL mailing list
HOpenGL@...
http://www.haskell.org/mailman/listinfo/hopengl

[Sebastian Sylvan]

On 21/07/07, Hugh Perkins <hughperkins@...> wrote:
> Hi, question, how do I do "Gl.glPolygonMode(Gl.GL_BACK, Gl.GL_LINE);" in
> HOpenGl?
>
> Maybe something like "polygonMode $= (Line,Line)" ?
>
> (By the way, what does "$=" do?)
>

>From the docs (
http://www.haskell.org/ghc/docs/latest/html/libraries/index.html ):

polygonMode :: StateVar (PolygonMode, PolygonMode)

So apparently it's a value of type "StateVar ...". Right, so look up
StateVar and we see that it's a data type wich is an instance of
HasGetter and HasSetter. So it appears that it models some sort of
mutable state variable. In this case we want to set the variable, so
HasSetter seems like the right place to look:

class HasSetter s where
       ($=) :: s a -> a -> IO ()

There's no textual description in the doc, but from the type and name
of the class it looks like this takes a statevar, a value, and sets
the state variable to the value. So indeed the following should do
what you want:

polygonMode $= (Line,Line)

And now you should also know what that operator does. It's just a
convenient way of setting OpenGL state variables (and you can also
find e.g. ($~) which modifies a state variable by the function you
pass it).

--
Sebastian Sylvan
[phone]
UIN: 44640862
_______________________________________________
HOpenGL mailing list
HOpenGL@...
http://www.haskell.org/mailman/listinfo/hopengl

[C Flynn]

On Sun, 22 Jul 2007, Sebastian Sylvan wrote:

> On 21/07/07, Hugh Perkins <hughperkins@...> wrote:
>> Hi, question, how do I do "Gl.glPolygonMode(Gl.GL_BACK, Gl.GL_LINE);" in
>> HOpenGl?
>>
>> Maybe something like "polygonMode $= (Line,Line)" ?
>>
>> (By the way, what does "$=" do?)
>>
>
>> From the docs (
> http://www.haskell.org/ghc/docs/latest/html/libraries/index.html ):
>
> polygonMode :: StateVar (PolygonMode, PolygonMode)
>
> So apparently it's a value of type "StateVar ...". Right, so look up
> StateVar and we see that it's a data type wich is an instance of
> HasGetter and HasSetter. So it appears that it models some sort of
> mutable state variable. In this case we want to set the variable, so
> HasSetter seems like the right place to look:
>
> class HasSetter s where
>      ($=) :: s a -> a -> IO ()
>
> There's no textual description in the doc, but from the type and name
> of the class it looks like this takes a statevar, a value, and sets
> the state variable to the value. So indeed the following should do
> what you want:
>
> polygonMode $= (Line,Line)
>
> And now you should also know what that operator does. It's just a
> convenient way of setting OpenGL state variables (and you can also
> find e.g. ($~) which modifies a state variable by the function you
> pass it).
>

I quite like the $= operator. Makes it clear you're playing around with an
underlying state variable. In the C binding it's often not clear you're
doing this which can lead to unexpected behaviours.

Charles,
_______________________________________________
HOpenGL mailing list
HOpenGL@...
http://www.haskell.org/mailman/listinfo/hopengl