XS prototype (or not) problem?

BrowserUk has asked for the wisdom of the Perl Monks concerning the following question:

Update: My bad. I was including an alpha value in the color array. Being used to perl sub just ignoring extra args whilst I worked out how to use aplha values in OpenGL. But XS subs aren't like perl subs, and the extra value causes the sub to print it's usage message and fail. :(

I finally got OpenGL built and installed and I'm just starting to play with it and I encountered a Perl problem that I haven't experienced before. I'm trying to call glColor3f() within a subroutine into which I'm passing an array ref containing the rgb values.

My first attempt was: glColor3f( @$ref ); fails!
But that (and all other failures) bellyaches Usage: OpenGL::glColor3f(red, green, blue) at...
So then I tried hard coding the numbers:glColor3f( 1.0, 0.0, 0.0 ); works!
So then I tried glColor3f( $ref->[ 0 ], $ref->[ 1 ], $ref->[ 2 ] ); works!
Hm! Prototype problem? &glColor3f( @$ref ); Fails!
Then I tried: glColor3f( @{ $ref }[ 0, 1, 2 ] ); works!
Then I tried: glColor3f( map $_, @$ref ); fails!

Quick peruse of the xs source shows:

void
glColor3f(red, green, blue)
    GLfloat red
    GLfloat green
    GLfloat blue
[download]

Which doesn't clarify what's going on. Can you?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

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Re: XS prototype (or not) problem? by salva (Canon) on Jul 24, 2008 at 08:47 UTC
what does `prototype` say about the function? `use OpenGL; print prototype("OpenGL::glColor3f"), "\n";` [download] When the module is compiled, a OpenGL.c file is generated, can you post the code for the function wrapper? Also, how is the function registered in the interpreter? Look for a `cv = newXS("OpenGL::glColor3f", ...)` statement probably followed by `sv_setpv((SV*)cv, "$$$")` to set the prototype	[reply] [d/l] [select]
Re: XS prototype (or not) problem? by syphilis (Archbishop) on Jul 24, 2008 at 08:13 UTC
`glColor3f( @$ref );` fails! Can't reproduce the problem: `C:\_32\comp\OpenGL>perl -MOpenGL -e "@x=1.0,0.0,0.0);$ref=\@x,OpenGL:: +glColor3f(@$ref)" C:\_32\comp\OpenGL>` [download] Which version of OpenGL ? (I have the upcoming 0.57 built from svn source - so it may be that an old problem has been fixed.) Cheers, Rob	[reply] [d/l] [select]
Re^2: XS prototype (or not) problem? (Solved) by BrowserUk (Patriarch) on Jul 24, 2008 at 08:30 UTC
I don't get an error if I do that either, but (I think) that's because nothing has been initialised yet. Try this: #! perl -slw use strict; use OpenGL qw[ :all ]; print "Version: ", $OpenGL::VERSION; glutInit(); glutInitDisplayMode( GLUT_RGBA \| GLUT_DOUBLE \| GLUT_DEPTH \| GLUT_ALPHA + ); glutInitWindowSize( 1024, 768 ); my $main = glutCreateWindow( 'OGL1' ); glutDisplayFunc( \&render ); glutMainLoop(); sub render { glClearColor( 1, 1, 1, 1 ); glClear(GL_COLOR_BUFFER_BIT); drawPolygon( #### One too many arguments!!! (I'd added an alpha value) [ 1.0, 0.0, 0.0, 0.0 ], # red [ 0.25, 0.25, 0.25 ], [ 0.75, 0.25, 0.25 ], [ 0.75, 0.75, 0.25 ], [ 0.25, 0.75, 0.25 ], ); glutSwapBuffers(); } sub drawPolygon { glBegin(GL_POLYGON); ## glColor3f( @{ shift() }[ 0, 1, 2 ] ); ## Works glColor3f( @{ shift() } ); ## Fails glVertex3f( @$_ ) for @_; glEnd(); } [download] Switch the comment card in drawPloygon to see it work. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l]
Re^3: XS prototype (or not) problem? (Solved) by syphilis (Archbishop) on Jul 24, 2008 at 09:21 UTC
`sub drawPolygon { glBegin(GL_POLYGON); ## glColor3f( @{ shift() }[ 0, 1, 2 ] ); ## Works glColor3f( @{ shift() } ); ## Fails glVertex3f( @$_ ) for @_; glEnd(); }` [download] In the call that works glColor3f() receives 3 arguments. In the call that fails glColor3f() receives 4 arguments - which rightly warrants a "Usage" error. The following rendition of sub drawPolygon works fine for me: `sub drawPolygon { glBegin(GL_POLYGON); my $arg = shift; pop(@$arg); ## glColor3f( @{ shift() }[ 0, 1, 2 ] ); ## Works glColor3f( @{ $arg } ); glVertex3f( @$_ ) for @_; glEnd(); }` [download] Update: Duh, you'd already worked it out for yourself. I missed the "Solved" and didn't pay attention to the comments. Cheers, Rob	[reply] [d/l] [select]
Re: XS prototype (or not) problem? by cdarke (Prior) on Jul 24, 2008 at 07:59 UTC
When you say "Fails!", how does it fail? What is the error message? You suspect a prototype issue, in the XS is there a PROTOTYPE statement?	[reply]
Re^2: XS prototype (or not) problem? by Anonymous Monk on Jul 24, 2008 at 08:08 UTC
Maybe recompile with `#define GL_GLEXT_PROTOTYPES 0`	[reply] [d/l]
Re^2: XS prototype (or not) problem? by BrowserUk (Patriarch) on Jul 24, 2008 at 08:08 UTC
I do give the error message in my post. And if there was a PROTOTYPE statement in the .xs file, I would have posted it. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]