---
name: "OpenGL::Modern::Helpers"
section: "3pm"
platform: "linux"
package: "libopengl-modern-perl"
version: "0.04-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/OpenGL::Modern::Helpers"
---

# OpenGL::Modern::Helpers(3pm)

example usage of raw pointers from perl

## NAME

OpenGL::Modern::Helpers - example usage of raw pointers from perl

## WARNING

This API is an experiment and will change!

## OpenGL::Modern API Implementation

This module exists to support the use of the OpenGL::Modern package for OpenGL bindings by documenting details of the implementation and giving example routines showing the use from perl.

### Implementation

OpenGL::Modern is an XS module providings bindings to the C OpenGL library for graphics.  As such, it needs to handle conversion of input arguments from perl into the required datatypes for the C OpenGL API, it then calls the OpenGL routine, and then converts the return value (if any) from the C API datatype into an appropriate Perl type.

*Scalar Values*

Routines that take scalar values and return scalar values at the C level, are nicely mapped by the built in typemap conversions.  For example:

```
  GLenum
  glCheckNamedFramebufferStatus(GLuint framebuffer, GLenum target);
```

where the functions takes two values, one an integer and one an enumeration which is basically an integer value as well.  The return value is another enumeration/integer value.  Since perl scalars can hold integers, the default XS implementation from perl would be prototyped in perl as

```
  $status = glCheckNamedFramebufferStatus($framebuffer, $target);
```

or, taking advantage of the binding of all the OpenGL enumerations to perl constant functions we could write

```
  $status = glCheckNamedFramebufferStatus($framebuffer, GL_DRAW_FRAMEBUFFER);
```

The key here is explicit scalar values and types which makes the XS perl implementation essentially the same at the C one just with perl scalars in place of C typed values. Of the 2743 OpenGL API routines, 1092 have scalar input and return values and can be considered implemented as is.

*Pointer Values*

The remaining OpenGL routines all have one (or more) pointer argument or return value which are not so simply mapped into perl because the use of pointers from C does not fully determine the use of those values:

- •

  Pointers can be used to return values from routines

- •

  Pointers can be used to pass single input values

- •

  Pointers can be used to pass multiple input values

- •

  Pointers can be used to return multiple input values

The current XS implementation now represents non-char type pointers as the typemap T\_PTR and the string and character pointers are T\_PV.  The routines will be renamed with an added \_c so as to indicate that the mapping is the direct C one.

These \_c routines closely match the OpenGL C API but it requires that the perl user hand manage the allocation, initialization, packing and unpacking, etc for each function call.

Please see this source file for the implementations of

```
  glGetShaderInfoLog_p
  glGetProgramInfoLog_p
  glGetVersion_p
  croak_on_gl_error
```

showing the use of some utility routines to interface to the OpenGL API routines.  OpenGL::Modern::Helpers will be kept up to date with each release to document the API implementations and usage as the bindings evolve and improve.  Once standardized and stable, a final version of Helpers.pm will be released.