Re: Merging the OpenGLRaw and gl packages

[Sven Panne-2]

After some discussions via email and via the Wiki (https://github.com/haskell-opengl/OpenGLRaw/wiki/Merging-OpenGLRaw-and-gl), I've already made a few changes to OpenGLRaw, bringing it closer to 'gl'. These are fully backwards compatible, because they mainly consist of improvements in the generated documentation and the addition of various extension-related retrieval functions. Before I move on and introduce breaking changes, I'd like to hear some opinions about a few items which might need some more discussion:

  * Should OpenGLRaw use pattern synonyms? (Probably yes, but note that this implies GHC >= 7.8.1)

  * Should OpenGLRaw use the 'Half' type from the 'half' package? (Probably yes, but again this implies GHC 7.8.1)

  * Should the incredibly long 'Graphics.Rendering.OpenGL.Raw' module prefix be replaced by the more palatable 'Graphics.GL.Raw'? (Probably yes)

More details and other already resolved and/or less controversial items can be found on the Wiki. The plan is to release a new OpenGLRaw version soon (3.0), after which Edward and Gabríel Arthúr can deprecate the 'gl' package (if they like).

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[Sven Panne-2]

2015-09-30 17:02 GMT+02:00 Casey McCann <[hidden email]>:

On Wed, Sep 30, 2015 at 10:29 AM, Sven Panne <[hidden email]> wrote:
>   * Should OpenGLRaw use pattern synonyms? (Probably yes, but note that this
> implies GHC >= 7.8.1)
>
>   * Should OpenGLRaw use the 'Half' type from the 'half' package? (Probably
> yes, but again this implies GHC 7.8.1)

7.8.1 is, what, a year and a half old?

I'm all for bleeding edge personally but not everyone feels that way,
and that seems pretty severe relative to the benefits.

That's my biggest concern, too, and that's why I wanted to hear other people's opinions: IMHO using pattern synonyms vs. plain old Haskell values is to a large part just bikeshedding, at least in the trivial case at hand where we talk about simple integral values. It basically boils down to the question: Is

   foo x = case x of

     GL_BAR -> expr1

     GL_BAZ -> expr2

     _ -> expr3

really so much better than

   foo x

     | x == GL_BAR = expr1

     | x == GL_BAZ = expr2

     | otherwise = expr3

that we want to drop support for GHC < 7.8.1? Personally, I'm not convinced, but if most other people think that it's OK, I'm willing to pay the price for the sake of merging the packages. Edward claims that using pattern synonyms will result in more efficient code, too, but I haven't checked that. And even if it was: Perhaps GHC can be tweaked to treat both versions above in the same way (I can see no reason why this shouldn't be possible, but perhaps I'm wrong). Regarding readability: The version with pattern synonyms *is* slightly more readable, but not so much that it would warrant dropping slightly outdated GHCs.

Regarding the 'half' package: I've just seen that it should work with any GHC 7.x now, so this decision can be decoupled from the pattern synonym issue. Perhaps I should release a new, only slightly incompatible OpenGLRaw version using 'half'? Although GLhalf is part of OpenGL core since 3.0, it is only used in very few non-central places (GL_ARB_half_float_pixel, GL_ARB_half_float_vertex, and GL_NV_half_float). So the resulting breakage will probably be very low.

Regarding the module prefix: I'm not sure if it's worth making this breaking change alone, probably this should only be done in conjunction with the introduction of pattern synonyms. But other opinions would be valuable here, too.

[...] As an aside regarding the wiki discussion, I don't really see how
there's a sane way to have a combined low-level API for WebGL and full
OpenGL. [...]

As already mentioned in more detail on the Wiki, the plan to combine OpenGL and WebGL in a single package is doomed: Different values for the same token, different contents of the extensions, different ways to retrieve the entry points. It's a pity, but that's how it is...

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[Sven Panne-2]

2015-10-01 11:01 GMT+02:00 Oliver Charles <[hidden email]>:

[...] However, it's a lot more significant if you want to do something like:

foo x = doSomething (case x of ...)

Without pattern synonyms, you either have

foo x = doSomething x'

  where x' | x == ... = ...

or

{-# LANGUAGE MultiWayIf #-}

foo x = doSomething (if | x == ... -> ...)

Or simply in plain old Haskell (basically the desugaring of the multi-way-if):

   foo x = doSomething (case () of

                                     _ | x == gl_BAR -> expr1

                                        | x == gl_BAZ -> expr2

                                        | otherwise -> expr3)

Compared to:

   foo x = doSomething (case x of

                                      GL_BAR -> expr1

                                      GL_BAZ -> expr2

                                      _ .> expr3)

it doesn't really look *that* much different IMHO, given the high price one has to pay for a tiny improvement in readability. But that's my personal, more conservative view of things, and I'm here to see what other people prefer.Alas, up to now, this is not very conclusive... :-/

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[Sven Panne-2]

FYI: I've released a new OpenGLRaw version 3.0.0.0 which is now quite close to the gl package. The changes:

  * Use pattern synonyms for OpenGL enums.

  * Changed module name prefix from Graphics.Rendering.OpenGL.Raw to Graphics.GL.

  * Use slightly different type synonyms for GL type (introducing Fixed on the way):

      * CDouble => Double (for GLclampd, GLdouble)

      * CFloat => Float (for GLclampf, GLfloat)

      * CInt => Fixed (for GLclampx, GLfixed)

      * CInt => Int32 (for GLint, GLsizei)

      * CSChar => Int8 (for GLbyte)

      * CShort => Int16 (for GLshort)

      * CUChar => Word8 (for GLboolean, GLubyte)

      * CUInt => Word32 (for GLbitfield, GLenum, GLhandleARB, GLuint)

      * CUShort => Word16 (for GLushort)

There are still a few minor differences between OpenGLRaw and gl (see https://github.com/haskell-opengl/OpenGLRaw/wiki/Merging-OpenGLRaw-and-gl), but nothing serious: As a test, I modified the luminance package to make it compatible with the new OpenGLRaw, and the diff is really small (see https://github.com/phaazon/luminance/pull/39). So I think that the gl package can be retired, but that's of course totally up to Edward and Gabríel. A few remarks:

  * Using pattern synonyms means losing support for GHC < 7.8, which I consider OK now that 8.0 is coming soon. But to be sure, there is a branch ("classic") for the previous OpenGLRaw API if the need for minor changes/bug fixes arises.

  * To stay consistent, GLURaw has been changed in a similar way.

  * The OpenGL package has been adapted to use the new APIs internally, but its external API is still the same.

Cheers,

   S.

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[Sven Panne-2]

After some discussions and looking at the diffs needed to make the `luminance` package and Oliver Charles' SSAO-example use OpenGLRaw instead of gl, I decided to change the types of GL_TRUE and GL_FALSE from GLenum to GLboolean. When these enums are used as parameters, their type is almost always GLboolean, with glClampColor being the only exception. Some general retrieval functions like glProgramiv return boolean values as GLint, but that seems to be the rarer use case. OpenGL is very loosely typed, so you will have to use some fromIntegral calls, even if the enum patterns were more polymorphic. After several decades of computer science and having seen tons of bugs caused by them, I have a strong aversion to implicit conversions, so I'm still convinced that the monomorphic enums are the right thing. :-)

I made a new release of OpenGLRaw (https://github.com/haskell-opengl/OpenGLRaw/releases/tag/v3.1.0.0), which in addition to this typing change contains some "mkFoo" synonyms for the "makeFoo" functions, too, a difference between OpenGLRaw and gl I didn't notice earlier.

Cheers,

   S.

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[Sven Panne-2]

2016-01-10 21:56 GMT+01:00 Oliver Charles <[hidden email]>:

I'm not really convinced by this. This change introduced an inconsistency and duplication, but doesn't really solve the problem. I already found another enum that has this problem (GL_LINEAR), and I hardly suggest introducing GL_LINEAR to work around that.

GL_LINEAR as a parameter is sometimes used as a GLenum (see e.g. glBlitFramebuffer) and sometimes as a GLint (see e.g. glGetTextureParameteriv), and there is no clear winner.

 

While I agree that OpenGL is barely typed *statically*, there is a lot of runtime type checking. In practice o always develop with KHR debug as an extension or replay via apitrace, and this always checks ebum values for validity.

Yes, using a debug context + glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS) + glDebugMessageCallback during development is always a good idea. Apart from the stateful nature of the API ("this and that is only allowed when we are in state foobar etc."), the whole notion of profiles and extensions makes it fundamentally impossible to have a 100% type-safe API. You can't even e.g. statically tell which set of enums is allowed as a parameter for a given function.

I think OpenGLRaw would be more practical with gl-style polymorphic patterns

As I said in my previous email: Whenever you use the OpenGL API directly (be it via OpenGLRaw or gl), you *will* have lots of 'fromIntegral's, and the patterns don't make much of a difference. A quick grep showed that your SSAO-example project has 33 fromIntegral calls, and only 2 are caused by the patterns being monomorphic. The luminance package is even more extreme in this respect: It contains 188 fromIntegral calls, and only 2 are caused by the monomorphic patterns. (I may be off by small amount, but that doesn't really change the fact.) So in a nutshell: This is a non-issue in practice and mostly a bikeshedding discussion, and I won't change that aspect of the binding.

Cheers,

   S.

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