[HOpenGL] 2D textures with OpenGL and GLUT

[Elise Huard]

I wanted to thank you, because pointing to unsafeCoerce was a nice bit
of serendipity.  I'll admit I thought it was nitpicking initially, but
I did a quick pass at cleaning things up last week after your mail
(not perfect, but this was a prototype so I'm not looking for pretty):

https://github.com/elisehuard/game-prototype/commit/5cf85fa60f325dbe610b5e1f017c9427e304daf6

and that fixed the texture mapping!
Consider me informed on that issue :)

(as for which example, I used Redbook4 but I admit to extrapolating a
little, this was my mistake)

Thank you,

On 2 July 2014 13:11, Jason Dagit <dagitj at gmail.com> wrote:
>
>
>
> On Wed, Jul 2, 2014 at 9:33 AM, Elise Huard <elise at jabberwocky.eu> wrote:
>>
>> Hi Jason,
>> thanks for taking the time to answer.
>> So trying to read between the lines:
>> - do you have any _working_ examples of texture mapping with OpenGLRaw
>> and low-level Haskell I could have a look at? (anything would help at
>> this point)
>
>
> I do. I converted some of the old nehe tutorials:
> https://github.com/dagit/nehe-tuts
>
> If you look through the history you can find examples that use a very very
> old version of OpenGL (instead of OpenGLRaw). The OpenGL style in those
> examples is old and no longer the recommended way. The examples use
> immediate mode which is now deprecated in favor of shaders.
>
> I think lesson 6 makes a cube and throws some textures on it. The lesson
> numbers are meant to match these:
>   * http://nehe.gamedev.net/tutorial/lessons_01__05/22004/
>   * http://nehe.gamedev.net/tutorial/lessons_06__10/17010/
>
>
>>
>> - do you think the unsafeCoerce (which I borrowed from examples) that
>> transform CpFloat to GLdouble might be the issue, or is this just a
>> general stylistic comment?
>
>
> Not just stylistic. As for correctness, I think the answer varies by
> platform. Specifically, I think CFloat is not required to match GLdouble in
> size (in fact, doubles should be expected to be twice as big). While both
> types should correspond to IEEE 754 floats the bit width is very likely
> different and that could easily cause the interpretation of the values to go
> wonky. Imagine passing 64bits when only the first 32bits correspond to a
> valid number or truncating a 64bit value to 32bits.
>
> Which examples use unsafeCoerce for this? I'm just sort of curious so I can
> recommend people not to use them :)
>