[fpc-devel] OpenGL 3.3 Core

[Kostas Michalopoulos]

The biggest problem you may have with this is requesting a post 2.1 context
in Mac OS X since Apple decided to create a schism in versioning and only
supports either 2.1 and below or 3.2 core and above. They do not have
ARB_compatibility.

Same with Mesa, meaning that on Linux you can use either 2.1 and below or
3.x core and above if you use the AMDGPU or Intel drivers (AMDGPU-Pro and
of course Nvidia drivers support the entire OpenGL).

>From a quick look at the source, for Mac OS X only the Cocoa backend
supports versioning and for Linux only GTK (Qt doesn't).

Note that there is no explicit way with TOpenGLControl to request the
profile, meaning that under GLX (Linux, GTK2) you always get the core
profile (as per the GLX_ARB_create_context spec) *unless* you ask for 3.0
or less and you *may* get a compatibility profile you 3.1. With 3.2 you
always get core.

This is a cross-platform issue since if you specify a post 3.2 or above
profile in Windows, Carbon or Qt you do not get a core profile but a
compatibility one (in Carbon and Qt you will get a 2.1 profile in some GPU
drivers - like AMDGPU and Intel - even if you ask for a 3.2 since the
requested version is ignored and these drivers do not support compatibility
profiles). This means that if you accidentally use deprecated functionality
and you develop under Windows you wont notice it until you try the program
under Linux or Mac OS X. Also it can be a performance issue since IIRC
Nvidia has said that requesting a core profile will make the driver do
extra checks to make sure you are not using deprecated functionality.

I think the control should gain a Profile attribute to solve this. And
while at it, also a ForwardCompatible attribute for debugging (forward
compatible contexts disable any deprecated functionality, but they can also
slow down rendering due to extra tests, so they are only good for debugging
code).


On Fri, May 26, 2017 at 12:51 PM, Michalis Kamburelis <
michalis.kambi at gmail.com> wrote:

> 2017-05-21 22:38 GMT+02:00 Mathias <m_burkhard at gmx.ch>:
> > Is there an option with Lazarus own board means to activate the OpenGL
> 3.3
> > core mode. Or is it enough for me to do the following?
> >
> >   OpenGLControl.OpenGLMajorVersion := 3;
> >   OpenGLControl.OpenGLMinorVersion := 3;
> >
>
> These TOpenGLControl properties are passed to the underlying API to
> indicate that you want a context that supports this specific OpenGL
> version. So, yes, this is the way to get OpenGL 3.3 context.
>
> However, it's not implemented on all platforms. As far as I see, only
> the GTK widgetset actually uses the Major/MinorVersion, other
> widgetsets simply ignore it.
>
> But in practice, you will also get a 3.3 context without requesting
> it, if your OpenGL supports it, and it has ARB_compatibility. See
> https://www.khronos.org/opengl/wiki/Core_And_Compatibility_in_Contexts
> about the gory details.
>
> Regards,
> Michalis
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