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From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: comp.arch
Subject: Re: Misc: Applications of small floating point formats.
Date: Sat, 3 Aug 2024 14:33:01 -0700
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On 8/3/2024 1:29 PM, BGB wrote:
> On 8/3/2024 1:44 PM, Chris M. Thomasson wrote:
>> On 8/2/2024 10:33 PM, Lawrence D'Oliveiro wrote:
>>> On Fri, 2 Aug 2024 21:14:33 -0500, BGB wrote:
>>>
>>>> On 8/2/2024 8:35 PM, Lawrence D'Oliveiro wrote:
>>>>
>>>>> On Fri, 2 Aug 2024 17:18:17 -0700, Chris M. Thomasson wrote:
>>>>>
>>>>>> Taking a screen shot? glReadPixels is okay, right?
>>>>>
>>>>> That means grabbing the whole screen, regardless of what else it might
>>>>> be showing, assuming your window it not occluded, and it further
>>>>> assumes you have a screen to grab from. This kind of precludes running
>>>>> the renderer as a batch, background process.
>>>>
>>>> The glReadPixels call doesn't grab an image from the OS desktop, but
>>>> rather from one of the internal framebuffers associated with the OpenGL
>>>> context.
>>>
>>> Still lousy performance, though. That is simply not considered a serious
>>> usage scenario for OpenGL. And not for any other on-screen 3D API, as 
>>> far
>>> as I’m aware.
>>
>> Afaict, it's fine for taking a snapshot. I used it to create the 
>> following animation as a series of frames:
>>
>> Fractal Boom Box:
>>
>> https://youtu.be/n13GHyYEfLA
> 
> Yeah.
> 
> If you want it for a screenshot or final rendered output, it is fine.
> 
> If you want to fetch images to feed back into textures, maybe not so 
> great performance-wise, but if offline rendering and one doesn't have 
> FBOs, it is fine...
> 
> Like, one doesn't need to try to hold 60 fps for their batch renderer or 
> something.

:^) Iirc, taking the screenshots per frame to create an image stack, 
well, it reduced the fps for my scene...


> Only obvious drawbacks I see is mostly:
> One needs an OpenGL implementation (that works to some acceptable level);
> It is not a raytracer, if one wants/cares about raytracing.

One can implement a raytracer in OpenGL for sure, not easy, but doable. 
I think DirectX 12 has support for it directly... Anyway, a fun part is 
using a fragment shader to do some distance estimated ray marching in 
the GPU. I remember that the PlayStation 3 had a "special version" of 
OpenGL. PS5 has something called GNMX. Never used it before.


> But, as I see it, which is "better" more depends on desired use-case:
>    Want "photorealism" or a "realistic" look,
>      use a raytracer/path-tracer;
>    Want something cartoon like, rasterization makes sense.
>      And, as I see it, may actually be preferable in terms of aesthetics.
> 
> If you want bright, brightly colored, and glossy, rasterization gives 
> this effect easily. If you want something dimly lit and "grungy", then 
> raytracing is a good fit.
> 
> 
> But, if one wants stylized cartoon-like humanoid characters in a 
> raytraced setting, it looks a bit, off.
> 
> 
> And, likewise, if one wants rasterization, OpenGL serves this use case 
> well.
> 
> And, if you want a raytracer, look elsewhere.

I think compute shaders can be used for some raytracing...

:^)