[x3d-public] Mapping SFColor to GLSL - vec3 or vec4?

[John Carlson]

Michalis, I would like the variables taken out of GLSL to be put back into
X3D.   It’s totally ridiculous to maintain O(2*N) shaders when only 2 are
required with N being number of browser vendors.  It would even be better
if a few of the common variables were shared.

So Shaders are pretty much deprecated in favor of PBR.   If you’ve
implemented prismatic PBR, I would be interested...

John

On Sun, Nov 29, 2020 at 3:19 PM Michalis Kamburelis <
michalis.kambi at gmail.com> wrote:

> Hi,
>
> This is a question to X3D implementors that support GLSL shaders (that
> is, "ComposedShader" node with language="GLSL"). With custom fields in
> ComposedShader mapping to GLSL uniform values. (See
> https://castle-engine.io/x3d_implementation_shaders.php for CGE docs.)
>
> Do you map SFColor to vec3 or vec4 in GLSL?
>
> Similarly, do you map MFColor to vec3[] or vec4[] in GLSL?
>
> The reason why I'm asking:
>
> - The X3D specification 3.3 says to map SFColor / MFColor to vec4 /
> vec4[] in GLSL. See "I.4.2 X3D Field types to GLSL data types",
>
> https://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/shaders_glsl.html#Otherfields
> . The X3Dv4 (latest WD2) doesn't change it.
>
> - However, SFColor is an RGB color. That is, it doesn't contain alpha
> value. (We have dedicated SFColorRGBA for a color with alpha
> information.) Same goes for MFColor -- it's a list of RGB colors.
>
> - So it would be much more natural to map SFColor to vec3, and MFColor
> to vec3[]. In case of large MFColor arrays, it would be also more
> optimal, since you pass 3/4 less data to the GPU.
>
> - So far, for a long time, view3dscene / Castle Game Engine
> implemented the X3D spec literally, and we mapped SFColor / MFColor to
> vec4 / vec4[]. But it is really unexpected for authors (costed me
> quite some time recently to figure out "why do I have an error here, I
> send SFColor to vec3, it should work..."). And it is inefficient, if
> you think about large MFColor arrays.
>
> - So I'm curious, what others (X3DOM? FreeWRL? etc.) do. If some /
> most of the actual implementations map SFColor / MFColor -> vec3 /
> vec3[], then maybe we can just fix the specification, to say something
> better?
>
> Regards,
> Michalis
>
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