GLSL tutorial #19

jkwak-work · 2024-11-21T00:26:38Z

This is a tutorial document for "migrating from glsl".

jkwak-work · 2024-12-10T23:02:12Z

…rk/shader-slang.github.io into doc/migrating_from_glsl

jkwak-work · 2024-12-10T23:10:38Z

The preview page is here.
https://github.com/jkwak-work/shader-slang.github.io/blob/doc/migrating_from_glsl/docs/coming-from-glsl.md

docs/coming-from-glsl.md

cheneym2 · 2024-12-11T00:10:06Z

docs/coming-from-glsl.md

+
+## How to use GLSL shaders as the input
+By default, Slang doesn't recognize GLSL syntax. You need to explicitly enable it with an option, `-allow-glsl` or `-lang glsl`.


That's the options for slangc, maybe include the API options as well?

Curious, is it necessary to add -allow-glsl if your shader has "import glsl;"?

I could give a try and see what the actual behaviors are.
But my understanding is that import glsl just imports the GLSL functions top of what is available as Slang core modules.
It is not enough to allow the shader to use GLSL specific language syntax such as layout(location = 0).
These GLSL keywords are available only when -allow-glsl is used.

I am not clear on what -lang glsl actually does. I thought it is meant to includes -allow-glsl but when I tried last time, I still had to have -allow-glsl.
I will test a bit and update the document.

I don’t think you need -allow-glsl if you have #version 450 declaration in the source file.

-lang glsl does nothing right now so let’s not mention it.

docs/coming-from-glsl.md

csyonghe · 2024-12-12T17:35:03Z

docs/coming-from-glsl.md

+
+## Layout rules
+By default, Slang uses `std430` as the layout rule. You can explicitly specify to use `std140` whenever needed.


This is not true. Uniform buffer defaults to std140, shader storage buffers and structured buffers default to std430.

The example below is using HLSL syntax but this doc is for glsl users, so it seems inappropriate, unless we start with some explanation, such as “to explicitly specify the layout of individual buffers, you can use the Slang syntax when declaring the buffer.”

csyonghe · 2024-12-12T17:35:30Z

docs/coming-from-glsl.md

+StructuredBuffer<T, Std140DataLayout> std140Layout;
+StructuredBuffer<T, Std430DataLayout> std430Layout;
+StructuredBuffer<T, ScalarDataLayout> scalarLayout;


Add a case for specifying layout for a ConstantBuffer<>.

csyonghe · 2024-12-12T17:38:11Z

docs/coming-from-glsl.md

+```
+
+The layout rule can also be changed with options like `-force-glsl-scalar-layout` or `-fvk-use-scalar-layout`.


There is also -fvk-use-dx-layout now. See dxc documentation for what it means.

csyonghe · 2024-12-12T17:40:12Z

docs/coming-from-glsl.md

+
+## Matrix
+Even though GLSL claims to use "Column-major", it is mostly nomenclature when it comes to the shader-side implementation. For this reason, `matXxY` and `floatXxY` can be used interchangeably in Slang.


We can just say matNxM is a typedef to floatNxM.

csyonghe · 2024-12-12T17:41:03Z

docs/coming-from-glsl.md

+GLSL requires an entry point to be named `main`. This requirement prevents a shader file from having more than one entry point, unlike other shading languages such as HLSL and Metal.
+
+But this requirement doesn't apply when using Slang with the option `-allow-glsl`. In other words, you can define multiple entry points in the same shader file.


Talk about -fvk-use-EntryPoint-name here.

csyonghe · 2024-12-12T17:47:16Z

docs/coming-from-glsl.md

+## Overview
+Slang allows developers to use GLSL syntax as input shaders. It provides an easy transition from your existing GLSL-based system to the Slang system. This document provides information that users may want to know when migrating from a GLSL-based system to the Slang system.


… when migrating a glsl shader code base to Slang.

csyonghe · 2024-12-12T17:48:53Z

docs/coming-from-glsl.md

+
+## How to use GLSL shaders as the input
+By default, Slang doesn't recognize GLSL syntax. You need to explicitly enable it with an option, `-allow-glsl` or `-lang glsl`.


I don’t think you need -allow-glsl if you have #version 450 declaration in the source file.

csyonghe · 2024-12-12T17:49:11Z

docs/coming-from-glsl.md

+
+## How to use GLSL shaders as the input
+By default, Slang doesn't recognize GLSL syntax. You need to explicitly enable it with an option, `-allow-glsl` or `-lang glsl`.


-lang glsl does nothing right now so let’s not mention it.

csyonghe · 2024-12-12T17:56:02Z

docs/coming-from-glsl.md

+For people who are interested in more details of how GLSL functions are translated, please refer to [glsl.meta.slang](https://github.com/shader-slang/slang/blob/master/source/slang/glsl.meta.slang).
+
+## How to use GLSL shaders as input


Add a section on the support level of glsl input:

The support for GLSL input in the slang compiler is best-effort rather than spec-complete. The Slang compiler understands many but not all GLSL syntax. Slang is not a drop-in replacement for any existing GLSL compiler. Instead, the intention is to make transition from glsl to Slang easy by allowing mixing GLSL syntax and Slang syntax so the user does not need to modify every line of code before they can use Slang features. The user is still expected to migrate from unsupported GLSL syntax before they can be accepted by the Slang compiler.

Most of the unsupported areas of GLSL syntax are around global parameter or layout declarations. We expect most functions written in GLSL to just work in Slang.

csyonghe · 2024-12-12T18:00:53Z

docs/coming-from-glsl.md

+
+For a more detailed explanation about the matrix layout, please check another document, [Handling Matrix Layout Differences on Different Platforms](https://shader-slang.com/slang/user-guide/a1-01-matrix-layout.html).
+


Also need a section to talk about the difference of operator ==, * between glsl and HLSL, and how -allow-glsl/#version/import glsl changes that default behavior.

And a section on how shader storage buffers are parsed and supported.

Show the glsl syntax and equivalent slang code for constant buffers, structured buffers and storage buffers, so people know how to migrate the code to slang if they want to do so.

Initial writing

8c19b34

jkwak-work self-assigned this Nov 21, 2024

jkwak-work added 2 commits December 10, 2024 15:00

Adding explanations about the matrix

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Fix typo

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jkwak-work added 3 commits December 10, 2024 15:06

Merge branch 'main' into doc/migrating_from_glsl

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Rename the subtitle "Matrix layout" to "Matrix"

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Merge branch 'doc/migrating_from_glsl' of https://github.com/jkwak-wo…

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…rk/shader-slang.github.io into doc/migrating_from_glsl

jkwak-work changed the title ~~[WIP] GLSL tutorial~~ GLSL tutorial Dec 10, 2024

jkwak-work marked this pull request as ready for review December 10, 2024 23:14

jkwak-work requested review from csyonghe and cheneym2 December 10, 2024 23:15

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GLSL tutorial #19

GLSL tutorial #19

jkwak-work commented Nov 21, 2024 •

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		## How to use GLSL shaders as the input
		By default, Slang doesn't recognize GLSL syntax. You need to explicitly enable it with an option, `-allow-glsl` or `-lang glsl`.


		## Layout rules
		By default, Slang uses `std430` as the layout rule. You can explicitly specify to use `std140` whenever needed.

		```

		The layout rule can also be changed with options like `-force-glsl-scalar-layout` or `-fvk-use-scalar-layout`.


		## Matrix
		Even though GLSL claims to use "Column-major", it is mostly nomenclature when it comes to the shader-side implementation. For this reason, `matXxY` and `floatXxY` can be used interchangeably in Slang.

		GLSL requires an entry point to be named `main`. This requirement prevents a shader file from having more than one entry point, unlike other shading languages such as HLSL and Metal.

		But this requirement doesn't apply when using Slang with the option `-allow-glsl`. In other words, you can define multiple entry points in the same shader file.

		## Overview
		Slang allows developers to use GLSL syntax as input shaders. It provides an easy transition from your existing GLSL-based system to the Slang system. This document provides information that users may want to know when migrating from a GLSL-based system to the Slang system.

		For people who are interested in more details of how GLSL functions are translated, please refer to [glsl.meta.slang](https://github.com/shader-slang/slang/blob/master/source/slang/glsl.meta.slang).

		## How to use GLSL shaders as input


		For a more detailed explanation about the matrix layout, please check another document, [Handling Matrix Layout Differences on Different Platforms](https://shader-slang.com/slang/user-guide/a1-01-matrix-layout.html).

GLSL tutorial #19

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GLSL tutorial #19

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jkwak-work commented Nov 21, 2024 • edited Loading

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jkwak-work commented Nov 21, 2024 •

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