# Validate HLSL grammar in command line

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Category : GPU Programming

HLSL, a.k.a. High-level shader language, is used in Unity.

One can write the shader in Unity (with VS or VSCode) and compile it automatically in Unity. If there’s any error in the shader code, the error message will show up in the Unity console.

However, since I am using a Linux, I can’t debug the shader in Unity. So I turn to a light-weight tool called SHADERed. One can install the SHADERed plug-in in VSCode along with SHADERed, and voilà, we can debug the shader code!

So we can write HLSL in VSCode and SHADERed first, and then copy it to Unity shader and modify it to be compatible.

Here is a cool video shows how to do the modification, it even works with GLSL. Youtube: How to convert a shader from ShaderToy to Unity

Now my problem was that SHADERed won’t show the detailed compilation error if there’s any error in the shader code. It just says, “Can not display preview - there are some errors you should fix.”

So I digged in a bit, and realized that both Unity and SHADERed use glslang to compile the shader code.

Luckily, glslang provide a standalone executable that can compile the shader code as a showcase of how to use the glslang API. It is called glslangValidator. I am on Ubuntu, so I can get this tool by simply apt install glslang-tools.

So for example we want to validate this piece of fragment shader named 2d_SimplePS.hlsl:

cbuffer vars : register(b0)
{
float2 uResolution;
float uTime;
};

float4 main(float4 fragCoord : SV_POSITION) : SV_TARGET
{
float2 uv = fragCoord.xy/uResolution;
uv -= .5;
uv *= uResolution.x/uResolution.y;
here is an intentional error;
float4 color = float4(uv.x, uv.y, 1, 1);
return color;
}


And we use the command:

# look it up using man glslangValidator
glslangValidator -S frag -D --client vulkan100 -e frag 2d_SimplePS.hlsl


and the compiler will show the error message:

2d_SimplePS.hlsl
ERROR: 2d_SimplePS.hlsl:12: 'here' : unknown variable
ERROR: 2d_SimplePS.hlsl:12: ';' : Expected
2d_SimplePS.hlsl(12): error at column 11, HLSL parsing failed.
ERROR: 3 compilation errors.  No code generated.

SPIR-V is not generated for failed compile or link


We have the file name, line number, and the detailed error messages. Great!