static const global variables get transpiled to const in wgsl which dont support indexing

[zurrutik]

I created the following shader in slang:

//////////////constants
static const float2 positions[] = {
    float2( -1.0f, -1.0f ),
    float2(  1.0f, -1.0f ),
    float2(  1.0f,  1.0f ),
    float2( -1.0f,  1.0f )
};

static const float2 texCoords[] = {
    float2( 0.0f, 0.0f ),
    float2( 1.0f, 0.0f ),
    float2( 1.0f, 1.0f ),
    float2( 0.0f, 1.0f )
};


//////////////types
struct VertexOutput
{
    float4 position : SV_POSITION;
    float2 texCoord : TEXCOORD;
};

/////////////binding sets
[[vk::binding(0, 0)]] Texture2D tex : register(t0, space0);

////////////vertex shader
[shader("vertex")]
VertexOutput vertexMain( uint vertexID: SV_VertexID )
{
    VertexOutput output;

    output.position = float4( positions[vertexID], 0.0f, 1.0f );
    output.texCoord = texCoords[vertexID];
    
    return output;
}

////////////fragment shader
[shader("fragment")]
float4 fragmentMain( VertexOutput input ) : SV_Target
{
    return 1.0f - tex.Load( int3( int2( input.position.xy ), 0 ) );
}

The problem is that the "static const" global variables get translated to "const" in .wgsl:

const texCoords_0 : array<vec2<f32>, i32(4)> = array<vec2<f32>, i32(4)>( vec2<f32>(0.0f, 0.0f), vec2<f32>(1.0f, 0.0f), vec2<f32>(1.0f, 1.0f), vec2<f32>(0.0f, 1.0f) );
const positions_0 : array<vec2<f32>, i32(4)> = array<vec2<f32>, i32(4)>( vec2<f32>(-1.0f, -1.0f), vec2<f32>(1.0f, -1.0f), vec2<f32>(1.0f, 1.0f), vec2<f32>(-1.0f, 1.0f) );

But unfortunately when I compile the shader I get the following error:

Uncaptured device error: type WGPUErrorType_Validation
 (Validation Error
 
 Caused by:
     In wgpuDeviceCreateShaderModule
 
 Shader validation error:
    ÔöîÔöÇ :15:37
    Ôöé
 15 Ôöé     output_0.position_0 = vec4<f32>(positions_0[vertexID_0], 0.0f, 1.0f);
    Ôöé                                     ^^^^^^^^^^^^^^^^^^^^^^^ naga::Expression [5]
 
 
     Entry point vertexMain at Vertex is invalid
     Expression [5] is invalid
     The expression [4] may only be indexed by a constant
 )

I think its because "const" in .wgsl means more like "constexpr" in C++ rather than "const" therefore it can only be indexed by another "constexpr" variable( which vertexID is not )

If I change texCoords_0 and positions_0 from "const" to "var<private>" it works no problem( I was tempted to use "let" which is supposed to be the equivalent of C++'s "const" but then I get an error ---> Shader '' parsing error: expected global item ('struct', 'const', 'var', 'alias', ';', 'fn') or the end of the file, found 'let'

Could you please fix this issue?? ( or alternatively provide a solution for the problem )

Regards,

[kaizhangNV]

are those messy code
``
ÔöîÔöÇ

generated by slang?

[fairywreath]

You can drop the const and only use static to get var<private> but the output looks like this which is not that nice:

fn _S1( _S2 : ptr<function, array<vec2<f32>, i32(4)>>)
{
    const _S3 : vec2<f32> = vec2<f32>(1.0f, -1.0f);
    const _S4 : vec2<f32> = vec2<f32>(1.0f, 1.0f);
    const _S5 : vec2<f32> = vec2<f32>(-1.0f, 1.0f);
    (*_S2)[i32(0)] = vec2<f32>(-1.0f, -1.0f);
    (*_S2)[i32(1)] = _S3;
    (*_S2)[i32(2)] = _S4;
    (*_S2)[i32(3)] = _S5;
    return;
}
var<private> positions_0 : array<vec2<f32>, i32(4)>;
fn _S6( _S7 : ptr<function, array<vec2<f32>, i32(4)>>)
{
    const _S8 : vec2<f32> = vec2<f32>(1.0f, 0.0f);
    const _S9 : vec2<f32> = vec2<f32>(1.0f, 1.0f);
    const _S10 : vec2<f32> = vec2<f32>(0.0f, 1.0f);
    (*_S7)[i32(0)] = vec2<f32>(0.0f, 0.0f);
    (*_S7)[i32(1)] = _S8;
    (*_S7)[i32(2)] = _S9;
    (*_S7)[i32(3)] = _S10;
    return;
}
var<private> texCoords_0 : array<vec2<f32>, i32(4)>;
struct VertexOutput_0
{
    @builtin(position) position_0 : vec4<f32>,
    @location(0) texCoord_0 : vec2<f32>,
};

[zurrutik]

If i do that then I get the following .wgsl code:

@binding(0) @group(0) var tex_0 : texture_2d<f32>;

fn _S1( _S2 : ptr<function, array<vec2<f32>, i32(4)>>)
{
    const _S3 : vec2<f32> = vec2<f32>(1.0f, -1.0f);
    const _S4 : vec2<f32> = vec2<f32>(1.0f, 1.0f);
    const _S5 : vec2<f32> = vec2<f32>(-1.0f, 1.0f);
    (*_S2)[i32(0)] = vec2<f32>(-1.0f, -1.0f);
    (*_S2)[i32(1)] = _S3;
    (*_S2)[i32(2)] = _S4;
    (*_S2)[i32(3)] = _S5;
    return;
}

var<private> positions_0 : array<vec2<f32>, i32(4)>;

fn _S6( _S7 : ptr<function, array<vec2<f32>, i32(4)>>)
{
    const _S8 : vec2<f32> = vec2<f32>(1.0f, 0.0f);
    const _S9 : vec2<f32> = vec2<f32>(1.0f, 1.0f);
    const _S10 : vec2<f32> = vec2<f32>(0.0f, 1.0f);
    (*_S7)[i32(0)] = vec2<f32>(0.0f, 0.0f);
    (*_S7)[i32(1)] = _S8;
    (*_S7)[i32(2)] = _S9;
    (*_S7)[i32(3)] = _S10;
    return;
}

var<private> texCoords_0 : array<vec2<f32>, i32(4)>;

struct VertexOutput_0
{
    @builtin(position) position_0 : vec4<f32>,
    @location(0) texCoord_0 : vec2<f32>,
};

@vertex
fn vertexMain(@builtin(vertex_index) vertexID_0 : u32) -> VertexOutput_0
{
    var _S11 : array<vec2<f32>, i32(4)>;
    _S1(&(_S11));
    positions_0 = _S11;
    var _S12 : array<vec2<f32>, i32(4)>;
    _S6(&(_S12));
    texCoords_0 = _S12;
    var output_0 : VertexOutput_0;
    output_0.position_0 = vec4<f32>(positions_0[vertexID_0], 0.0f, 1.0f);
    output_0.texCoord_0 = texCoords_0[vertexID_0];
    return output_0;
}

struct pixelOutput_0
{
    @location(0) output_1 : vec4<f32>,
};

struct pixelInput_0
{
    @location(0) texCoord_1 : vec2<f32>,
};

@fragment
fn fragmentMain( _S13 : pixelInput_0, @builtin(position) position_1 : vec4<f32>) -> pixelOutput_0
{
    var _S14 : array<vec2<f32>, i32(4)>;
    _S1(&(_S14));
    positions_0 = _S14;
    var _S15 : array<vec2<f32>, i32(4)>;
    _S6(&(_S15));
    texCoords_0 = _S15;
    var _S16 : vec3<i32> = vec3<i32>(vec2<i32>(position_1.xy), i32(0));
    var _S17 : pixelOutput_0 = pixelOutput_0( vec4<f32>(1.0f) - (textureLoad((tex_0), ((_S16)).xy, ((_S16)).z)) );
    return _S17;
}

And the error I get this time around is this:

(Validation Error

Caused by:
    In wgpuDeviceCreateShaderModule

Shader '' parsing error: expected assignment or increment/decrement, found '_S3'
  ÔöîÔöÇ wgsl:5:11
  Ôöé
5 Ôöé     const _S3 : vec2<f32> = vec2<f32>(1.0f, -1.0f);
  Ôöé           ^^^ expected assignment or increment/decrement


    expected assignment or increment/decrement, found '_S3'
)

Not sure why it prints those funny looking characters...I am using wgpu-native( not sure if its relevant )