Bug cross-compiling HLSL to MSL

[DeCarabas]

I have found a case where SDL_shadercross generates invalid MSL from input HLSL.

Specifically, it generates an invalid attribute index for my StructuredBuffer.

I have this shader HLSL:

struct InstanceData {
  float4x4 transform;
};

cbuffer Uniforms : register(b0, space1) {
  float4x4 mvpMatrix;
};

StructuredBuffer<InstanceData> instances : register(t0, space0);

float4 vs_main(float3 pos : TEXCOORD0, uint iid : SV_InstanceID) : SV_Position {
  return mul(mvpMatrix, mul(instances[iid].transform, float4(pos, 1.0)));
}

Texture2D albedo    : register(t0, space2);
SamplerState samp0  : register(s0, space2);
Texture2D lightmap  : register(t1, space2);
SamplerState samp1  : register(s1, space2);

float4 fs_main(float2 uv : TEXCOORD0, float2 lmuv : TEXCOORD1) : SV_Target0 {
  return albedo.Sample(samp0, uv) * lightmap.Sample(samp1, lmuv);
}

I am compiling this to MSL with the following command line:

shadercross repro.hlsl --dest msl --stage vertex --entrypoint vs_main --output repro_vert.metal

This generates the following broken MSL:

#include <metal_stdlib>
#include <simd/simd.h>

using namespace metal;

struct type_Uniforms
{
    float4x4 mvpMatrix;
};

struct InstanceData
{
    float4x4 transform;
};

struct type_StructuredBuffer_InstanceData
{
    InstanceData _m0[1];
};

struct vs_main_out
{
    float4 gl_Position [[position]];
};

struct vs_main_in
{
    float3 in_var_TEXCOORD0 [[attribute(0)]];
};

vertex vs_main_out vs_main(vs_main_in in [[stage_in]], constant type_Uniforms& Uniforms [[buffer(0)]], const device type_StructuredBuffer_InstanceData& instances [[buffer(4294967295)]], uint gl_InstanceIndex [[instance_id]])
{
    vs_main_out out = {};
    out.gl_Position = Uniforms.mvpMatrix * (instances._m0[gl_InstanceIndex].transform * float4(in.in_var_TEXCOORD0, 1.0));
    return out;
}

The thing to see there is the broken buffer on the instances parameter:

vertex vs_main_out vs_main(... const device type_StructuredBuffer_InstanceData& instances [[buffer(4294967295)]], ...)

A workaround seems to be to split the fragment shader and vertex shader into two different files, and compiling them independently.

(Perhaps something in the cross-compiler is accidentally counting things in one when processing the other?)

[feresr]

I'm having a similar (albeit not identical) problem #198

[feresr]

FWIW I can't seem to repro your issue. I get the following output (latest version for shadercross)

cmd: shadercross "$input" $define_arg -e "fs_main" -t $stage -s HLSL -o "$shaderdir/$stage.msl"

#include <metal_stdlib>
#include <simd/simd.h>

using namespace metal;

struct type_Uniforms
{
    float4x4 mvpMatrix;
};

struct InstanceData
{
    float4x4 transform;
};

struct type_StructuredBuffer_InstanceData
{
    InstanceData _m0[1];
};

struct fs_main_out
{
    float4 out_var_SV_Target0 [[color(0)]];
};

struct fs_main_in
{
    float2 in_var_TEXCOORD0 [[user(locn0)]];
    float2 in_var_TEXCOORD1 [[user(locn1)]];
};

fragment fs_main_out fs_main(fs_main_in in [[stage_in]], texture2d<float> albedo [[texture(0)]], texture2d<float> lightmap [[texture(1)]], sampler samp0 [[sampler(0)]], sampler samp1 [[sampler(1)]])
{
    fs_main_out out = {};
    out.out_var_SV_Target0 = albedo.sample(samp0, in.in_var_TEXCOORD0) * lightmap.sample(samp1, in.in_var_TEXCOORD1);
    return out;
}