Fix imageStore output for types other than 4-vectors (#622)

Fixes issue #620

Given a `RWTexture*` store operation like:

```hlsl
RWTexture3D a<float>;
...
float x = 1.0f;
a[crd] = x;
```

We were generating output GLSL like:

```glsl
layout(rgba32f) image3D a;
...
float x = 1.0f;
imageStore(a, crd, x);
```

but in that case, the `imageStore` operation expected a `vec4` and not a `float` for the last argument, and we fail GLSL compilation.

This change extends our handling of the `imageStore` operation in the stdlib so that we pad out the last argument if it is not a 4-vector.

We also flesh out the code that was picking a `layout(...)` modifier for image formats so that it doesn't just blindly use `layout(rgba32f)` and instead takes the element type fed to `RWTexture3D<...>` into account.

With these two changes, the above HLSL/Slang code now translates to:

```glsl
layout(r32f) image3D a;
...
float x = 1.0f;
imageStore(a, crd, vec4(x, float(0), float(0), float(0)));
```

Note that we are padding out the `x` argument to a full vector, and also that we declare the image with `layout(r32f)` to reflect the fact that it has only as single channel.

1 files changed, 1 insertions, 1 deletions

diff --git a/source/slang/core.meta.slang.h b/source/slang/core.meta.slang.h
index 555353c92..0f69d0b5b 100644
--- a/source/slang/core.meta.slang.h
+++ b/source/slang/core.meta.slang.h
@@ -759,7 +759,7 @@ for (int tt = 0; tt < kBaseTextureTypeCount; ++tt)
                     break;
 
                 default:
-                    sb << "__target_intrinsic(glsl, \"imageStore($0, " << ivecN << "($1), $2)\") set;\n";
+                    sb << "__target_intrinsic(glsl, \"imageStore($0, " << ivecN << "($1), $V2)\") set;\n";
 
                     // Note: HLSL doesn't support component-granularity access into typed UAVs,
                     // and also doesn't support atomic operations on them. As such, there should