[spv-in] sampling from depth textures returns a scalar and is splatted

CHANGELOG.md

@@ -99,6 +99,7 @@ By @bradwerth [#6216](https://github.com/gfx-rs/wgpu/pull/6216).
 
 #### Naga
 
+- SPIR-V frontend splats depth texture sample and load results. Fixes [issue #4551](https://github.com/gfx-rs/wgpu/issues/4551). By @schell in [#6384](https://github.com/gfx-rs/wgpu/pull/6384).
 - Accept only `vec3` (not `vecN`) for the `cross` built-in. By @ErichDonGubler in [#6171](https://github.com/gfx-rs/wgpu/pull/6171).
 - Configure `SourceLanguage` when enabling debug info in SPV-out. By @kvark in [#6256](https://github.com/gfx-rs/wgpu/pull/6256).
 - Per-polygon and flat inputs should not be considered subgroup uniform. By @magcius in [#6276](https://github.com/gfx-rs/wgpu/pull/6276).

naga/src/front/spv/image.rs

@@ -377,36 +377,54 @@ impl<I: Iterator<Item = u32>> super::Frontend<I> {
  let coord_handle =
  self.get_expr_handle(coordinate_id, coord_lexp, ctx, emitter, block, body_idx);
  let coord_type_handle = self.lookup_type.lookup(coord_lexp.type_id)?.handle;
- let (coordinate, array_index) = match ctx.type_arena[image_ty].inner {
+ let (coordinate, array_index, is_depth) = match ctx.type_arena[image_ty].inner {
  crate::TypeInner::Image {
  dim,
  arrayed,
- class: _,
- } => extract_image_coordinates(
- dim,
- if arrayed {
- ExtraCoordinate::ArrayLayer
- } else {
- ExtraCoordinate::Garbage
- },
- coord_handle,
- coord_type_handle,
- ctx,
- ),
+ class,
+ } => {
+ let (coord, array_index) = extract_image_coordinates(
+ dim,
+ if arrayed {
+ ExtraCoordinate::ArrayLayer
+ } else {
+ ExtraCoordinate::Garbage
+ },
+ coord_handle,
+ coord_type_handle,
+ ctx,
+ );
+ (coord, array_index, class.is_depth())
+ }
  _ => return Err(Error::InvalidImage(image_ty)),
  };
 
- let expr = crate::Expression::ImageLoad {
+ let image_load_expr = crate::Expression::ImageLoad {
  image: image_lexp.handle,
  coordinate,
  array_index,
  sample,
  level,
  };
+ let image_load_handle = ctx
+ .expressions
+ .append(image_load_expr, self.span_from_with_op(start));
+
+ let handle = if is_depth {
+ let splat_expr = crate::Expression::Splat {
+ size: crate::VectorSize::Quad,
+ value: image_load_handle,
+ };
+ ctx.expressions
+ .append(splat_expr, self.span_from_with_op(start))
+ } else {
+ image_load_handle
+ };
+
  self.lookup_expression.insert(
  result_id,
  LookupExpression {
- handle: ctx.expressions.append(expr, self.span_from_with_op(start)),
+ handle,
  type_id: result_type_id,
  block_id,
  },
@@ -593,11 +611,12 @@ impl<I: Iterator<Item = u32>> super::Frontend<I> {
  ref other => return Err(Error::InvalidGlobalVar(other.clone())),
  }
 
- let ((coordinate, array_index), depth_ref) = match ctx.type_arena[image_ty].inner {
+ let ((coordinate, array_index), depth_ref, is_depth) = match ctx.type_arena[image_ty].inner
+ {
  crate::TypeInner::Image {
  dim,
  arrayed,
- class: _,
+ class,
  } => (
  extract_image_coordinates(
  dim,
@@ -642,6 +661,7 @@ impl<I: Iterator<Item = u32>> super::Frontend<I> {
  None => None,
  }
  },
+ class.is_depth(),
  ),
  _ => return Err(Error::InvalidImage(image_ty)),
  };
@@ -656,10 +676,21 @@ impl<I: Iterator<Item = u32>> super::Frontend<I> {
  level,
  depth_ref,
  };
+ let image_sample_handle = ctx.expressions.append(expr, self.span_from_with_op(start));
+ let handle = if is_depth && depth_ref.is_none() {
+ let splat_expr = crate::Expression::Splat {
+ size: crate::VectorSize::Quad,
+ value: image_sample_handle,
+ };
+ ctx.expressions
+ .append(splat_expr, self.span_from_with_op(start))
+ } else {
+ image_sample_handle
+ };
  self.lookup_expression.insert(
  result_id,
  LookupExpression {
- handle: ctx.expressions.append(expr, self.span_from_with_op(start)),
+ handle,
  type_id: result_type_id,
  block_id,
  },

naga/src/proc/mod.rs

@@ -622,6 +622,10 @@ impl super::ImageClass {
  crate::ImageClass::Storage { .. } => false,
  }
  }
+
+ pub const fn is_depth(self) -> bool {
+ matches!(self, crate::ImageClass::Depth { .. })
+ }
 }
 
 impl crate::Module {