Add Transform For External Textures

Adds a transform to reclassify single-plane texture_external types into 2d sampled textures. Adds a unit test for the transform.

Bug: dawn:728
Change-Id: Id1f88565aeacbfea47b140181c78ad122edbdae8
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/49641
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

src/BUILD.gn

@@ -515,6 +515,8 @@ libtint_source_set("libtint_core_all_src") {
     "transform/decompose_storage_access.h",
     "transform/emit_vertex_point_size.cc",
     "transform/emit_vertex_point_size.h",
+    "transform/external_texture_transform.cc",
+    "transform/external_texture_transform.h",
     "transform/first_index_offset.cc",
     "transform/first_index_offset.h",
     "transform/manager.cc",

src/CMakeLists.txt

@@ -271,6 +271,8 @@ set(TINT_LIB_SRCS
   transform/decompose_storage_access.h
   transform/emit_vertex_point_size.cc
   transform/emit_vertex_point_size.h
+  transform/external_texture_transform.cc
+  transform/external_texture_transform.h
   transform/first_index_offset.cc
   transform/first_index_offset.h
   transform/manager.cc
@@ -796,6 +798,7 @@ if(${TINT_BUILD_TESTS})
       transform/canonicalize_entry_point_io_test.cc
       transform/decompose_storage_access_test.cc
       transform/emit_vertex_point_size_test.cc
+      transform/external_texture_transform_test.cc
       transform/first_index_offset_test.cc
       transform/renamer_test.cc
       transform/single_entry_point.cc

src/transform/external_texture_transform.cc

@@ -0,0 +1,59 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/transform/external_texture_transform.h"
+#include "src/program_builder.h"
+
+namespace tint {
+namespace transform {
+
+ExternalTextureTransform::ExternalTextureTransform() = default;
+ExternalTextureTransform::~ExternalTextureTransform() = default;
+
+Output ExternalTextureTransform::Run(const Program* in, const DataMap&) {
+  ProgramBuilder out;
+  CloneContext ctx(&out, in);
+
+  // Scan the AST nodes for external texture declarations.
+  for (auto* node : ctx.src->ASTNodes().Objects()) {
+    if (auto* var = node->As<ast::Variable>()) {
+      if (var->type().ast->Is<ast::ExternalTexture>()) {
+        // Replace a single-plane external texture with a 2D, f32 sampled
+        // texture.
+        auto* newAstType = ctx.dst->create<ast::SampledTexture>(
+            ast::TextureDimension::k2d, ctx.dst->create<ast::F32>());
+        auto* newSemType = ctx.dst->create<sem::SampledTexture>(
+            ast::TextureDimension::k2d, ctx.dst->ty.f32());
+
+        auto clonedSrc = ctx.Clone(var->source());
+        auto clonedSym = ctx.Clone(var->symbol());
+        auto* clonedConstructor = ctx.Clone(var->constructor());
+        auto clonedDecorations = ctx.Clone(var->decorations());
+
+        auto* newVar = ctx.dst->create<ast::Variable>(
+            clonedSrc, clonedSym, var->declared_storage_class(),
+            typ::Type(newAstType, newSemType), var->is_const(),
+            clonedConstructor, clonedDecorations);
+
+        ctx.Replace(var, newVar);
+      }
+    }
+  }
+
+  ctx.Clone();
+  return Output{Program(std::move(out))};
+}
+
+}  // namespace transform
+}  // namespace tint

src/transform/external_texture_transform.h

@@ -0,0 +1,47 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_TRANSFORM_EXTERNAL_TEXTURE_TRANSFORM_H_
+#define SRC_TRANSFORM_EXTERNAL_TEXTURE_TRANSFORM_H_
+
+#include <utility>
+
+#include "src/transform/transform.h"
+
+namespace tint {
+namespace transform {
+
+// Because an external texture is comprised of 1-3 texture views we can simply
+// transform external textures into the appropriate number of sampled textures.
+// This allows us to share SPIR-V/HLSL writer paths for sampled textures instead
+// of adding dedicated writer paths for external textures.
+// ExternalTextureTransform performs this transformation.
+class ExternalTextureTransform : public Transform {
+ public:
+  /// Constructor
+  ExternalTextureTransform();
+  /// Destructor
+  ~ExternalTextureTransform() override;
+
+  /// Runs the transform on `program`, returning the transformation result.
+  /// @param program the source program to transform
+  /// @param data optional extra transform-specific data
+  /// @returns the transformation result
+  Output Run(const Program* program, const DataMap& data = {}) override;
+};
+
+}  // namespace transform
+}  // namespace tint
+
+#endif  // SRC_TRANSFORM_EXTERNAL_TEXTURE_TRANSFORM_H_

src/transform/external_texture_transform_test.cc

@@ -0,0 +1,64 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/transform/external_texture_transform.h"
+
+#include "src/transform/test_helper.h"
+
+namespace tint {
+namespace transform {
+namespace {
+
+using ExternalTextureTransformTest = TransformTest;
+
+TEST_F(ExternalTextureTransformTest, SinglePlane) {
+  auto* src = R"(
+[[builtin(frag_coord)]] var<in> FragCoord : vec4<f32>;
+
+[[group(0), binding(0)]] var s : sampler;
+
+[[group(0), binding(1)]] var t : texture_external;
+
+[[location(0)]] var<out> FragColor : vec4<f32>;
+[[stage(fragment)]]
+fn main() {
+  FragColor = textureSample(t, s, (FragCoord.xy / vec2<f32>(4.0, 4.0)));
+  return;
+}
+)";
+
+  auto* expect = R"(
+[[builtin(frag_coord)]] var<in> FragCoord : vec4<f32>;
+
+[[group(0), binding(0)]] var s : sampler;
+
+[[group(0), binding(1)]] var t : texture_2d<f32>;
+
+[[location(0)]] var<out> FragColor : vec4<f32>;
+
+[[stage(fragment)]]
+fn main() {
+  FragColor = textureSample(t, s, (FragCoord.xy / vec2<f32>(4.0, 4.0)));
+  return;
+}
+)";
+
+  auto got = Run<ExternalTextureTransform>(src);
+
+  EXPECT_EQ(expect, str(got));
+}
+
+}  // namespace
+}  // namespace transform
+}  // namespace tint

test/BUILD.gn

@@ -296,6 +296,7 @@ tint_unittests_source_set("tint_unittests_core_src") {
     "../src/transform/canonicalize_entry_point_io_test.cc",
     "../src/transform/decompose_storage_access_test.cc",
     "../src/transform/emit_vertex_point_size_test.cc",
+    "../src/transform/external_texture_transform_test.cc",
     "../src/transform/first_index_offset_test.cc",
     "../src/transform/renamer_test.cc",
     "../src/transform/single_entry_point_test.cc",