src/tint/transform/multiplanar_external_texture.cc - dawn - Git at Google

 // 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/tint/transform/multiplanar_external_texture.h"

 #include <string>
 #include <vector>

 #include "src/tint/ast/function.h"
 #include "src/tint/program_builder.h"
 #include "src/tint/sem/call.h"
 #include "src/tint/sem/function.h"
 #include "src/tint/sem/variable.h"

 TINT_INSTANTIATE_TYPEINFO(tint::transform::MultiplanarExternalTexture);
 TINT_INSTANTIATE_TYPEINFO(tint::transform::MultiplanarExternalTexture::NewBindingPoints);

 using namespace tint::number_suffixes;  // NOLINT

 namespace tint::transform {
 namespace {

 /// This struct stores symbols for new bindings created as a result of
 /// transforming a texture_external instance.
 struct NewBindingSymbols {
     Symbol params;
     Symbol plane_0;
     Symbol plane_1;
 };
 }  // namespace

 /// State holds the current transform state
 struct MultiplanarExternalTexture::State {
     /// The clone context.
     CloneContext& ctx;

     /// ProgramBuilder for the context
     ProgramBuilder& b;

     /// Destination binding locations for the expanded texture_external provided
     /// as input into the transform.
     const NewBindingPoints* new_binding_points;

     /// Symbol for the GammaTransferParams
     Symbol gamma_transfer_struct_sym;

     /// Symbol for the ExternalTextureParams struct
     Symbol params_struct_sym;

     /// Symbol for the textureLoadExternal function
     Symbol texture_load_external_sym;

     /// Symbol for the textureSampleExternal function
     Symbol texture_sample_external_sym;

     /// Symbol for the gammaCorrection function
     Symbol gamma_correction_sym;

     /// Storage for new bindings that have been created corresponding to an
     /// original texture_external binding.
     std::unordered_map<const sem::Variable*, NewBindingSymbols> new_binding_symbols;

     /// Constructor
     /// @param context the clone
     /// @param newBindingPoints the input destination binding locations for the
     /// expanded texture_external
     State(CloneContext& context, const NewBindingPoints* newBindingPoints)
         : ctx(context), b(*context.dst), new_binding_points(newBindingPoints) {}

     /// Processes the module
     void Process() {
         auto& sem = ctx.src->Sem();

         // For each texture_external binding, we replace it with a texture_2d<f32>
         // binding and create two additional bindings (one texture_2d<f32> to
         // represent the secondary plane and one uniform buffer for the
         // ExternalTextureParams struct).
         for (auto* global : ctx.src->AST().GlobalVariables()) {
             auto* sem_var = sem.Get<sem::GlobalVariable>(global);
             if (!sem_var->Type()->UnwrapRef()->Is<sem::ExternalTexture>()) {
                 continue;
             }

             // If the attributes are empty, then this must be a texture_external
             // passed as a function parameter. These variables are transformed
             // elsewhere.
             if (global->attributes.IsEmpty()) {
                 continue;
             }

             // If we find a texture_external binding, we know we must emit the
             // ExternalTextureParams struct.
             if (!params_struct_sym.IsValid()) {
                 createExtTexParamsStructs();
             }

             // The binding points for the newly introduced bindings must have been
             // provided to this transform. We fetch the new binding points by
             // providing the original texture_external binding points into the
             // passed map.
             BindingPoint bp = sem_var->BindingPoint();

             BindingsMap::const_iterator it = new_binding_points->bindings_map.find(bp);
             if (it == new_binding_points->bindings_map.end()) {
                 b.Diagnostics().add_error(
                     diag::System::Transform,
                     "missing new binding points for texture_external at binding {" +
                         std::to_string(bp.group) + "," + std::to_string(bp.binding) + "}");
                 continue;
             }

             BindingPoints bps = it->second;

             // Symbols for the newly created bindings must be saved so they can be
             // passed as parameters later. These are placed in a map and keyed by
             // the source symbol associated with the texture_external binding that
             // corresponds with the new destination bindings.
             // NewBindingSymbols new_binding_syms;
             auto& syms = new_binding_symbols[sem_var];
             syms.plane_0 = ctx.Clone(global->symbol);
             syms.plane_1 = b.Symbols().New("ext_tex_plane_1");
             b.GlobalVar(syms.plane_1, b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32()),
                         b.Group(AInt(bps.plane_1.group)), b.Binding(AInt(bps.plane_1.binding)));
             syms.params = b.Symbols().New("ext_tex_params");
             b.GlobalVar(syms.params, b.ty.type_name("ExternalTextureParams"),
                         ast::StorageClass::kUniform, b.Group(AInt(bps.params.group)),
                         b.Binding(AInt(bps.params.binding)));

             // Replace the original texture_external binding with a texture_2d<f32>
             // binding.
             auto cloned_attributes = ctx.Clone(global->attributes);
             const ast::Expression* cloned_constructor = ctx.Clone(global->constructor);

             auto* replacement =
                 b.Var(syms.plane_0, b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32()),
                       cloned_constructor, cloned_attributes);
             ctx.Replace(global, replacement);
         }

         // We must update all the texture_external parameters for user declared
         // functions.
         for (auto* fn : ctx.src->AST().Functions()) {
             for (const ast::Variable* param : fn->params) {
                 if (auto* sem_var = sem.Get(param)) {
                     if (!sem_var->Type()->UnwrapRef()->Is<sem::ExternalTexture>()) {
                         continue;
                     }
                     // If we find a texture_external, we must ensure the
                     // ExternalTextureParams struct exists.
                     if (!params_struct_sym.IsValid()) {
                         createExtTexParamsStructs();
                     }
                     // When a texture_external is found, we insert all components
                     // the texture_external into the parameter list. We must also place
                     // the new symbols into the transform state so they can be used when
                     // transforming function calls.
                     auto& syms = new_binding_symbols[sem_var];
                     syms.plane_0 = ctx.Clone(param->symbol);
                     syms.plane_1 = b.Symbols().New("ext_tex_plane_1");
                     syms.params = b.Symbols().New("ext_tex_params");
                     auto tex2d_f32 = [&] {
                         return b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32());
                     };
                     ctx.Replace(param, b.Param(syms.plane_0, tex2d_f32()));
                     ctx.InsertAfter(fn->params, param, b.Param(syms.plane_1, tex2d_f32()));
                     ctx.InsertAfter(fn->params, param,
                                     b.Param(syms.params, b.ty.type_name(params_struct_sym)));
                 }
             }
         }

         // Transform the original textureLoad and textureSampleLevel calls into
         // textureLoadExternal and textureSampleExternal calls.
         ctx.ReplaceAll([&](const ast::CallExpression* expr) -> const ast::CallExpression* {
             auto* call = sem.Get(expr)->UnwrapMaterialize()->As<sem::Call>();
             auto* builtin = call->Target()->As<sem::Builtin>();

             if (builtin && !builtin->Parameters().IsEmpty() &&
                 builtin->Parameters()[0]->Type()->Is<sem::ExternalTexture>() &&
                 builtin->Type() != sem::BuiltinType::kTextureDimensions) {
                 if (auto* var_user = sem.Get<sem::VariableUser>(expr->args[0])) {
                     auto it = new_binding_symbols.find(var_user->Variable());
                     if (it == new_binding_symbols.end()) {
                         // If valid new binding locations were not provided earlier, we
                         // would have been unable to create these symbols. An error
                         // message was emitted earlier, so just return early to avoid
                         // internal compiler errors and retain a clean error message.
                         return nullptr;
                     }
                     auto& syms = it->second;

                     if (builtin->Type() == sem::BuiltinType::kTextureLoad) {
                         return createTexLdExt(expr, syms);
                     }

                     if (builtin->Type() == sem::BuiltinType::kTextureSampleLevel) {
                         return createTexSmpExt(expr, syms);
                     }
                 }

             } else if (call->Target()->Is<sem::Function>()) {
                 // The call expression may be to a user-defined function that
                 // contains a texture_external parameter. These need to be expanded
                 // out to multiple plane textures and the texture parameters
                 // structure.
                 for (auto* arg : expr->args) {
                     if (auto* var_user = sem.Get<sem::VariableUser>(arg)) {
                         // Check if a parameter is a texture_external by trying to find
                         // it in the transform state.
                         auto it = new_binding_symbols.find(var_user->Variable());
                         if (it != new_binding_symbols.end()) {
                             auto& syms = it->second;
                             // When we find a texture_external, we must unpack it into its
                             // components.
                             ctx.Replace(arg, b.Expr(syms.plane_0));
                             ctx.InsertAfter(expr->args, arg, b.Expr(syms.plane_1));
                             ctx.InsertAfter(expr->args, arg, b.Expr(syms.params));
                         }
                     }
                 }
             }

             return nullptr;
         });
     }

     /// Creates the parameter structs associated with the transform.
     void createExtTexParamsStructs() {
         // Create GammaTransferParams struct.
         utils::Vector gamma_transfer_member_list{
             b.Member("G", b.ty.f32()), b.Member("A", b.ty.f32()),      b.Member("B", b.ty.f32()),
             b.Member("C", b.ty.f32()), b.Member("D", b.ty.f32()),      b.Member("E", b.ty.f32()),
             b.Member("F", b.ty.f32()), b.Member("padding", b.ty.u32())};

         gamma_transfer_struct_sym = b.Symbols().New("GammaTransferParams");

         b.Structure(gamma_transfer_struct_sym, gamma_transfer_member_list);

         // Create ExternalTextureParams struct.
         utils::Vector ext_tex_params_member_list{
             b.Member("numPlanes", b.ty.u32()),
             b.Member("doYuvToRgbConversionOnly", b.ty.u32()),
             b.Member("yuvToRgbConversionMatrix", b.ty.mat3x4(b.ty.f32())),
             b.Member("gammaDecodeParams", b.ty.type_name("GammaTransferParams")),
             b.Member("gammaEncodeParams", b.ty.type_name("GammaTransferParams")),
             b.Member("gamutConversionMatrix", b.ty.mat3x3(b.ty.f32()))};

         params_struct_sym = b.Symbols().New("ExternalTextureParams");

         b.Structure(params_struct_sym, ext_tex_params_member_list);
     }

     /// Creates the gammaCorrection function if needed and returns a call
     /// expression to it.
     void createGammaCorrectionFn() {
         gamma_correction_sym = b.Symbols().New("gammaCorrection");

         b.Func(
             gamma_correction_sym,
             utils::Vector{
                 b.Param("v", b.ty.vec3<f32>()),
                 b.Param("params", b.ty.type_name(gamma_transfer_struct_sym)),
             },
             b.ty.vec3<f32>(),
             utils::Vector{
                 // let cond = abs(v) < vec3(params.D);
                 b.Decl(b.Let("cond", b.LessThan(b.Call("abs", "v"),
                                                 b.vec3<f32>(b.MemberAccessor("params", "D"))))),
                 // let t = sign(v) * ((params.C * abs(v)) + params.F);
                 b.Decl(b.Let("t",
                              b.Mul(b.Call("sign", "v"),
                                    b.Add(b.Mul(b.MemberAccessor("params", "C"), b.Call("abs", "v")),
                                          b.MemberAccessor("params", "F"))))),
                 // let f = (sign(v) * pow(((params.A * abs(v)) + params.B),
                 // vec3(params.G))) + params.E;
                 b.Decl(b.Let("f", b.Mul(b.Call("sign", "v"),
                                         b.Add(b.Call("pow",
                                                      b.Add(b.Mul(b.MemberAccessor("params", "A"),
                                                                  b.Call("abs", "v")),
                                                            b.MemberAccessor("params", "B")),
                                                      b.vec3<f32>(b.MemberAccessor("params", "G"))),
                                               b.MemberAccessor("params", "E"))))),
                 // return select(f, t, cond);
                 b.Return(b.Call("select", "f", "t", "cond")),
             });
     }

     /// Constructs a StatementList containing all the statements making up the
     /// bodies of the textureSampleExternal and textureLoadExternal functions.
     /// @param call_type determines which function body to generate
     /// @returns a statement list that makes of the body of the chosen function
     auto createTexFnExtStatementList(sem::BuiltinType call_type) {
         const ast::CallExpression* single_plane_call = nullptr;
         const ast::CallExpression* plane_0_call = nullptr;
         const ast::CallExpression* plane_1_call = nullptr;
         if (call_type == sem::BuiltinType::kTextureSampleLevel) {
             // textureSampleLevel(plane0, smp, coord.xy, 0.0);
             single_plane_call = b.Call("textureSampleLevel", "plane0", "smp", "coord", 0_f);
             // textureSampleLevel(plane0, smp, coord.xy, 0.0);
             plane_0_call = b.Call("textureSampleLevel", "plane0", "smp", "coord", 0_f);
             // textureSampleLevel(plane1, smp, coord.xy, 0.0);
             plane_1_call = b.Call("textureSampleLevel", "plane1", "smp", "coord", 0_f);
         } else if (call_type == sem::BuiltinType::kTextureLoad) {
             // textureLoad(plane0, coords.xy, 0);
             single_plane_call = b.Call("textureLoad", "plane0", "coord", 0_i);
             // textureLoad(plane0, coords.xy, 0);
             plane_0_call = b.Call("textureLoad", "plane0", "coord", 0_i);
             // textureLoad(plane1, coords.xy, 0);
             plane_1_call = b.Call("textureLoad", "plane1", "coord", 0_i);
         } else {
             TINT_ICE(Transform, b.Diagnostics()) << "unhandled builtin: " << call_type;
         }

         return utils::Vector{
             // var color: vec3<f32>;
             b.Decl(b.Var("color", b.ty.vec3(b.ty.f32()))),
             // if ((params.numPlanes == 1u))
             b.If(b.create<ast::BinaryExpression>(
                      ast::BinaryOp::kEqual, b.MemberAccessor("params", "numPlanes"), b.Expr(1_u)),
                  b.Block(
                      // color = textureLoad(plane0, coord, 0).rgb;
                      b.Assign("color", b.MemberAccessor(single_plane_call, "rgb"))),
                  b.Else(b.Block(
                      // color = vec4<f32>(plane_0_call.r, plane_1_call.rg, 1.0) *
                      //         params.yuvToRgbConversionMatrix;
                      b.Assign("color",
                               b.Mul(b.vec4<f32>(b.MemberAccessor(plane_0_call, "r"),
                                                 b.MemberAccessor(plane_1_call, "rg"), 1_f),
                                     b.MemberAccessor("params", "yuvToRgbConversionMatrix")))))),
             // if (params.doYuvToRgbConversionOnly == 0u)
             b.If(b.create<ast::BinaryExpression>(
                      ast::BinaryOp::kEqual, b.MemberAccessor("params", "doYuvToRgbConversionOnly"),
                      b.Expr(0_u)),
                  b.Block(
                      // color = gammaConversion(color, gammaDecodeParams);
                      b.Assign("color", b.Call("gammaCorrection", "color",
                                               b.MemberAccessor("params", "gammaDecodeParams"))),
                      // color = (params.gamutConversionMatrix * color);
                      b.Assign("color",
                               b.Mul(b.MemberAccessor("params", "gamutConversionMatrix"), "color")),
                      // color = gammaConversion(color, gammaEncodeParams);
                      b.Assign("color", b.Call("gammaCorrection", "color",
                                               b.MemberAccessor("params", "gammaEncodeParams"))))),
             // return vec4<f32>(color, 1.f);
             b.Return(b.vec4<f32>("color", 1_f))};
     }

     /// Creates the textureSampleExternal function if needed and returns a call
     /// expression to it.
     /// @param expr the call expression being transformed
     /// @param syms the expanded symbols to be used in the new call
     /// @returns a call expression to textureSampleExternal
     const ast::CallExpression* createTexSmpExt(const ast::CallExpression* expr,
                                                NewBindingSymbols syms) {
         const ast::Expression* plane_0_binding_param = ctx.Clone(expr->args[0]);

         if (expr->args.Length() != 3) {
             TINT_ICE(Transform, b.Diagnostics()) << "expected textureSampleLevel call with a "
                                                     "texture_external to have 3 parameters, found "
                                                  << expr->args.Length() << " parameters";
         }

         // TextureSampleExternal calls the gammaCorrection function, so ensure it
         // exists.
         if (!gamma_correction_sym.IsValid()) {
             createGammaCorrectionFn();
         }

         if (!texture_sample_external_sym.IsValid()) {
             texture_sample_external_sym = b.Symbols().New("textureSampleExternal");

             // Emit the textureSampleExternal function.
             b.Func(
                 texture_sample_external_sym,
                 utils::Vector{
                     b.Param("plane0", b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32())),
                     b.Param("plane1", b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32())),
                     b.Param("smp", b.ty.sampler(ast::SamplerKind::kSampler)),
                     b.Param("coord", b.ty.vec2(b.ty.f32())),
                     b.Param("params", b.ty.type_name(params_struct_sym)),
                 },
                 b.ty.vec4(b.ty.f32()),
                 utils::Vector{
                     createTexFnExtStatementList(sem::BuiltinType::kTextureSampleLevel),
                 });
         }

         const ast::IdentifierExpression* exp = b.Expr(texture_sample_external_sym);
         return b.Call(exp, utils::Vector{
                                plane_0_binding_param,
                                b.Expr(syms.plane_1),
                                ctx.Clone(expr->args[1]),
                                ctx.Clone(expr->args[2]),
                                b.Expr(syms.params),
                            });
     }

     /// Creates the textureLoadExternal function if needed and returns a call
     /// expression to it.
     /// @param expr the call expression being transformed
     /// @param syms the expanded symbols to be used in the new call
     /// @returns a call expression to textureLoadExternal
     const ast::CallExpression* createTexLdExt(const ast::CallExpression* expr,
                                               NewBindingSymbols syms) {
         const ast::Expression* plane_0_binding_param = ctx.Clone(expr->args[0]);

         if (expr->args.Length() != 2) {
             TINT_ICE(Transform, b.Diagnostics())
                 << "expected textureLoad call with a texture_external "
                    "to have 2 parameters, found "
                 << expr->args.Length() << " parameters";
         }

         // TextureLoadExternal calls the gammaCorrection function, so ensure it
         // exists.
         if (!gamma_correction_sym.IsValid()) {
             createGammaCorrectionFn();
         }

         if (!texture_load_external_sym.IsValid()) {
             texture_load_external_sym = b.Symbols().New("textureLoadExternal");

             // Emit the textureLoadExternal function.
             b.Func(
                 texture_load_external_sym,
                 utils::Vector{
                     b.Param("plane0", b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32())),
                     b.Param("plane1", b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32())),
                     b.Param("coord", b.ty.vec2(b.ty.i32())),
                     b.Param("params", b.ty.type_name(params_struct_sym)),
                 },
                 b.ty.vec4(b.ty.f32()),
                 utils::Vector{
                     createTexFnExtStatementList(sem::BuiltinType::kTextureLoad),
                 });
         }

         return b.Call(texture_load_external_sym, plane_0_binding_param, syms.plane_1,
                       ctx.Clone(expr->args[1]), syms.params);
     }
 };

 MultiplanarExternalTexture::NewBindingPoints::NewBindingPoints(BindingsMap inputBindingsMap)
     : bindings_map(std::move(inputBindingsMap)) {}
 MultiplanarExternalTexture::NewBindingPoints::~NewBindingPoints() = default;

 MultiplanarExternalTexture::MultiplanarExternalTexture() = default;
 MultiplanarExternalTexture::~MultiplanarExternalTexture() = default;

 bool MultiplanarExternalTexture::ShouldRun(const Program* program, const DataMap&) const {
     for (auto* node : program->ASTNodes().Objects()) {
         if (auto* ty = node->As<ast::Type>()) {
             if (program->Sem().Get<sem::ExternalTexture>(ty)) {
                 return true;
             }
         }
     }
     return false;
 }

 // Within this transform, an instance of a texture_external binding is unpacked
 // into two texture_2d<f32> bindings representing two possible planes of a
 // single texture and a uniform buffer binding representing a struct of
 // parameters. Calls to textureLoad or textureSampleLevel that contain a
 // texture_external parameter will be transformed into a newly generated version
 // of the function, which can perform the desired operation on a single RGBA
 // plane or on separate Y and UV planes.
 void MultiplanarExternalTexture::Run(CloneContext& ctx, const DataMap& inputs, DataMap&) const {
     auto* new_binding_points = inputs.Get<NewBindingPoints>();

     if (!new_binding_points) {
         ctx.dst->Diagnostics().add_error(
             diag::System::Transform,
             "missing new binding point data for " + std::string(TypeInfo().name));
         return;
     }

     State state(ctx, new_binding_points);

     state.Process();

     ctx.Clone();
 }

 }  // namespace tint::transform
	// 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/tint/transform/multiplanar_external_texture.h"

	#include <string>
	#include <vector>

	#include "src/tint/ast/function.h"
	#include "src/tint/program_builder.h"
	#include "src/tint/sem/call.h"
	#include "src/tint/sem/function.h"
	#include "src/tint/sem/variable.h"

	TINT_INSTANTIATE_TYPEINFO(tint::transform::MultiplanarExternalTexture);
	TINT_INSTANTIATE_TYPEINFO(tint::transform::MultiplanarExternalTexture::NewBindingPoints);

	using namespace tint::number_suffixes; // NOLINT

	namespace tint::transform {
	namespace {

	/// This struct stores symbols for new bindings created as a result of
	/// transforming a texture_external instance.
	struct NewBindingSymbols {
	Symbol params;
	Symbol plane_0;
	Symbol plane_1;
	};
	} // namespace

	/// State holds the current transform state
	struct MultiplanarExternalTexture::State {
	/// The clone context.
	CloneContext& ctx;

	/// ProgramBuilder for the context
	ProgramBuilder& b;

	/// Destination binding locations for the expanded texture_external provided
	/// as input into the transform.
	const NewBindingPoints* new_binding_points;

	/// Symbol for the GammaTransferParams
	Symbol gamma_transfer_struct_sym;

	/// Symbol for the ExternalTextureParams struct
	Symbol params_struct_sym;

	/// Symbol for the textureLoadExternal function
	Symbol texture_load_external_sym;

	/// Symbol for the textureSampleExternal function
	Symbol texture_sample_external_sym;

	/// Symbol for the gammaCorrection function
	Symbol gamma_correction_sym;

	/// Storage for new bindings that have been created corresponding to an
	/// original texture_external binding.
	std::unordered_map<const sem::Variable*, NewBindingSymbols> new_binding_symbols;

	/// Constructor
	/// @param context the clone
	/// @param newBindingPoints the input destination binding locations for the
	/// expanded texture_external
	State(CloneContext& context, const NewBindingPoints* newBindingPoints)
	: ctx(context), b(*context.dst), new_binding_points(newBindingPoints) {}

	/// Processes the module
	void Process() {
	auto& sem = ctx.src->Sem();

	// For each texture_external binding, we replace it with a texture_2d<f32>
	// binding and create two additional bindings (one texture_2d<f32> to
	// represent the secondary plane and one uniform buffer for the
	// ExternalTextureParams struct).
	for (auto* global : ctx.src->AST().GlobalVariables()) {
	auto* sem_var = sem.Get<sem::GlobalVariable>(global);
	if (!sem_var->Type()->UnwrapRef()->Is<sem::ExternalTexture>()) {
	continue;
	}

	// If the attributes are empty, then this must be a texture_external
	// passed as a function parameter. These variables are transformed
	// elsewhere.
	if (global->attributes.IsEmpty()) {
	continue;
	}

	// If we find a texture_external binding, we know we must emit the
	// ExternalTextureParams struct.
	if (!params_struct_sym.IsValid()) {
	createExtTexParamsStructs();
	}

	// The binding points for the newly introduced bindings must have been
	// provided to this transform. We fetch the new binding points by
	// providing the original texture_external binding points into the
	// passed map.
	BindingPoint bp = sem_var->BindingPoint();

	BindingsMap::const_iterator it = new_binding_points->bindings_map.find(bp);
	if (it == new_binding_points->bindings_map.end()) {
	b.Diagnostics().add_error(
	diag::System::Transform,
	"missing new binding points for texture_external at binding {" +
	std::to_string(bp.group) + "," + std::to_string(bp.binding) + "}");
	continue;
	}

	BindingPoints bps = it->second;

	// Symbols for the newly created bindings must be saved so they can be
	// passed as parameters later. These are placed in a map and keyed by
	// the source symbol associated with the texture_external binding that
	// corresponds with the new destination bindings.
	// NewBindingSymbols new_binding_syms;
	auto& syms = new_binding_symbols[sem_var];
	syms.plane_0 = ctx.Clone(global->symbol);
	syms.plane_1 = b.Symbols().New("ext_tex_plane_1");
	b.GlobalVar(syms.plane_1, b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32()),
	b.Group(AInt(bps.plane_1.group)), b.Binding(AInt(bps.plane_1.binding)));
	syms.params = b.Symbols().New("ext_tex_params");
	b.GlobalVar(syms.params, b.ty.type_name("ExternalTextureParams"),
	ast::StorageClass::kUniform, b.Group(AInt(bps.params.group)),
	b.Binding(AInt(bps.params.binding)));

	// Replace the original texture_external binding with a texture_2d<f32>
	// binding.
	auto cloned_attributes = ctx.Clone(global->attributes);
	const ast::Expression* cloned_constructor = ctx.Clone(global->constructor);

	auto* replacement =
	b.Var(syms.plane_0, b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32()),
	cloned_constructor, cloned_attributes);
	ctx.Replace(global, replacement);
	}

	// We must update all the texture_external parameters for user declared
	// functions.
	for (auto* fn : ctx.src->AST().Functions()) {
	for (const ast::Variable* param : fn->params) {
	if (auto* sem_var = sem.Get(param)) {
	if (!sem_var->Type()->UnwrapRef()->Is<sem::ExternalTexture>()) {
	continue;
	}
	// If we find a texture_external, we must ensure the
	// ExternalTextureParams struct exists.
	if (!params_struct_sym.IsValid()) {
	createExtTexParamsStructs();
	}
	// When a texture_external is found, we insert all components
	// the texture_external into the parameter list. We must also place
	// the new symbols into the transform state so they can be used when
	// transforming function calls.
	auto& syms = new_binding_symbols[sem_var];
	syms.plane_0 = ctx.Clone(param->symbol);
	syms.plane_1 = b.Symbols().New("ext_tex_plane_1");
	syms.params = b.Symbols().New("ext_tex_params");
	auto tex2d_f32 = [&] {
	return b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32());
	};
	ctx.Replace(param, b.Param(syms.plane_0, tex2d_f32()));
	ctx.InsertAfter(fn->params, param, b.Param(syms.plane_1, tex2d_f32()));
	ctx.InsertAfter(fn->params, param,
	b.Param(syms.params, b.ty.type_name(params_struct_sym)));
	}
	}
	}

	// Transform the original textureLoad and textureSampleLevel calls into
	// textureLoadExternal and textureSampleExternal calls.
	ctx.ReplaceAll([&](const ast::CallExpression* expr) -> const ast::CallExpression* {
	auto* call = sem.Get(expr)->UnwrapMaterialize()->As<sem::Call>();
	auto* builtin = call->Target()->As<sem::Builtin>();

	if (builtin && !builtin->Parameters().IsEmpty() &&
	builtin->Parameters()[0]->Type()->Is<sem::ExternalTexture>() &&
	builtin->Type() != sem::BuiltinType::kTextureDimensions) {
	if (auto* var_user = sem.Get<sem::VariableUser>(expr->args[0])) {
	auto it = new_binding_symbols.find(var_user->Variable());
	if (it == new_binding_symbols.end()) {
	// If valid new binding locations were not provided earlier, we
	// would have been unable to create these symbols. An error
	// message was emitted earlier, so just return early to avoid
	// internal compiler errors and retain a clean error message.
	return nullptr;
	}
	auto& syms = it->second;

	if (builtin->Type() == sem::BuiltinType::kTextureLoad) {
	return createTexLdExt(expr, syms);
	}

	if (builtin->Type() == sem::BuiltinType::kTextureSampleLevel) {
	return createTexSmpExt(expr, syms);
	}
	}

	} else if (call->Target()->Is<sem::Function>()) {
	// The call expression may be to a user-defined function that
	// contains a texture_external parameter. These need to be expanded
	// out to multiple plane textures and the texture parameters
	// structure.
	for (auto* arg : expr->args) {
	if (auto* var_user = sem.Get<sem::VariableUser>(arg)) {
	// Check if a parameter is a texture_external by trying to find
	// it in the transform state.
	auto it = new_binding_symbols.find(var_user->Variable());
	if (it != new_binding_symbols.end()) {
	auto& syms = it->second;
	// When we find a texture_external, we must unpack it into its
	// components.
	ctx.Replace(arg, b.Expr(syms.plane_0));
	ctx.InsertAfter(expr->args, arg, b.Expr(syms.plane_1));
	ctx.InsertAfter(expr->args, arg, b.Expr(syms.params));
	}
	}
	}
	}

	return nullptr;
	});
	}

	/// Creates the parameter structs associated with the transform.
	void createExtTexParamsStructs() {
	// Create GammaTransferParams struct.
	utils::Vector gamma_transfer_member_list{
	b.Member("G", b.ty.f32()), b.Member("A", b.ty.f32()), b.Member("B", b.ty.f32()),
	b.Member("C", b.ty.f32()), b.Member("D", b.ty.f32()), b.Member("E", b.ty.f32()),
	b.Member("F", b.ty.f32()), b.Member("padding", b.ty.u32())};

	gamma_transfer_struct_sym = b.Symbols().New("GammaTransferParams");

	b.Structure(gamma_transfer_struct_sym, gamma_transfer_member_list);

	// Create ExternalTextureParams struct.
	utils::Vector ext_tex_params_member_list{
	b.Member("numPlanes", b.ty.u32()),
	b.Member("doYuvToRgbConversionOnly", b.ty.u32()),
	b.Member("yuvToRgbConversionMatrix", b.ty.mat3x4(b.ty.f32())),
	b.Member("gammaDecodeParams", b.ty.type_name("GammaTransferParams")),
	b.Member("gammaEncodeParams", b.ty.type_name("GammaTransferParams")),
	b.Member("gamutConversionMatrix", b.ty.mat3x3(b.ty.f32()))};

	params_struct_sym = b.Symbols().New("ExternalTextureParams");

	b.Structure(params_struct_sym, ext_tex_params_member_list);
	}

	/// Creates the gammaCorrection function if needed and returns a call
	/// expression to it.
	void createGammaCorrectionFn() {
	gamma_correction_sym = b.Symbols().New("gammaCorrection");

	b.Func(
	gamma_correction_sym,
	utils::Vector{
	b.Param("v", b.ty.vec3<f32>()),
	b.Param("params", b.ty.type_name(gamma_transfer_struct_sym)),
	},
	b.ty.vec3<f32>(),
	utils::Vector{
	// let cond = abs(v) < vec3(params.D);
	b.Decl(b.Let("cond", b.LessThan(b.Call("abs", "v"),
	b.vec3<f32>(b.MemberAccessor("params", "D"))))),
	// let t = sign(v) * ((params.C * abs(v)) + params.F);
	b.Decl(b.Let("t",
	b.Mul(b.Call("sign", "v"),
	b.Add(b.Mul(b.MemberAccessor("params", "C"), b.Call("abs", "v")),
	b.MemberAccessor("params", "F"))))),
	// let f = (sign(v) * pow(((params.A * abs(v)) + params.B),
	// vec3(params.G))) + params.E;
	b.Decl(b.Let("f", b.Mul(b.Call("sign", "v"),
	b.Add(b.Call("pow",
	b.Add(b.Mul(b.MemberAccessor("params", "A"),
	b.Call("abs", "v")),
	b.MemberAccessor("params", "B")),
	b.vec3<f32>(b.MemberAccessor("params", "G"))),
	b.MemberAccessor("params", "E"))))),
	// return select(f, t, cond);
	b.Return(b.Call("select", "f", "t", "cond")),
	});
	}

	/// Constructs a StatementList containing all the statements making up the
	/// bodies of the textureSampleExternal and textureLoadExternal functions.
	/// @param call_type determines which function body to generate
	/// @returns a statement list that makes of the body of the chosen function
	auto createTexFnExtStatementList(sem::BuiltinType call_type) {
	const ast::CallExpression* single_plane_call = nullptr;
	const ast::CallExpression* plane_0_call = nullptr;
	const ast::CallExpression* plane_1_call = nullptr;
	if (call_type == sem::BuiltinType::kTextureSampleLevel) {
	// textureSampleLevel(plane0, smp, coord.xy, 0.0);
	single_plane_call = b.Call("textureSampleLevel", "plane0", "smp", "coord", 0_f);
	// textureSampleLevel(plane0, smp, coord.xy, 0.0);
	plane_0_call = b.Call("textureSampleLevel", "plane0", "smp", "coord", 0_f);
	// textureSampleLevel(plane1, smp, coord.xy, 0.0);
	plane_1_call = b.Call("textureSampleLevel", "plane1", "smp", "coord", 0_f);
	} else if (call_type == sem::BuiltinType::kTextureLoad) {
	// textureLoad(plane0, coords.xy, 0);
	single_plane_call = b.Call("textureLoad", "plane0", "coord", 0_i);
	// textureLoad(plane0, coords.xy, 0);
	plane_0_call = b.Call("textureLoad", "plane0", "coord", 0_i);
	// textureLoad(plane1, coords.xy, 0);
	plane_1_call = b.Call("textureLoad", "plane1", "coord", 0_i);
	} else {
	TINT_ICE(Transform, b.Diagnostics()) << "unhandled builtin: " << call_type;
	}

	return utils::Vector{
	// var color: vec3<f32>;
	b.Decl(b.Var("color", b.ty.vec3(b.ty.f32()))),
	// if ((params.numPlanes == 1u))
	b.If(b.create<ast::BinaryExpression>(
	ast::BinaryOp::kEqual, b.MemberAccessor("params", "numPlanes"), b.Expr(1_u)),
	b.Block(
	// color = textureLoad(plane0, coord, 0).rgb;
	b.Assign("color", b.MemberAccessor(single_plane_call, "rgb"))),
	b.Else(b.Block(
	// color = vec4<f32>(plane_0_call.r, plane_1_call.rg, 1.0) *
	// params.yuvToRgbConversionMatrix;
	b.Assign("color",
	b.Mul(b.vec4<f32>(b.MemberAccessor(plane_0_call, "r"),
	b.MemberAccessor(plane_1_call, "rg"), 1_f),
	b.MemberAccessor("params", "yuvToRgbConversionMatrix")))))),
	// if (params.doYuvToRgbConversionOnly == 0u)
	b.If(b.create<ast::BinaryExpression>(
	ast::BinaryOp::kEqual, b.MemberAccessor("params", "doYuvToRgbConversionOnly"),
	b.Expr(0_u)),
	b.Block(
	// color = gammaConversion(color, gammaDecodeParams);
	b.Assign("color", b.Call("gammaCorrection", "color",
	b.MemberAccessor("params", "gammaDecodeParams"))),
	// color = (params.gamutConversionMatrix * color);
	b.Assign("color",
	b.Mul(b.MemberAccessor("params", "gamutConversionMatrix"), "color")),
	// color = gammaConversion(color, gammaEncodeParams);
	b.Assign("color", b.Call("gammaCorrection", "color",
	b.MemberAccessor("params", "gammaEncodeParams"))))),
	// return vec4<f32>(color, 1.f);
	b.Return(b.vec4<f32>("color", 1_f))};
	}

	/// Creates the textureSampleExternal function if needed and returns a call
	/// expression to it.
	/// @param expr the call expression being transformed
	/// @param syms the expanded symbols to be used in the new call
	/// @returns a call expression to textureSampleExternal
	const ast::CallExpression* createTexSmpExt(const ast::CallExpression* expr,
	NewBindingSymbols syms) {
	const ast::Expression* plane_0_binding_param = ctx.Clone(expr->args[0]);

	if (expr->args.Length() != 3) {
	TINT_ICE(Transform, b.Diagnostics()) << "expected textureSampleLevel call with a "
	"texture_external to have 3 parameters, found "
	<< expr->args.Length() << " parameters";
	}

	// TextureSampleExternal calls the gammaCorrection function, so ensure it
	// exists.
	if (!gamma_correction_sym.IsValid()) {
	createGammaCorrectionFn();
	}

	if (!texture_sample_external_sym.IsValid()) {
	texture_sample_external_sym = b.Symbols().New("textureSampleExternal");

	// Emit the textureSampleExternal function.
	b.Func(
	texture_sample_external_sym,
	utils::Vector{
	b.Param("plane0", b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32())),
	b.Param("plane1", b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32())),
	b.Param("smp", b.ty.sampler(ast::SamplerKind::kSampler)),
	b.Param("coord", b.ty.vec2(b.ty.f32())),
	b.Param("params", b.ty.type_name(params_struct_sym)),
	},
	b.ty.vec4(b.ty.f32()),
	utils::Vector{
	createTexFnExtStatementList(sem::BuiltinType::kTextureSampleLevel),
	});
	}

	const ast::IdentifierExpression* exp = b.Expr(texture_sample_external_sym);
	return b.Call(exp, utils::Vector{
	plane_0_binding_param,
	b.Expr(syms.plane_1),
	ctx.Clone(expr->args[1]),
	ctx.Clone(expr->args[2]),
	b.Expr(syms.params),
	});
	}

	/// Creates the textureLoadExternal function if needed and returns a call
	/// expression to it.
	/// @param expr the call expression being transformed
	/// @param syms the expanded symbols to be used in the new call
	/// @returns a call expression to textureLoadExternal
	const ast::CallExpression* createTexLdExt(const ast::CallExpression* expr,
	NewBindingSymbols syms) {
	const ast::Expression* plane_0_binding_param = ctx.Clone(expr->args[0]);

	if (expr->args.Length() != 2) {
	TINT_ICE(Transform, b.Diagnostics())
	<< "expected textureLoad call with a texture_external "
	"to have 2 parameters, found "
	<< expr->args.Length() << " parameters";
	}

	// TextureLoadExternal calls the gammaCorrection function, so ensure it
	// exists.
	if (!gamma_correction_sym.IsValid()) {
	createGammaCorrectionFn();
	}

	if (!texture_load_external_sym.IsValid()) {
	texture_load_external_sym = b.Symbols().New("textureLoadExternal");

	// Emit the textureLoadExternal function.
	b.Func(
	texture_load_external_sym,
	utils::Vector{
	b.Param("plane0", b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32())),
	b.Param("plane1", b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32())),
	b.Param("coord", b.ty.vec2(b.ty.i32())),
	b.Param("params", b.ty.type_name(params_struct_sym)),
	},
	b.ty.vec4(b.ty.f32()),
	utils::Vector{
	createTexFnExtStatementList(sem::BuiltinType::kTextureLoad),
	});
	}

	return b.Call(texture_load_external_sym, plane_0_binding_param, syms.plane_1,
	ctx.Clone(expr->args[1]), syms.params);
	}
	};

	MultiplanarExternalTexture::NewBindingPoints::NewBindingPoints(BindingsMap inputBindingsMap)
	: bindings_map(std::move(inputBindingsMap)) {}
	MultiplanarExternalTexture::NewBindingPoints::~NewBindingPoints() = default;

	MultiplanarExternalTexture::MultiplanarExternalTexture() = default;
	MultiplanarExternalTexture::~MultiplanarExternalTexture() = default;

	bool MultiplanarExternalTexture::ShouldRun(const Program* program, const DataMap&) const {
	for (auto* node : program->ASTNodes().Objects()) {
	if (auto* ty = node->As<ast::Type>()) {
	if (program->Sem().Get<sem::ExternalTexture>(ty)) {
	return true;
	}
	}
	}
	return false;
	}

	// Within this transform, an instance of a texture_external binding is unpacked
	// into two texture_2d<f32> bindings representing two possible planes of a
	// single texture and a uniform buffer binding representing a struct of
	// parameters. Calls to textureLoad or textureSampleLevel that contain a
	// texture_external parameter will be transformed into a newly generated version
	// of the function, which can perform the desired operation on a single RGBA
	// plane or on separate Y and UV planes.
	void MultiplanarExternalTexture::Run(CloneContext& ctx, const DataMap& inputs, DataMap&) const {
	auto* new_binding_points = inputs.Get<NewBindingPoints>();

	if (!new_binding_points) {
	ctx.dst->Diagnostics().add_error(
	diag::System::Transform,
	"missing new binding point data for " + std::string(TypeInfo().name));
	return;
	}

	State state(ctx, new_binding_points);

	state.Process();

	ctx.Clone();
	}

	} // namespace tint::transform