src/tint/transform/multiplanar_external_texture.cc - tint - 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);

 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 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;

   /// 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* var : ctx.src->AST().GlobalVariables()) {
       auto* sem_var = sem.Get(var);
       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 (var->attributes.empty()) {
         continue;
       }

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

       // 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 = {var->BindingPoint().group->value,
                          var->BindingPoint().binding->value};

       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(var->symbol);
       syms.plane_1 = b.Symbols().New("ext_tex_plane_1");
       b.Global(syms.plane_1,
                b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32()),
                b.GroupAndBinding(bps.plane_1.group, bps.plane_1.binding));
       syms.params = b.Symbols().New("ext_tex_params");
       b.Global(syms.params, b.ty.type_name("ExternalTextureParams"),
                ast::StorageClass::kUniform,
                b.GroupAndBinding(bps.params.group, bps.params.binding));

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

       auto* replacement =
           b.Var(syms.plane_0,
                 b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32()),
                 cloned_constructor, cloned_attributes);
       ctx.Replace(var, 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()) {
             createExtTexParamsStruct();
           }
           // 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* builtin = sem.Get(expr)->Target()->As<sem::Builtin>();

           if (builtin && !builtin->Parameters().empty() &&
               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 (sem.Get(expr)->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 ExternalTextureParams struct.
   void createExtTexParamsStruct() {
     ast::StructMemberList member_list = {
         b.Member("numPlanes", b.ty.u32()), b.Member("vr", b.ty.f32()),
         b.Member("ug", b.ty.f32()), b.Member("vg", b.ty.f32()),
         b.Member("ub", b.ty.f32())};

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

     b.Structure(params_struct_sym, member_list);
   }

   /// 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
   ast::StatementList createTexFnExtStatementList(sem::BuiltinType call_type) {
     using f32 = ProgramBuilder::f32;
     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", 0.0f);
       // textureSampleLevel(plane0, smp, coord.xy, 0.0);
       plane_0_call =
           b.Call("textureSampleLevel", "plane0", "smp", "coord", 0.0f);
       // textureSampleLevel(plane1, smp, coord.xy, 0.0);
       plane_1_call =
           b.Call("textureSampleLevel", "plane1", "smp", "coord", 0.0f);
     } else if (call_type == sem::BuiltinType::kTextureLoad) {
       // textureLoad(plane0, coords.xy, 0);
       single_plane_call = b.Call("textureLoad", "plane0", "coord", 0);
       // textureLoad(plane0, coords.xy, 0);
       plane_0_call = b.Call("textureLoad", "plane0", "coord", 0);
       // textureLoad(plane1, coords.xy, 0);
       plane_1_call = b.Call("textureLoad", "plane1", "coord", 0);
     } else {
       TINT_ICE(Transform, b.Diagnostics())
           << "unhandled builtin: " << call_type;
     }

     return {
         // if (params.numPlanes == 1u) {
         //    return singlePlaneCall
         // }
         b.If(b.create<ast::BinaryExpression>(
                  ast::BinaryOp::kEqual, b.MemberAccessor("params", "numPlanes"),
                  b.Expr(1u)),
              b.Block(b.Return(single_plane_call))),
         // let y = plane0Call.r - 0.0625;
         b.Decl(b.Const("y", nullptr,
                        b.Sub(b.MemberAccessor(plane_0_call, "r"), 0.0625f))),
         // let uv = plane1Call.rg - 0.5;
         b.Decl(b.Const("uv", nullptr,
                        b.Sub(b.MemberAccessor(plane_1_call, "rg"), 0.5f))),
         // let u = uv.x;
         b.Decl(b.Const("u", nullptr, b.MemberAccessor("uv", "x"))),
         // let v = uv.y;
         b.Decl(b.Const("v", nullptr, b.MemberAccessor("uv", "y"))),
         // let r = 1.164 * y + params.vr * v;
         b.Decl(b.Const("r", nullptr,
                        b.Add(b.Mul(1.164f, "y"),
                              b.Mul(b.MemberAccessor("params", "vr"), "v")))),
         // let g = 1.164 * y - params.ug * u - params.vg * v;
         b.Decl(
             b.Const("g", nullptr,
                     b.Sub(b.Sub(b.Mul(1.164f, "y"),
                                 b.Mul(b.MemberAccessor("params", "ug"), "u")),
                           b.Mul(b.MemberAccessor("params", "vg"), "v")))),
         // let b = 1.164 * y + params.ub * u;
         b.Decl(b.Const("b", nullptr,
                        b.Add(b.Mul(1.164f, "y"),
                              b.Mul(b.MemberAccessor("params", "ub"), "u")))),
         // return vec4<f32>(r, g, b, 1.0);
         b.Return(b.vec4<f32>("r", "g", "b", 1.0f)),
     };
   }

   /// 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) {
     ast::ExpressionList params;
     const ast::Expression* plane_0_binding_param = ctx.Clone(expr->args[0]);

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

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

       // Emit the textureSampleExternal function.
       ast::VariableList varList = {
           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))};

       ast::StatementList statementList =
           createTexFnExtStatementList(sem::BuiltinType::kTextureSampleLevel);

       b.Func(texture_sample_external_sym, varList, b.ty.vec4(b.ty.f32()),
              statementList, {});
     }

     const ast::IdentifierExpression* exp = b.Expr(texture_sample_external_sym);
     params = {plane_0_binding_param, b.Expr(syms.plane_1),
               ctx.Clone(expr->args[1]), ctx.Clone(expr->args[2]),
               b.Expr(syms.params)};
     return b.Call(exp, 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) {
     ast::ExpressionList params;
     const ast::Expression* plane_0_binding_param = ctx.Clone(expr->args[0]);

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

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

       // Emit the textureLoadExternal function.
       ast::VariableList var_list = {
           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))};

       ast::StatementList statement_list =
           createTexFnExtStatementList(sem::BuiltinType::kTextureLoad);

       b.Func(texture_load_external_sym, var_list, b.ty.vec4(b.ty.f32()),
              statement_list, {});
     }

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

	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 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;

	/// 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* var : ctx.src->AST().GlobalVariables()) {
	auto* sem_var = sem.Get(var);
	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 (var->attributes.empty()) {
	continue;
	}

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

	// 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 = {var->BindingPoint().group->value,
	var->BindingPoint().binding->value};

	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(var->symbol);
	syms.plane_1 = b.Symbols().New("ext_tex_plane_1");
	b.Global(syms.plane_1,
	b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32()),
	b.GroupAndBinding(bps.plane_1.group, bps.plane_1.binding));
	syms.params = b.Symbols().New("ext_tex_params");
	b.Global(syms.params, b.ty.type_name("ExternalTextureParams"),
	ast::StorageClass::kUniform,
	b.GroupAndBinding(bps.params.group, bps.params.binding));

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

	auto* replacement =
	b.Var(syms.plane_0,
	b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32()),
	cloned_constructor, cloned_attributes);
	ctx.Replace(var, 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()) {
	createExtTexParamsStruct();
	}
	// 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* builtin = sem.Get(expr)->Target()->As<sem::Builtin>();

	if (builtin && !builtin->Parameters().empty() &&
	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 (sem.Get(expr)->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 ExternalTextureParams struct.
	void createExtTexParamsStruct() {
	ast::StructMemberList member_list = {
	b.Member("numPlanes", b.ty.u32()), b.Member("vr", b.ty.f32()),
	b.Member("ug", b.ty.f32()), b.Member("vg", b.ty.f32()),
	b.Member("ub", b.ty.f32())};

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

	b.Structure(params_struct_sym, member_list);
	}

	/// 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
	ast::StatementList createTexFnExtStatementList(sem::BuiltinType call_type) {
	using f32 = ProgramBuilder::f32;
	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", 0.0f);
	// textureSampleLevel(plane0, smp, coord.xy, 0.0);
	plane_0_call =
	b.Call("textureSampleLevel", "plane0", "smp", "coord", 0.0f);
	// textureSampleLevel(plane1, smp, coord.xy, 0.0);
	plane_1_call =
	b.Call("textureSampleLevel", "plane1", "smp", "coord", 0.0f);
	} else if (call_type == sem::BuiltinType::kTextureLoad) {
	// textureLoad(plane0, coords.xy, 0);
	single_plane_call = b.Call("textureLoad", "plane0", "coord", 0);
	// textureLoad(plane0, coords.xy, 0);
	plane_0_call = b.Call("textureLoad", "plane0", "coord", 0);
	// textureLoad(plane1, coords.xy, 0);
	plane_1_call = b.Call("textureLoad", "plane1", "coord", 0);
	} else {
	TINT_ICE(Transform, b.Diagnostics())
	<< "unhandled builtin: " << call_type;
	}

	return {
	// if (params.numPlanes == 1u) {
	// return singlePlaneCall
	// }
	b.If(b.create<ast::BinaryExpression>(
	ast::BinaryOp::kEqual, b.MemberAccessor("params", "numPlanes"),
	b.Expr(1u)),
	b.Block(b.Return(single_plane_call))),
	// let y = plane0Call.r - 0.0625;
	b.Decl(b.Const("y", nullptr,
	b.Sub(b.MemberAccessor(plane_0_call, "r"), 0.0625f))),
	// let uv = plane1Call.rg - 0.5;
	b.Decl(b.Const("uv", nullptr,
	b.Sub(b.MemberAccessor(plane_1_call, "rg"), 0.5f))),
	// let u = uv.x;
	b.Decl(b.Const("u", nullptr, b.MemberAccessor("uv", "x"))),
	// let v = uv.y;
	b.Decl(b.Const("v", nullptr, b.MemberAccessor("uv", "y"))),
	// let r = 1.164 * y + params.vr * v;
	b.Decl(b.Const("r", nullptr,
	b.Add(b.Mul(1.164f, "y"),
	b.Mul(b.MemberAccessor("params", "vr"), "v")))),
	// let g = 1.164 * y - params.ug * u - params.vg * v;
	b.Decl(
	b.Const("g", nullptr,
	b.Sub(b.Sub(b.Mul(1.164f, "y"),
	b.Mul(b.MemberAccessor("params", "ug"), "u")),
	b.Mul(b.MemberAccessor("params", "vg"), "v")))),
	// let b = 1.164 * y + params.ub * u;
	b.Decl(b.Const("b", nullptr,
	b.Add(b.Mul(1.164f, "y"),
	b.Mul(b.MemberAccessor("params", "ub"), "u")))),
	// return vec4<f32>(r, g, b, 1.0);
	b.Return(b.vec4<f32>("r", "g", "b", 1.0f)),
	};
	}

	/// 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) {
	ast::ExpressionList params;
	const ast::Expression* plane_0_binding_param = ctx.Clone(expr->args[0]);

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

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

	// Emit the textureSampleExternal function.
	ast::VariableList varList = {
	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))};

	ast::StatementList statementList =
	createTexFnExtStatementList(sem::BuiltinType::kTextureSampleLevel);

	b.Func(texture_sample_external_sym, varList, b.ty.vec4(b.ty.f32()),
	statementList, {});
	}

	const ast::IdentifierExpression* exp = b.Expr(texture_sample_external_sym);
	params = {plane_0_binding_param, b.Expr(syms.plane_1),
	ctx.Clone(expr->args[1]), ctx.Clone(expr->args[2]),
	b.Expr(syms.params)};
	return b.Call(exp, 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) {
	ast::ExpressionList params;
	const ast::Expression* plane_0_binding_param = ctx.Clone(expr->args[0]);

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

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

	// Emit the textureLoadExternal function.
	ast::VariableList var_list = {
	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))};

	ast::StatementList statement_list =
	createTexFnExtStatementList(sem::BuiltinType::kTextureLoad);

	b.Func(texture_load_external_sym, var_list, b.ty.vec4(b.ty.f32()),
	statement_list, {});
	}

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