GhostEngine/Ghost.DSL/ShaderCompiler/Parser/PassBlock.cs

using Ghost.Core.Graphics;

namespace Ghost.DSL.ShaderCompiler.Parser;

// TODO: Add pass template support.
//   Pass templates let user to inject their own custom code into the generated HLSL code.
//   This is useful for adding custom lighting models, custom shadowing techniques, or other advanced effects without touching the core shader code.
internal class PassBlock : IBlockParser<PassSyntax, PassSemantic>
{
    public static bool ShouldEnter(Token token)
    {
        return token.Match(TokenType.Keyword, TokenLexicon.KnownKeywords.PASS);
    }

    public static PassSyntax Parse(TokenStreamSlice stream)
    {
        var pass = new PassSyntax();

        stream.Expect(TokenType.Keyword);
        pass.name = stream.Expect(TokenType.StringLiteral);
        stream.Expect(TokenType.LBrace);

        var bodyStream = stream.Slice(stream.Remaining - 1);
        while (bodyStream.TryPeek(out var nextToken))
        {
            if (DefinesBlock.ShouldEnter(nextToken))
            {
                pass.defines = DefinesBlock.Parse(bodyStream.SliceNextBlock());
            }
            else if (KeywordsBlock.ShouldEnter(nextToken))
            {
                pass.keywords = KeywordsBlock.Parse(bodyStream.SliceNextBlock());
            }
            else if (PipelineBlock.ShouldEnter(nextToken))
            {
                pass.localPipeline = PipelineBlock.Parse(bodyStream.SliceNextBlock());
            }
            else if (IncludesBlock.ShouldEnter(nextToken))
            {
                pass.includes = IncludesBlock.Parse(bodyStream.SliceNextBlock());
            }
            else if (nextToken.Match(TokenType.Identifier))
            {
                var func = ParseUtility.ParseFunction(ref bodyStream, TokenType.StringLiteral);

                pass.functionCalls ??= new();
                pass.functionCalls.Add(func);
            }
            else
            {
                throw new Exception($"Unexpected token '{nextToken}' in pass body.");
            }
        }

        stream.Expect(TokenType.RBrace);

        return pass;
    }

    public static PassSemantic? SemanticAnalysis(PassSyntax? syntax, List<DSLShaderError> errors)
    {
        if (syntax == null)
        {
            return null;
        }

        var semantic = new PassSemantic
        {
            name = syntax.name.lexeme,
            defines = DefinesBlock.SemanticAnalysis(syntax.defines, errors),
            keywords = KeywordsBlock.SemanticAnalysis(syntax.keywords, errors),
            localPipeline = PipelineBlock.SemanticAnalysis(syntax.localPipeline, errors),
        };

        if (syntax.functionCalls != null)
        {
            foreach (var func in syntax.functionCalls)
            {
                switch (func.name.lexeme)
                {
                    case TokenLexicon.KnownFunctions.TASK_SHADER:
                        AnalysisShaderEntry(errors, func, ref semantic.taskShader);
                        break;

                    case TokenLexicon.KnownFunctions.MESH_SHADER:
                        AnalysisShaderEntry(errors, func, ref semantic.meshShader);
                        break;

                    case TokenLexicon.KnownFunctions.PIXEL_SHADER:
                        AnalysisShaderEntry(errors, func, ref semantic.pixelShader);
                        break;

                    default:
                        errors.Add(new DSLShaderError
                        {
                            message = $"Unknown function '{func.name.lexeme}' in pass {syntax.name.lexeme}.",
                            line = func.name.line,
                            column = func.name.column
                        });
                        break;
                }
            }
        }

        if (semantic.meshShader.shader == null || semantic.pixelShader.shader == null)
        {
            // TODO: Inheritance from base pass.
            // TODO: Add mesh shader support.
            errors.Add(new DSLShaderError
            {
                message = $"Pass {syntax.name.lexeme} must contain a mesh shader (ms) and a pixel shader (ps) declaration.",
                line = syntax.name.line,
                column = syntax.name.column
            });
        }

        return semantic;
    }

    private static void AnalysisShaderEntry(List<DSLShaderError> errors, FunctionCallDeclaration func, ref ShaderEntryPoint shaderEntryPoint)
    {
        if (func.arguments?.Count != 2)
        {
            errors.Add(new DSLShaderError
            {
                message = "Shader declaration requires exactly two arguments: (shaderPath, entryPoint).",
                line = func.name.line,
                column = func.name.column
            });
        }
        else
        {
            shaderEntryPoint = new ShaderEntryPoint
            {
                shader = func.arguments[0].lexeme,
                entry = func.arguments[1].lexeme
            };
        }
    }
}