ShaderSource.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "Containers/AnsiString.h"
#include "Containers/Array.h"
#include "Containers/StringView.h"
#include "Containers/UnrealString.h"
#include "Misc/StringBuilder.h"
 
#define SHADER_SOURCE_ANSI 1 UE_DEPRECATED_MACRO(5.6, "SHADER_SOURCE_ANSI has been deprecated and should be assumed to always be 1")
#define SHADER_SOURCE_LITERAL(S) S UE_DEPRECATED_MACRO(5.6, "SHADER_SOURCE_LITERAL has been deprecated and should be replaced with just plain string literal")
#define SHADER_SOURCE_VIEWLITERAL(S) ANSITEXTVIEW(S) UE_DEPRECATED_MACRO(5.6, "SHADER_SOURCE_VIEWLITERAL has been deprecated and should be replaced with ANSITEXTVIEW")
 
/* Class used in shader compilation pipelines which wraps source code and ensures sufficient padding such that 16-byte wide SIMD
 * operations on the source are guaranteed to read valid memory even if starting from the last character.
 */
class FShaderSource
{
private:
    inline void SetLen(int32 Num, EAllowShrinking AllowShrinking = EAllowShrinking::Default)
    {
        Source.SetNumUninitialized(Num + ShaderSourceSimdPadding, AllowShrinking);
        FMemory::Memzero(Source.GetData() + Num, sizeof(CharType) * ShaderSourceSimdPadding);
 
        SourceCompressed.Empty();
        DecompressedCharCount = 0;
    }
 
public:
    typedef ANSICHAR CharType;
    typedef FAnsiStringView FViewType;
    typedef FAnsiString FStringType;
    typedef FCStringAnsi FCStringType;
 
    template <int NumChars>
    using TStringBuilder = TAnsiStringBuilder<NumChars>;
 
    UE_DEPRECATED(5.6, "Shader code is always assumed to be ANSI")
    static constexpr bool IsWide() { return false; }
    UE_DEPRECATED(5.6, "Shader code is always assumed to be ANSI, so GetSimdCharCount() is always 16")
    static constexpr int32 GetSimdCharCount() { return 16; }
    UE_DEPRECATED(5.6, "Shader code is always assumed to be ANSI, so GetSingleCharMask() is always 1")
    static constexpr int32 GetSingleCharMask() { return 1; }
 
    /* Construct an empty shader source object; will still contain padding */
    FShaderSource() { SetLen(0); };
 
    /* Given a string view construct a shader source object containing the contents of that string.
     * Note that this will incur a memcpy of the string contents.
     * @param InSrc The source string to be copied
     * @param AdditionalSlack optional additional space to allocate; this is on top of the automatic padding.
     */
    RENDERCORE_API explicit FShaderSource(FViewType InSrc, int32 AdditionalSlack = 0);
 
    /* Set the given string as the contents of this shader source object. The inner allocation will grow to fit
     * the string contents as needed.
     * Note that this will incur a memcpy of the string contents.
     * @param InSrc The source string to be copied
     * @param AdditionalSlack optional additional space to allocate; this is on top of the automatic padding.
     */
    RENDERCORE_API void Set(FViewType InSrc, int32 AdditionalSlack = 0);
 
    /* Move assignment operator accepting a string object. This will append padding bytes to the existing string, as such it's
     * best if there's sufficient extra capacity in the string storage to avoid incurring a realloc-and-copy here.
     * @param InSrc The source string whose data this object will take ownership of.
     */
    RENDERCORE_API FShaderSource& operator=(FStringType&& InSrc);
 
    /* Reduces the set size of the stored string length, optionally shrinking the allocation.
     * @param Num the desired allocation size (padding bytes will be added on top of this)
     * @param AllowShrinking whether to reallocate or keep the existing larger size allocation
     */
    inline void ShrinkToLen(int32 Num, EAllowShrinking AllowShrinking = EAllowShrinking::Default)
    {
        checkf(Num <= Len(), TEXT("Trying to shrink to %d characters but existing allocation is smaller (%d characters)"), Num, Len());
        SetLen(Num, AllowShrinking);
    }
    UE_ALLOWSHRINKING_BOOL_DEPRECATED("ShrinkToLen")
    inline void ShrinkToLen(int32 Num, bool bShrink)
    {
        ShrinkToLen(Num, bShrink ? EAllowShrinking::Yes : EAllowShrinking::No);
    }
 
    /* String view accessor. Will decompress data if it was previously compressed.
     * @return a string view pointing to the source contents, excluding padding.
     */
    inline FViewType GetView() const
    { 
        checkf(!IsCompressed(), TEXT("FShaderSource is compressed; must decompress prior to calling GetView"));
        return { Source.GetData(), Len() }; 
    }
 
    /* Direct data pointer accessor. Will decompress data if it was previously compressed.
     * @return a pointer to the source data; will be null terminated by the SIMD padding.
     */
    inline CharType* GetData()
    {
        checkf(!IsCompressed(), TEXT("FShaderSource is compressed; must decompress prior to calling GetData"));
        return Source.GetData();
    }
 
    /* IsEmpty predicate
     * @return true if this source object is empty excluding the SIMD padding, false otherwise.
     */
    inline bool IsEmpty() const { return Len() == 0; }
 
    /* Length accessor.
     * @return the non-padded length of the source (also excluding null terminator)
     */
    inline int32 Len() const
    { 
        checkf(!IsCompressed(), TEXT("Len should not be called on compressed FShaderSource."))
        return Source.Num() - ShaderSourceSimdPadding;
    };
 
    inline bool IsCompressed() const
    {
        return DecompressedCharCount != 0; // DecompressedCharCount member is only set when compression occurs
    }
 
    inline int32 GetDecompressedSize() const
    {
        return DecompressedCharCount * sizeof(FShaderSource::CharType);
    }
 
    /* FArchive serialization operator. Note this currently serializes padding for simplicity's sake.
     * @param Ar The archive to serialize from/to
     * @param ShaderSource the source object to serialize
     */
    friend FArchive& operator<<(FArchive& Ar, FShaderSource& ShaderSource);
 
    RENDERCORE_API void Compress();
    RENDERCORE_API void Decompress();
    
private:
    static_assert(sizeof(CharType) == 1);
    static constexpr int32 ShaderSourceSimdPadding = 15;
    TArray<CharType> Source;
    TArray<uint8> SourceCompressed;
    int32 DecompressedCharCount = 0;
};