src/core/SkMesh.cpp

/*
 * Copyright 2021 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "include/core/SkMesh.h"

#ifdef SK_ENABLE_SKSL
#include "include/core/SkColorSpace.h"
#include "include/core/SkData.h"
#include "include/core/SkMath.h"
#include "include/private/SkOpts_spi.h"
#include "include/private/SkSLProgramElement.h"
#include "include/private/SkSLProgramKind.h"
#include "src/core/SkMeshPriv.h"
#include "src/core/SkSafeMath.h"
#include "src/sksl/SkSLAnalysis.h"
#include "src/sksl/SkSLBuiltinTypes.h"
#include "src/sksl/SkSLCompiler.h"
#include "src/sksl/SkSLSharedCompiler.h"
#include "src/sksl/ir/SkSLFunctionDeclaration.h"
#include "src/sksl/ir/SkSLFunctionDefinition.h"
#include "src/sksl/ir/SkSLProgram.h"
#include "src/sksl/ir/SkSLType.h"
#include "src/sksl/ir/SkSLVariable.h"

#include <locale>
#include <string>
#include <tuple>
#include <type_traits>
#include <utility>

using Attribute = SkMeshSpecification::Attribute;
using Varying   = SkMeshSpecification::Varying;

using IndexBuffer  = SkMesh::IndexBuffer;
using VertexBuffer = SkMesh::VertexBuffer;

#define RETURN_FAILURE(...) return Result{nullptr, SkStringPrintf(__VA_ARGS__)}

#define RETURN_ERROR(...) return std::make_tuple(false, SkStringPrintf(__VA_ARGS__))

#define RETURN_SUCCESS return std::make_tuple(true, SkString{})

static bool has_main(const SkSL::Program& p) {
    for (const SkSL::ProgramElement* elem : p.elements()) {
        if (elem->is<SkSL::FunctionDefinition>()) {
            const SkSL::FunctionDefinition& defn = elem->as<SkSL::FunctionDefinition>();
            const SkSL::FunctionDeclaration& decl = defn.declaration();
            if (decl.isMain()) {
                return true;
            }
        }
    }
    return false;
}

using ColorType = SkMeshSpecificationPriv::ColorType;

static std::tuple<ColorType, bool>
get_fs_color_type_and_local_coords(const SkSL::Program& fsProgram) {
    for (const SkSL::ProgramElement* elem : fsProgram.elements()) {
        if (elem->is<SkSL::FunctionDefinition>()) {
            const SkSL::FunctionDefinition& defn = elem->as<SkSL::FunctionDefinition>();
            const SkSL::FunctionDeclaration& decl = defn.declaration();
            if (decl.isMain()) {

                SkMeshSpecificationPriv::ColorType ct;
                SkASSERT(decl.parameters().size() == 1 || decl.parameters().size() == 2);
                if (decl.parameters().size() == 1) {
                    ct = ColorType::kNone;
                } else {
                    const SkSL::Type& paramType = decl.parameters()[1]->type();
                    SkASSERT(paramType.matches(*fsProgram.fContext->fTypes.fHalf4) ||
                             paramType.matches(*fsProgram.fContext->fTypes.fFloat4));
                    ct = paramType.matches(*fsProgram.fContext->fTypes.fHalf4)
                                 ? ColorType::kHalf4
                                 : ColorType::kFloat4;
                }

                const SkSL::Type& returnType = decl.returnType();
                SkASSERT(returnType.matches(*fsProgram.fContext->fTypes.fVoid) ||
                         returnType.matches(*fsProgram.fContext->fTypes.fFloat2));
                bool hasLocalCoords = returnType.matches(*fsProgram.fContext->fTypes.fFloat2);

                return std::make_tuple(ct, hasLocalCoords);
            }
        }
    }
    SkUNREACHABLE;
}

// This is a non-exhaustive check for the validity of a variable name. The SkSL compiler will
// actually process the name. We're just guarding against having multiple tokens embedded in the
// name before we put it into a struct definition.
static bool check_name(const SkString& name) {
    if (name.isEmpty()) {
        return false;
    }
    for (size_t i = 0; i < name.size(); ++i) {
        if (name[i] != '_' && !std::isalnum(name[i], std::locale::classic())) {
            return false;
        }
    }
    return true;
}

static size_t attribute_type_size(Attribute::Type type) {
    switch (type) {
        case Attribute::Type::kFloat:         return 4;
        case Attribute::Type::kFloat2:        return 2*4;
        case Attribute::Type::kFloat3:        return 3*4;
        case Attribute::Type::kFloat4:        return 4*4;
        case Attribute::Type::kUByte4_unorm:  return 4;
    }
    SkUNREACHABLE;
};

static const char* attribute_type_string(Attribute::Type type) {
    switch (type) {
        case Attribute::Type::kFloat:         return "float";
        case Attribute::Type::kFloat2:        return "float2";
        case Attribute::Type::kFloat3:        return "float3";
        case Attribute::Type::kFloat4:        return "float4";
        case Attribute::Type::kUByte4_unorm:  return "half4";
    }
    SkUNREACHABLE;
};

static const char* varying_type_string(Varying::Type type) {
    switch (type) {
        case Varying::Type::kFloat:  return "float";
        case Varying::Type::kFloat2: return "float2";
        case Varying::Type::kFloat3: return "float3";
        case Varying::Type::kFloat4: return "float4";
        case Varying::Type::kHalf:   return "half";
        case Varying::Type::kHalf2:  return "half2";
        case Varying::Type::kHalf3:  return "half3";
        case Varying::Type::kHalf4:  return "half4";
    }
    SkUNREACHABLE;
};

std::tuple<bool, SkString>
check_vertex_offsets_and_stride(SkSpan<const Attribute> attributes,
                                size_t                  stride) {
    // Vulkan 1.0 has a minimum maximum attribute count of 2048.
    static_assert(SkMeshSpecification::kMaxStride       <= 2048);
    // ES 2 has a max of 8.
    static_assert(SkMeshSpecification::kMaxAttributes   <= 8);
    // Four bytes alignment is required by Metal.
    static_assert(SkMeshSpecification::kStrideAlignment >= 4);
    static_assert(SkMeshSpecification::kOffsetAlignment >= 4);
    // ES2 has a minimum maximum of 8. We may need one for a broken gl_FragCoord workaround and
    // one for local coords.
    static_assert(SkMeshSpecification::kMaxVaryings     <= 6);

    if (attributes.empty()) {
        RETURN_ERROR("At least 1 attribute is required.");
    }
    if (attributes.size() > SkMeshSpecification::kMaxAttributes) {
        RETURN_ERROR("A maximum of %zu attributes is allowed.",
                     SkMeshSpecification::kMaxAttributes);
    }
    static_assert(SkIsPow2(SkMeshSpecification::kStrideAlignment));
    if (stride == 0 || stride & (SkMeshSpecification::kStrideAlignment - 1)) {
        RETURN_ERROR("Vertex stride must be a non-zero multiple of %zu.",
                     SkMeshSpecification::kStrideAlignment);
    }
    if (stride > SkMeshSpecification::kMaxStride) {
        RETURN_ERROR("Stride cannot exceed %zu.", SkMeshSpecification::kMaxStride);
    }
    for (const auto& a : attributes) {
        if (a.offset & (SkMeshSpecification::kOffsetAlignment - 1)) {
            RETURN_ERROR("Attribute offset must be a multiple of %zu.",
                         SkMeshSpecification::kOffsetAlignment);
        }
        // This equivalent to vertexAttributeAccessBeyondStride==VK_FALSE in
        // VK_KHR_portability_subset. First check is to avoid overflow in second check.
        if (a.offset >= stride || a.offset + attribute_type_size(a.type) > stride) {
            RETURN_ERROR("Attribute offset plus size cannot exceed stride.");
        }
    }
    RETURN_SUCCESS;
}

SkMeshSpecification::Result SkMeshSpecification::Make(SkSpan<const Attribute> attributes,
                                                      size_t vertexStride,
                                                      SkSpan<const Varying> varyings,
                                                      const SkString& vs,
                                                      const SkString& fs) {
    return Make(attributes,
                vertexStride,
                varyings,
                vs,
                fs,
                SkColorSpace::MakeSRGB(),
                kPremul_SkAlphaType);
}

SkMeshSpecification::Result SkMeshSpecification::Make(SkSpan<const Attribute> attributes,
                                                      size_t vertexStride,
                                                      SkSpan<const Varying> varyings,
                                                      const SkString& vs,
                                                      const SkString& fs,
                                                      sk_sp<SkColorSpace> cs) {
    return Make(attributes, vertexStride, varyings, vs, fs, std::move(cs), kPremul_SkAlphaType);
}

SkMeshSpecification::Result SkMeshSpecification::Make(SkSpan<const Attribute> attributes,
                                                      size_t vertexStride,
                                                      SkSpan<const Varying> varyings,
                                                      const SkString& vs,
                                                      const SkString& fs,
                                                      sk_sp<SkColorSpace> cs,
                                                      SkAlphaType at) {
    SkString attributesStruct("struct Attributes {\n");
    for (const auto& a : attributes) {
        attributesStruct.appendf("  %s %s;\n", attribute_type_string(a.type), a.name.c_str());
    }
    attributesStruct.append("};\n");

    SkString varyingStruct("struct Varyings {\n");
    for (const auto& v : varyings) {
        varyingStruct.appendf("  %s %s;\n", varying_type_string(v.type), v.name.c_str());
    }
    // Throw in an unused variable to avoid an empty struct, which is illegal.
    if (varyings.empty()) {
        varyingStruct.append("  bool _empty_;\n");
    }
    varyingStruct.append("};\n");

    SkString fullVS;
    fullVS.append(varyingStruct.c_str());
    fullVS.append(attributesStruct.c_str());
    fullVS.append(vs.c_str());

    SkString fullFS;
    fullFS.append(varyingStruct.c_str());
    fullFS.append(fs.c_str());

    return MakeFromSourceWithStructs(attributes,
                                     vertexStride,
                                     varyings,
                                     fullVS,
                                     fullFS,
                                     std::move(cs),
                                     at);
}

SkMeshSpecification::Result SkMeshSpecification::MakeFromSourceWithStructs(
        SkSpan<const Attribute> attributes,
        size_t                  stride,
        SkSpan<const Varying>   varyings,
        const SkString&         vs,
        const SkString&         fs,
        sk_sp<SkColorSpace>     cs,
        SkAlphaType             at) {
    if (auto [ok, error] = check_vertex_offsets_and_stride(attributes, stride); !ok) {
        return {nullptr, error};
    }

    for (const auto& a : attributes) {
        if (!check_name(a.name)) {
            RETURN_FAILURE("\"%s\" is not a valid attribute name.", a.name.c_str());
        }
    }

    if (varyings.size() > kMaxVaryings) {
        RETURN_FAILURE("A maximum of %zu varyings is allowed.", kMaxVaryings);
    }

    for (const auto& v : varyings) {
        if (!check_name(v.name)) {
            return {nullptr, SkStringPrintf("\"%s\" is not a valid varying name.", v.name.c_str())};
        }
    }

    SkSL::SharedCompiler compiler;
    SkSL::Program::Settings settings;
    settings.fEnforceES2Restrictions = true;
    std::unique_ptr<SkSL::Program> vsProgram = compiler->convertProgram(
            SkSL::ProgramKind::kMeshVertex,
            std::string(vs.c_str()),
            settings);
    if (!vsProgram) {
        RETURN_FAILURE("VS: %s", compiler->errorText().c_str());
    }
    if (!has_main(*vsProgram)) {
        RETURN_FAILURE("Vertex shader must have main function.");
    }
    if (SkSL::Analysis::CallsColorTransformIntrinsics(*vsProgram)) {
        RETURN_FAILURE("Color transform intrinsics are not permitted in custom mesh shaders");
    }

    std::unique_ptr<SkSL::Program> fsProgram = compiler->convertProgram(
            SkSL::ProgramKind::kMeshFragment,
            std::string(fs.c_str()),
            settings);

    if (!fsProgram) {
        RETURN_FAILURE("FS: %s", compiler->errorText().c_str());
    }
    if (!has_main(*fsProgram)) {
        RETURN_FAILURE("Fragment shader must have main function.");
    }
    if (SkSL::Analysis::CallsColorTransformIntrinsics(*fsProgram)) {
        RETURN_FAILURE("Color transform intrinsics are not permitted in custom mesh shaders");
    }

    auto [ct, hasLocalCoords] = get_fs_color_type_and_local_coords(*fsProgram);

    if (ct == ColorType::kNone) {
        cs = nullptr;
        at = kPremul_SkAlphaType;
    } else {
        if (!cs) {
            return {nullptr, SkString{"Must provide a color space if FS returns a color."}};
        }
        if (at == kUnknown_SkAlphaType) {
            return {nullptr, SkString{"Must provide a valid alpha type if FS returns a color."}};
        }
    }

    return {sk_sp<SkMeshSpecification>(new SkMeshSpecification(attributes,
                                                               stride,
                                                               varyings,
                                                               std::move(vsProgram),
                                                               std::move(fsProgram),
                                                               ct,
                                                               hasLocalCoords,
                                                               std::move(cs),
                                                               at)),
            /*error=*/{}};
}

SkMeshSpecification::~SkMeshSpecification() = default;

SkMeshSpecification::SkMeshSpecification(SkSpan<const Attribute>        attributes,
                                         size_t                         stride,
                                         SkSpan<const Varying>          varyings,
                                         std::unique_ptr<SkSL::Program> vs,
                                         std::unique_ptr<SkSL::Program> fs,
                                         ColorType                      ct,
                                         bool                           hasLocalCoords,
                                         sk_sp<SkColorSpace>            cs,
                                         SkAlphaType                    at)
        : fAttributes(attributes.begin(), attributes.end())
        , fVaryings(varyings.begin(), varyings.end())
        , fVS(std::move(vs))
        , fFS(std::move(fs))
        , fStride(stride)
        , fColorType(ct)
        , fHasLocalCoords(hasLocalCoords)
        , fColorSpace(std::move(cs))
        , fAlphaType(at) {
    fHash = SkOpts::hash_fn(fVS->fSource->c_str(), fVS->fSource->size(), 0);
    fHash = SkOpts::hash_fn(fFS->fSource->c_str(), fFS->fSource->size(), fHash);

    // The attributes and varyings SkSL struct declarations are included in the program source.
    // However, the attribute offsets and types need to be included, the latter because the SkSL
    // struct definition has the GPU type but not the CPU data format.
    for (const auto& a : fAttributes) {
        fHash = SkOpts::hash_fn(&a.offset, sizeof(a.offset), fHash);
        fHash = SkOpts::hash_fn(&a.type,   sizeof(a.type),   fHash);
    }

    fHash = SkOpts::hash_fn(&stride, sizeof(stride), fHash);

    uint64_t csHash = fColorSpace ? fColorSpace->hash() : 0;
    fHash = SkOpts::hash_fn(&csHash, sizeof(csHash), fHash);

    auto atInt = static_cast<uint32_t>(fAlphaType);
    fHash = SkOpts::hash_fn(&atInt, sizeof(atInt), fHash);
}

SkMesh::SkMesh()  = default;
SkMesh::~SkMesh() = default;

SkMesh::SkMesh(const SkMesh&) = default;
SkMesh::SkMesh(SkMesh&&)      = default;

SkMesh& SkMesh::operator=(const SkMesh&) = default;
SkMesh& SkMesh::operator=(SkMesh&&)      = default;

sk_sp<IndexBuffer> SkMesh::MakeIndexBuffer(GrDirectContext* dc, sk_sp<const SkData> data) {
    if (!data) {
        return nullptr;
    }
    if (!dc) {
        return SkMeshPriv::CpuIndexBuffer::Make(std::move(data));
    }
#if SK_SUPPORT_GPU
    return SkMeshPriv::GpuIndexBuffer::Make(dc, std::move(data));
#endif
    return nullptr;
}

sk_sp<VertexBuffer> SkMesh::MakeVertexBuffer(GrDirectContext* dc, sk_sp<const SkData> data) {
    if (!data) {
        return nullptr;
    }
    if (!dc) {
        return SkMeshPriv::CpuVertexBuffer::Make(std::move(data));
    }
#if SK_SUPPORT_GPU
    return SkMeshPriv::GpuVertexBuffer::Make(dc, std::move(data));
#endif
    return nullptr;
}

SkMesh SkMesh::Make(sk_sp<SkMeshSpecification> spec,
                    Mode mode,
                    sk_sp<VertexBuffer> vb,
                    size_t vertexCount,
                    size_t vertexOffset,
                    const SkRect& bounds) {
    SkMesh cm;
    cm.fSpec    = std::move(spec);
    cm.fMode    = mode;
    cm.fVB      = std::move(vb);
    cm.fVCount  = vertexCount;
    cm.fVOffset = vertexOffset;
    cm.fBounds  = bounds;
    return cm.validate() ? cm : SkMesh{};
}

SkMesh SkMesh::MakeIndexed(sk_sp<SkMeshSpecification> spec,
                           Mode mode,
                           sk_sp<VertexBuffer> vb,
                           size_t vertexCount,
                           size_t vertexOffset,
                           sk_sp<IndexBuffer> ib,
                           size_t indexCount,
                           size_t indexOffset,
                           const SkRect& bounds) {
    SkMesh cm;
    cm.fSpec    = std::move(spec);
    cm.fMode    = mode;
    cm.fVB      = std::move(vb);
    cm.fVCount  = vertexCount;
    cm.fVOffset = vertexOffset;
    cm.fIB      = std::move(ib);
    cm.fICount  = indexCount;
    cm.fIOffset = indexOffset;
    cm.fBounds  = bounds;
    return cm.validate() ? cm : SkMesh{};
}

bool SkMesh::isValid() const {
    bool valid = SkToBool(fSpec);
    SkASSERT(valid == this->validate());
    return valid;
}

static size_t min_vcount_for_mode(SkMesh::Mode mode) {
    switch (mode) {
        case SkMesh::Mode::kTriangles:     return 3;
        case SkMesh::Mode::kTriangleStrip: return 3;
    }
    SkUNREACHABLE;
}

bool SkMesh::validate() const {
    if (!fSpec) {
        return false;
    }

    if (!fVB) {
        return false;
    }

    if (!fVCount) {
        return false;
    }

    auto vb = static_cast<SkMeshPriv::VB*>(fVB.get());
    auto ib = static_cast<SkMeshPriv::IB*>(fIB.get());

    SkSafeMath sm;
    size_t vsize = sm.mul(fSpec->stride(), fVCount);
    if (sm.add(vsize, fVOffset) > vb->size()) {
        return false;
    }

    if (fVOffset%fSpec->stride() != 0) {
        return false;
    }

    if (ib) {
        if (fICount < min_vcount_for_mode(fMode)) {
            return false;
        }
        size_t isize = sm.mul(sizeof(uint16_t), fICount);
        if (sm.add(isize, fIOffset) > ib->size()) {
            return false;
        }
        // If we allow 32 bit indices then this should enforce 4 byte alignment in that case.
        if (!SkIsAlign2(fIOffset)) {
            return false;
        }
    } else {
        if (fVCount < min_vcount_for_mode(fMode)) {
            return false;
        }
        if (fICount || fIOffset) {
            return false;
        }
    }

    return sm.ok();
}

#endif  // SK_ENABLE_SKSL