//
// Copyright (c) 2020 The ANGLE Project Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// mtl_occlusion_query_pool: A visibility pool for allocating visibility query within
// one render pass.
//

#include "libANGLE/renderer/metal/mtl_occlusion_query_pool.h"

#include "libANGLE/renderer/metal/ContextMtl.h"
#include "libANGLE/renderer/metal/DisplayMtl.h"
#include "libANGLE/renderer/metal/QueryMtl.h"

namespace rx
{
namespace mtl
{

// OcclusionQueryPool implementation
OcclusionQueryPool::OcclusionQueryPool() {}
OcclusionQueryPool::~OcclusionQueryPool() {}

void OcclusionQueryPool::destroy(ContextMtl *contextMtl)
{
    mRenderPassResultsPool = nullptr;
    for (QueryMtl *allocatedQuery : mAllocatedQueries)
    {
        if (!allocatedQuery)
        {
            continue;
        }
        allocatedQuery->clearAllocatedVisibilityOffsets();
    }
    mAllocatedQueries.clear();
}

angle::Result OcclusionQueryPool::allocateQueryOffset(ContextMtl *contextMtl,
                                                      QueryMtl *query,
                                                      bool clearOldValue)
{
    // Only query that already has allocated offset or first query of the render pass is allowed to
    // keep old value. Other queries must be reset to zero before counting the samples visibility in
    // draw calls.
    ASSERT(clearOldValue || mAllocatedQueries.empty() ||
           !query->getAllocatedVisibilityOffsets().empty());

    uint32_t currentOffset =
        static_cast<uint32_t>(mAllocatedQueries.size()) * kOcclusionQueryResultSize;
    if (!mRenderPassResultsPool)
    {
        ASSERT(!mUsed);
        // First allocation
        ANGLE_TRY(Buffer::MakeBufferWithStorageMode(
            contextMtl, MTLStorageModePrivate, kOcclusionQueryResultSize, &mRenderPassResultsPool));
        mRenderPassResultsPool->get().label = @"OcclusionQueryPool";
    }
    else if (currentOffset + kOcclusionQueryResultSize > mRenderPassResultsPool->size())
    {
        // Double the capacity
        ANGLE_TRY(Buffer::MakeBufferWithStorageMode(contextMtl, MTLStorageModePrivate,
                                                    mRenderPassResultsPool->size() * 2,
                                                    &mRenderPassResultsPool));
        mUsed                               = false;
        mRenderPassResultsPool->get().label = @"OcclusionQueryPool";
    }

    if (clearOldValue)
    {
        // If old value is not needed, deallocate any offset previously allocated for this query.
        deallocateQueryOffset(contextMtl, query);
    }
    if (query->getAllocatedVisibilityOffsets().empty())
    {
        mAllocatedQueries.push_back(query);
        query->setFirstAllocatedVisibilityOffset(currentOffset);
    }
    else
    {
        // Additional offset allocated for a query is only allowed if it is a continuous region.
        ASSERT(currentOffset ==
               query->getAllocatedVisibilityOffsets().back() + kOcclusionQueryResultSize);
        // Just reserve an empty slot in the allocated query array
        mAllocatedQueries.push_back(nullptr);
        query->addAllocatedVisibilityOffset();
    }

    if (currentOffset == 0)
    {
        mResetFirstQuery = clearOldValue;
        if (!clearOldValue && !contextMtl->getDisplay()->getFeatures().allowBufferReadWrite.enabled)
        {
            // If old value of first query needs to be retained and device doesn't support buffer
            // read-write, we need an additional offset to store the old value of the query.
            return allocateQueryOffset(contextMtl, query, false);
        }
    }

    return angle::Result::Continue;
}

void OcclusionQueryPool::deallocateQueryOffset(ContextMtl *contextMtl, QueryMtl *query)
{
    if (query->getAllocatedVisibilityOffsets().empty())
    {
        return;
    }

    mAllocatedQueries[query->getAllocatedVisibilityOffsets().front() / kOcclusionQueryResultSize] =
        nullptr;
    query->clearAllocatedVisibilityOffsets();
}

void OcclusionQueryPool::resolveVisibilityResults(ContextMtl *contextMtl)
{
    if (mAllocatedQueries.empty())
    {
        return;
    }

    RenderUtils &utils              = contextMtl->getDisplay()->getUtils();
    BlitCommandEncoder *blitEncoder = nullptr;
    // Combine the values stored in the offsets allocated for first query
    if (mAllocatedQueries[0])
    {
        const BufferRef &dstBuf = mAllocatedQueries[0]->getVisibilityResultBuffer();
        const VisibilityBufferOffsetsMtl &allocatedOffsets =
            mAllocatedQueries[0]->getAllocatedVisibilityOffsets();
        if (!mResetFirstQuery &&
            !contextMtl->getDisplay()->getFeatures().allowBufferReadWrite.enabled)
        {
            // If we cannot read and write to the same buffer in shader. We need to copy the old
            // value of first query to first offset allocated for it.
            blitEncoder = contextMtl->getBlitCommandEncoder();
            blitEncoder->copyBuffer(dstBuf, 0, mRenderPassResultsPool, allocatedOffsets.front(),
                                    kOcclusionQueryResultSize);
            utils.combineVisibilityResult(contextMtl, false, allocatedOffsets,
                                          mRenderPassResultsPool, dstBuf);
        }
        else
        {
            utils.combineVisibilityResult(contextMtl, !mResetFirstQuery, allocatedOffsets,
                                          mRenderPassResultsPool, dstBuf);
        }
    }

    // Combine the values stored in the offsets allocated for each of the remaining queries
    for (size_t i = 1; i < mAllocatedQueries.size(); ++i)
    {
        QueryMtl *query = mAllocatedQueries[i];
        if (!query)
        {
            continue;
        }

        const BufferRef &dstBuf = mAllocatedQueries[i]->getVisibilityResultBuffer();
        const VisibilityBufferOffsetsMtl &allocatedOffsets =
            mAllocatedQueries[i]->getAllocatedVisibilityOffsets();
        utils.combineVisibilityResult(contextMtl, false, allocatedOffsets, mRenderPassResultsPool,
                                      dstBuf);
    }

    // Request synchronization and cleanup
    blitEncoder = contextMtl->getBlitCommandEncoder();
    for (size_t i = 0; i < mAllocatedQueries.size(); ++i)
    {
        QueryMtl *query = mAllocatedQueries[i];
        if (!query)
        {
            continue;
        }

        const BufferRef &dstBuf = mAllocatedQueries[i]->getVisibilityResultBuffer();

        dstBuf->syncContent(contextMtl, blitEncoder);

        query->clearAllocatedVisibilityOffsets();
    }

    mAllocatedQueries.clear();
}

void OcclusionQueryPool::prepareRenderPassVisibilityPoolBuffer(ContextMtl *contextMtl)
{
    if (mAllocatedQueries.empty())
    {
        return;
    }

    // If the current visibility pool buffer was not used before,
    // ensure that it will be cleared next time.
    if (!mUsed)
    {
        mUsed = true;
        return;
    }

    mUsed = false;

    // If the current visibility pool buffer was used before,
    // ensure that it does not contain previous results.
    auto blitEncoder = contextMtl->getBlitCommandEncoderWithoutEndingRenderEncoder();
    blitEncoder->fillBuffer(mRenderPassResultsPool,
                            NSMakeRange(0, mAllocatedQueries.size() * kOcclusionQueryResultSize),
                            0);
    blitEncoder->endEncoding();
}

}  // namespace mtl
}  // namespace rx
