skia2/src/gpu/GrBatchFlushState.h

/*
 * Copyright 2015 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrBatchBuffer_DEFINED
#define GrBatchBuffer_DEFINED

#include "GrBufferAllocPool.h"
#include "batches/GrVertexBatch.h"

class GrResourceProvider;

/** Tracks the state across all the GrBatches in a GrDrawTarget flush. */
class GrBatchFlushState {
public:
    GrBatchFlushState(GrGpu*, GrResourceProvider*);

    ~GrBatchFlushState() { this->reset(); }

    /** Inserts an upload to be executed after all batches in the flush prepared their draws
        but before the draws are executed to the backend 3D API. */
    void addASAPUpload(GrDrawBatch::DeferredUploadFn&& upload) {
        fAsapUploads.emplace_back(std::move(upload));
    }

    const GrCaps& caps() const { return *fGpu->caps(); }
    GrResourceProvider* resourceProvider() const { return fResourceProvider; }

    /** Has the token been flushed to the backend 3D API. */
    bool hasDrawBeenFlushed(GrBatchDrawToken token) const {
        return token.fSequenceNumber <= fLastFlushedToken.fSequenceNumber;
    }

    /** Issue a token to an operation that is being enqueued. */
    GrBatchDrawToken issueDrawToken() {
        return GrBatchDrawToken(++fLastIssuedToken.fSequenceNumber);
    }

    /** Call every time a draw that was issued a token is flushed */
    void flushToken() { ++fLastFlushedToken.fSequenceNumber; }

    /** Gets the next draw token that will be issued. */
    GrBatchDrawToken nextDrawToken() const {
        return GrBatchDrawToken(fLastIssuedToken.fSequenceNumber + 1);
    }

    /** The last token flushed to all the way to the backend API. */
    GrBatchDrawToken nextTokenToFlush() const {
        return GrBatchDrawToken(fLastFlushedToken.fSequenceNumber + 1);
    }

    void* makeVertexSpace(size_t vertexSize, int vertexCount,
                          const GrBuffer** buffer, int* startVertex);
    uint16_t* makeIndexSpace(int indexCount, const GrBuffer** buffer, int* startIndex);

    /** This is called after each batch has a chance to prepare its draws and before the draws
        are issued. */
    void preIssueDraws() {
        fVertexPool.unmap();
        fIndexPool.unmap();
        int uploadCount = fAsapUploads.count();

        for (int i = 0; i < uploadCount; i++) {
            this->doUpload(fAsapUploads[i]);
        }
        fAsapUploads.reset();
    }

    void doUpload(GrDrawBatch::DeferredUploadFn& upload) {
        GrDrawBatch::WritePixelsFn wp = [this] (GrSurface* surface,
                int left, int top, int width, int height,
                GrPixelConfig config, const void* buffer,
                size_t rowBytes) -> bool {
            return this->fGpu->writePixels(surface, left, top, width, height, config, buffer,
                                           rowBytes);
        };
        GrDrawBatch::TransferPixelsFn tp = [this](GrTexture* texture,
                                                int left, int top, int width, int height,
                                                GrPixelConfig config, GrBuffer* buffer,
                                                size_t offset, size_t rowBytes) -> bool {
            return this->fGpu->transferPixels(texture, left, top, width, height, config, buffer,
                                              offset, rowBytes);
        };
        upload(wp, tp);
    }

    void putBackIndices(size_t indices) { fIndexPool.putBack(indices * sizeof(uint16_t)); }

    void putBackVertexSpace(size_t sizeInBytes) { fVertexPool.putBack(sizeInBytes); }

    GrGpu* gpu() { return fGpu; }

    void reset() {
        fVertexPool.reset();
        fIndexPool.reset();
    }

private:

    GrGpu*                                              fGpu;

    GrResourceProvider*                                 fResourceProvider;

    GrVertexBufferAllocPool                             fVertexPool;
    GrIndexBufferAllocPool                              fIndexPool;

    SkSTArray<4, GrDrawBatch::DeferredUploadFn>         fAsapUploads;

    GrBatchDrawToken                                    fLastIssuedToken;

    GrBatchDrawToken                                    fLastFlushedToken;
};

/**
 * A word about uploads and tokens: Batches should usually schedule their uploads to occur at the
 * begining of a frame whenever possible. These are called ASAP uploads. Of course, this requires
 * that there are no draws that have yet to be flushed that rely on the old texture contents. In
 * that case the ASAP upload would happen prior to the previous draw causing the draw to read the
 * new (wrong) texture data. In that case they should schedule an inline upload.
 *
 * Batches, in conjunction with helpers such as GrBatchAtlas, can use the token system to know
 * what the most recent draw was that referenced a resource (or portion of a resource). Each draw
 * is assigned a token. A resource (or portion) can be tagged with the most recent draw's
 * token. The target provides a facility for testing whether the draw corresponding to the token
 * has been flushed. If it has not been flushed then the batch must perform an inline upload
 * instead. When scheduling an inline upload the batch provides the token of the draw that the
 * upload must occur before. The upload will then occur between the draw that requires the new
 * data but after the token that requires the old data.
 *
 * TODO: Currently the token/upload interface is spread over GrDrawBatch, GrVertexBatch,
 * GrDrawBatch::Target, and GrVertexBatch::Target. However, the interface at the GrDrawBatch
 * level is not complete and isn't useful. We should push it down to GrVertexBatch until it
 * is required at the GrDrawBatch level.
 */
 
/**
 * GrDrawBatch instances use this object to allocate space for their geometry and to issue the draws
 * that render their batch.
 */
class GrDrawBatch::Target {
public:
    Target(GrBatchFlushState* state, GrDrawBatch* batch) : fState(state), fBatch(batch) {}

    /** Returns the token of the draw that this upload will occur before. */
    GrBatchDrawToken addInlineUpload(DeferredUploadFn&& upload) {
        fBatch->fInlineUploads.emplace_back(std::move(upload), fState->nextDrawToken());
        return fBatch->fInlineUploads.back().fUploadBeforeToken;
    }

    /** Returns the token of the draw that this upload will occur before. Since ASAP uploads
        are done first during a flush, this will be the first token since the most recent
        flush. */
    GrBatchDrawToken addAsapUpload(DeferredUploadFn&& upload) {
        fState->addASAPUpload(std::move(upload));
        return fState->nextTokenToFlush();
    }

    bool hasDrawBeenFlushed(GrBatchDrawToken token) const {
        return fState->hasDrawBeenFlushed(token);
    }

    /** Gets the next draw token that will be issued by this target. This can be used by a batch
        to record that the next draw it issues will use a resource (e.g. texture) while preparing
        that draw. */
    GrBatchDrawToken nextDrawToken() const { return fState->nextDrawToken(); }

    const GrCaps& caps() const { return fState->caps(); }

    GrResourceProvider* resourceProvider() const { return fState->resourceProvider(); }

protected:
    GrDrawBatch* batch() { return fBatch; }
    GrBatchFlushState* state() { return fState; }

private:
    GrBatchFlushState*  fState;
    GrDrawBatch*        fBatch;
};

/** Extension of GrDrawBatch::Target for use by GrVertexBatch. Adds the ability to create vertex
    draws. */
class GrVertexBatch::Target : public GrDrawBatch::Target {
public:
    Target(GrBatchFlushState* state, GrVertexBatch* batch) : INHERITED(state, batch) {}

    void draw(const GrGeometryProcessor* gp, const GrMesh& mesh);

    void* makeVertexSpace(size_t vertexSize, int vertexCount,
                          const GrBuffer** buffer, int* startVertex) {
        return this->state()->makeVertexSpace(vertexSize, vertexCount, buffer, startVertex);
    }

    uint16_t* makeIndexSpace(int indexCount, const GrBuffer** buffer, int* startIndex) {
        return this->state()->makeIndexSpace(indexCount, buffer, startIndex);
    }

    /** Helpers for batches which over-allocate and then return data to the pool. */
    void putBackIndices(int indices) { this->state()->putBackIndices(indices); }
    void putBackVertices(int vertices, size_t vertexStride) {
        this->state()->putBackVertexSpace(vertices * vertexStride);
    }

private:
    GrVertexBatch* vertexBatch() { return static_cast<GrVertexBatch*>(this->batch()); }
    typedef GrDrawBatch::Target INHERITED;
};

#endif