chromium/third_party/skia/src/gpu/graphite/DrawWriter.h

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

#ifndef skgpu_graphite_DrawWriter_DEFINED
#define skgpu_graphite_DrawWriter_DEFINED

#include "src/base/SkAutoMalloc.h"
#include "src/gpu/BufferWriter.h"
#include "src/gpu/graphite/BufferManager.h"
#include "src/gpu/graphite/DrawTypes.h"

namespace skgpu::graphite {

namespace DrawPassCommands {
class List;
}

/**
 * DrawWriter is a helper around recording draws (to a temporary buffer or directly to a
 * CommandBuffer), particularly when the number of draws is not known ahead of time, or the vertex
 * and instance data is computed at record time and does not have a known size.
 *
 * To use, construct the DrawWriter with the current pipeline layout or call newPipelineState() on
 * an existing DrawWriter and then bind that matching pipeline. When other dynamic state needs to
 * change between draw calls, notify the DrawWriter using newDynamicState() before recording the
 * modifications. See the listing below for how to append dynamic data or draw with existing buffers
 *
 * CommandBuffer::draw(vertices)
 *  - dynamic vertex data     -> DrawWriter::Vertices(writer) verts;
 *                               verts.append(n) << ...;
 *  - fixed vertex data       -> writer.draw(vertices, {}, vertexCount)
 *
 * CommandBuffer::drawIndexed(vertices, indices)
 *  - dynamic vertex data     -> unsupported
 *  - fixed vertex,index data -> writer.drawIndexed(vertices, indices, indexCount)
 *
 * CommandBuffer::drawInstances(vertices, instances)
 *  - dynamic instance data + fixed vertex data        ->
 *        DrawWriter::Instances instances(writer, vertices, {}, vertexCount);
 *        instances.append(n) << ...;
 *  - fixed vertex and instance data                   ->
 *        writer.drawInstanced(vertices, vertexCount, instances, instanceCount)
 *
 * CommandBuffer::drawIndexedInstanced(vertices, indices, instances)
 *  - dynamic instance data + fixed vertex, index data ->
 *        DrawWriter::Instances instances(writer, vertices, indices, indexCount);
 *        instances.append(n) << ...;
 *  - fixed vertex, index, and instance data           ->
 *        writer.drawIndexedInstanced(vertices, indices, indexCount, instances, instanceCount)
 *
 * NOTE: DrawWriter automatically handles failures to find or create a GPU buffer or map it to
 * be writable. All returned VertexWriters will have a non-null pointer to write to, even if it will
 * be discarded due to GPU failure at Recorder::snap() time.
 */
class DrawWriter { … };

// Appender implementations for DrawWriter that set the template on creation and provide a
// template-specific API to accumulate vertex/instance data.
class DrawWriter::Appender { … };

class DrawWriter::Vertices : private DrawWriter::Appender { … };

class DrawWriter::Instances : private DrawWriter::Appender { … };

template <typename VertexCountProxy>
class DrawWriter::DynamicInstances : private DrawWriter::Appender { … };

} // namespace skgpu::graphite

#endif // skgpu_graphite_DrawWriter_DEFINED