src/ui/lib/escher/paper/paper_shader_list.h

// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef SRC_UI_LIB_ESCHER_PAPER_PAPER_SHADER_LIST_H_
#define SRC_UI_LIB_ESCHER_PAPER_PAPER_SHADER_LIST_H_

#include <lib/syslog/cpp/macros.h>

#include <array>

#include "src/ui/lib/escher/util/enum_cast.h"
#include "src/ui/lib/escher/util/enum_count.h"

namespace escher {

class ShaderProgram;

// Acts as an index into a PaperShaderList (see below).
// NOTE: if we wanted to reduce the size of PaperShaderList, we could reuse the same index
// for multiple shaders.  For example, PaperDrawCallFactory currently emits separate draw calls for
// drawing shadow casters, and casting shadows from them.  So we could make kShadowCaster == 0 if we
// wanted to.  However, without more data, this would be a premature optimization.
enum class PaperShaderListSelector : uint8_t {
  kAmbientLighting = 0,
  kPointLighting = 1,
  kShadowCaster = 2,
  kShadowCasterDebug = 3,
  kEnumCount
};

// Stores shaders that will be used by items enqueued in a PaperRenderQueue.  These are generated by
// PaperDrawCallFactory, which is responsible for putting the right shader at the right index in the
// list.  Later, when PaperRenderer tells the PaperRenderQueue to generate Vulkan commands, it will
// specify the selector used to choose a shader from the list.
class PaperShaderList {
 public:
  PaperShaderList() { shaders_.fill(nullptr); }

  void set_shader(PaperShaderListSelector sel, ShaderProgram* prog) {
    auto index = EnumCast(sel);
    // It's OK to clear a shader to nullptr, but stomping on an existing shader is probably a
    // programming error by the caller.
    FX_DCHECK(prog == nullptr || shaders_[index] == nullptr);
    shaders_[index] = prog;
  }

  ShaderProgram* get_shader(PaperShaderListSelector sel) const { return shaders_[EnumCast(sel)]; }

 private:
  std::array<ShaderProgram*, EnumCount<PaperShaderListSelector>()> shaders_;
};

}  // namespace escher

#endif  // SRC_UI_LIB_ESCHER_PAPER_PAPER_SHADER_LIST_H_