impeller/entity/entity_pass_target.cc

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "impeller/entity/entity_pass_target.h"

#include "impeller/renderer/texture.h"

namespace impeller {

EntityPassTarget::EntityPassTarget(const RenderTarget& render_target,
                                   bool supports_read_from_resolve)
    : target_(render_target),
      supports_read_from_resolve_(supports_read_from_resolve) {}

std::shared_ptr<Texture> EntityPassTarget::Flip(Allocator& allocator) {
  auto color0 = target_.GetColorAttachments().find(0)->second;

  if (supports_read_from_resolve_ && color0.resolve_texture) {
    // Just return the current resolve texture, which is safe to read in the
    // next render pass that'll resolve to `target_`.
    //
    // Note that this can only be done when MSAA is being used.
    return color0.resolve_texture;
  }

  if (!secondary_color_texture_) {
    // The second texture is allocated lazily to avoid unused allocations.
    TextureDescriptor new_descriptor = color0.texture->GetTextureDescriptor();
    secondary_color_texture_ = allocator.CreateTexture(new_descriptor);

    if (!secondary_color_texture_) {
      return nullptr;
    }
  }

  std::swap(color0.resolve_texture ? color0.resolve_texture : color0.texture,
            secondary_color_texture_);

  target_.SetColorAttachment(color0, 0);

  // Return the previous backdrop texture, which is safe to read in the next
  // render pass that attaches `target_`.
  return secondary_color_texture_;
}

const RenderTarget& EntityPassTarget::GetRenderTarget() const {
  return target_;
}

bool EntityPassTarget::IsValid() const {
  return !target_.GetColorAttachments().empty();
}

}  // namespace impeller