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

// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com

#include "fpdfsdk/cpdfsdk_renderpage.h"

#include <memory>
#include <utility>

#include "core/fpdfapi/render/cpdf_pagerendercache.h"
#include "core/fpdfapi/render/cpdf_pagerendercontext.h"
#include "core/fpdfapi/render/cpdf_progressiverenderer.h"
#include "core/fpdfapi/render/cpdf_renderoptions.h"
#include "core/fpdfdoc/cpdf_annotlist.h"
#include "core/fxge/cfx_renderdevice.h"
#include "fpdfsdk/cpdfsdk_helpers.h"
#include "fpdfsdk/cpdfsdk_pauseadapter.h"

namespace {

void RenderPageImpl(CPDF_PageRenderContext* pContext,
                    CPDF_Page* pPage,
                    const CFX_Matrix& matrix,
                    const FX_RECT& clipping_rect,
                    int flags,
                    const FPDF_COLORSCHEME* color_scheme,
                    bool need_to_restore,
                    CPDFSDK_PauseAdapter* pause) {
  if (!pContext->m_pOptions)
    pContext->m_pOptions = std::make_unique<CPDF_RenderOptions>();

  auto& options = pContext->m_pOptions->GetOptions();
  options.bClearType = !!(flags & FPDF_LCD_TEXT);
  options.bNoNativeText = !!(flags & FPDF_NO_NATIVETEXT);
  options.bLimitedImageCache = !!(flags & FPDF_RENDER_LIMITEDIMAGECACHE);
  options.bForceHalftone = !!(flags & FPDF_RENDER_FORCEHALFTONE);
  options.bNoTextSmooth = !!(flags & FPDF_RENDER_NO_SMOOTHTEXT);
  options.bNoImageSmooth = !!(flags & FPDF_RENDER_NO_SMOOTHIMAGE);
  options.bNoPathSmooth = !!(flags & FPDF_RENDER_NO_SMOOTHPATH);

  // Grayscale output
  if (flags & FPDF_GRAYSCALE)
    pContext->m_pOptions->SetColorMode(CPDF_RenderOptions::kGray);

  if (color_scheme) {
    pContext->m_pOptions->SetColorMode(CPDF_RenderOptions::kForcedColor);
    SetColorFromScheme(color_scheme, pContext->m_pOptions.get());
    options.bConvertFillToStroke = !!(flags & FPDF_CONVERT_FILL_TO_STROKE);
  }

  const CPDF_OCContext::UsageType usage =
      (flags & FPDF_PRINTING) ? CPDF_OCContext::Print : CPDF_OCContext::View;
  pContext->m_pOptions->SetOCContext(
      pdfium::MakeRetain<CPDF_OCContext>(pPage->GetDocument(), usage));

  pContext->m_pDevice->SaveState();
  pContext->m_pDevice->SetBaseClip(clipping_rect);
  pContext->m_pDevice->SetClip_Rect(clipping_rect);
  pContext->m_pContext = std::make_unique<CPDF_RenderContext>(
      pPage->GetDocument(), pPage->m_pPageResources.Get(),
      static_cast<CPDF_PageRenderCache*>(pPage->GetRenderCache()));

  pContext->m_pContext->AppendLayer(pPage, &matrix);

  if (flags & FPDF_ANNOT) {
    auto pOwnedList = std::make_unique<CPDF_AnnotList>(pPage);
    CPDF_AnnotList* pList = pOwnedList.get();
    pContext->m_pAnnots = std::move(pOwnedList);
    bool bPrinting =
        pContext->m_pDevice->GetDeviceType() != DeviceType::kDisplay;
    pList->DisplayAnnots(pPage, pContext->m_pDevice.get(),
                         pContext->m_pContext.get(), bPrinting, &matrix, false,
                         nullptr);
  }

  pContext->m_pRenderer = std::make_unique<CPDF_ProgressiveRenderer>(
      pContext->m_pContext.get(), pContext->m_pDevice.get(),
      pContext->m_pOptions.get());
  pContext->m_pRenderer->Start(pause);
  if (need_to_restore)
    pContext->m_pDevice->RestoreState(false);
}

}  // namespace

void CPDFSDK_RenderPage(CPDF_PageRenderContext* pContext,
                        CPDF_Page* pPage,
                        const CFX_Matrix& matrix,
                        const FX_RECT& clipping_rect,
                        int flags,
                        const FPDF_COLORSCHEME* color_scheme) {
  RenderPageImpl(pContext, pPage, matrix, clipping_rect, flags, color_scheme,
                 /*need_to_restore=*/true, /*pause=*/nullptr);
}

void CPDFSDK_RenderPageWithContext(CPDF_PageRenderContext* pContext,
                                   CPDF_Page* pPage,
                                   int start_x,
                                   int start_y,
                                   int size_x,
                                   int size_y,
                                   int rotate,
                                   int flags,
                                   const FPDF_COLORSCHEME* color_scheme,
                                   bool need_to_restore,
                                   CPDFSDK_PauseAdapter* pause) {
  const FX_RECT rect(start_x, start_y, start_x + size_x, start_y + size_y);
  RenderPageImpl(pContext, pPage, pPage->GetDisplayMatrix(rect, rotate), rect,
                 flags, color_scheme, need_to_restore, pause);
}

渲染流程：

1. 设置渲染选项
2. 渲染设备的初始化
3. 在设备上下文中添加页面对象列表
4. 渲染注释列表
5. 构造增量渲染器
6. 开始渲染
7. 恢复设备初始化状态

// Copyright 2016 PDFium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com

#ifndef CORE_FPDFAPI_RENDER_CPDF_PAGERENDERCONTEXT_H_
#define CORE_FPDFAPI_RENDER_CPDF_PAGERENDERCONTEXT_H_

#include <memory>

#include "core/fpdfapi/page/cpdf_page.h"

class CFX_RenderDevice;
class CPDF_ProgressiveRenderer;
class CPDF_RenderContext;
class CPDF_RenderOptions;

// Everything about rendering is put here: for OOM recovery
class CPDF_PageRenderContext final : public CPDF_Page::RenderContextIface {
 public:
  // Context merely manages the lifetime for callers.
  class AnnotListIface {
   public:
    virtual ~AnnotListIface() {}
  };

  CPDF_PageRenderContext();
  ~CPDF_PageRenderContext() override;

  // Specific destruction order required.
  std::unique_ptr<AnnotListIface> m_pAnnots;
  std::unique_ptr<CPDF_RenderOptions> m_pOptions;
  std::unique_ptr<CFX_RenderDevice> m_pDevice;
  std::unique_ptr<CPDF_RenderContext> m_pContext;
  std::unique_ptr<CPDF_ProgressiveRenderer> m_pRenderer;
};

#endif  // CORE_FPDFAPI_RENDER_CPDF_PAGERENDERCONTEXT_H_

CPDF_PageRenderContext 

包含了渲染选项，渲染设备，渲染上下文，注释列表，增量渲染器