Fix a partial rendering problem

samples/pdfium_test.cc

 // Copyright (c) 2010 The Chromium 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 <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include <list>
 #include <sstream>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "image_diff_png.h"
 #include "public/fpdf_dataavail.h"
+#include "public/fpdf_edit.h"
 #include "public/fpdf_ext.h"
 #include "public/fpdf_formfill.h"
 #include "public/fpdf_text.h"
 #include "public/fpdfview.h"
 #include "testing/test_support.h"
 
 #ifdef PDF_ENABLE_V8
 #include "v8/include/libplatform/libplatform.h"
 #include "v8/include/v8.h"
 #endif  // PDF_ENABLE_V8
@@ skipping 315 matching lines @@
   FPDF_TEXTPAGE text_page = FPDFText_LoadPage(page);
   FORM_OnAfterLoadPage(page, form);
   FORM_DoPageAAction(page, form, FPDFPAGE_AACTION_OPEN);
 
   double scale = 1.0;
   if (!options.scale_factor_as_string.empty()) {
     std::stringstream(options.scale_factor_as_string) >> scale;
   }
   int width = static_cast<int>(FPDF_GetPageWidth(page) * scale);
   int height = static_cast<int>(FPDF_GetPageHeight(page) * scale);
-
-  FPDF_BITMAP bitmap = FPDFBitmap_Create(width, height, 0);
+  int alpha = FPDFPage_HasTransparency(page) ? 1 : 0;
+  FPDF_BITMAP bitmap = FPDFBitmap_Create(width, height, alpha);
   if (!bitmap) {
     fprintf(stderr, "Page was too large to be rendered.\n");
     return false;
   }
-
-  FPDFBitmap_FillRect(bitmap, 0, 0, width, height, 0xFFFFFFFF);
+  FPDF_DWORD fill_color = alpha ? 0x00000000 : 0xFFFFFFFF;
+  FPDFBitmap_FillRect(bitmap, 0, 0, width, height, fill_color);
   FPDF_RenderPageBitmap(bitmap, page, 0, 0, width, height, 0, 0);
 
   FPDF_FFLDraw(form, bitmap, page, 0, 0, width, height, 0, 0);
   int stride = FPDFBitmap_GetStride(bitmap);
   const char* buffer =
       reinterpret_cast<const char*>(FPDFBitmap_GetBuffer(bitmap));
 
   switch (options.output_format) {
 #ifdef _WIN32
     case OUTPUT_BMP:
@@ skipping 226 matching lines @@
   }
 
   FPDF_DestroyLibrary();
 #ifdef PDF_ENABLE_V8
   v8::V8::ShutdownPlatform();
   delete platform;
 #endif  // PDF_ENABLE_V8
 
   return 0;
 }