Add APIs for limited use of document tagged code.

fpdfsdk/fpdf_structtree_embeddertest.cpp

+// 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.
+
+#include "public/fpdf_structtree.h"
+#include "testing/embedder_test.h"
+#include "testing/test_support.h"
+
+class FPDFStructTreeEmbeddertest : public EmbedderTest, public TestSaver {};
+
+TEST_F(FPDFStructTreeEmbeddertest, GetAltText) {
+  ASSERT_TRUE(OpenDocument("tagged_alt_text.pdf"));

[Lei Zhang, 2016/11/22 23:30:42]

Made tagged_alt_text.pdf in OpenOffice. I set the alternate text property on the
image in the doc, and the OpenOffice PDF exporter has a "tagged pdf" option.

[Tom Sepez, 2016/11/22 23:45:36]

That should be fine.  I pulled the patch and it looks like this is only 2KB or
so.

+  FPDF_PAGE page = LoadPage(0);
+  ASSERT_TRUE(page);
+
+  FPDF_STRUCTTREE struct_tree = FPDF_StructTree_GetForPage(page);
+  ASSERT_TRUE(struct_tree);
+  ASSERT_EQ(1, FPDF_StructTree_CountChildren(struct_tree));
+
+  FPDF_STRUCTELEMENT element = FPDF_StructTree_GetChildAtIndex(struct_tree, -1);
+  EXPECT_EQ(nullptr, element);
+  element = FPDF_StructTree_GetChildAtIndex(struct_tree, 1);
+  EXPECT_EQ(nullptr, element);
+  element = FPDF_StructTree_GetChildAtIndex(struct_tree, 0);
+  ASSERT_NE(nullptr, element);
+  EXPECT_EQ(0U, FPDF_StructElement_GetAltText(element, nullptr, 0));
+
+  ASSERT_EQ(1, FPDF_StructElement_CountChildren(element));
+  FPDF_STRUCTELEMENT child_element =
+      FPDF_StructElement_GetChildAtIndex(element, -1);
+  EXPECT_EQ(nullptr, child_element);
+  child_element = FPDF_StructElement_GetChildAtIndex(element, 1);
+  EXPECT_EQ(nullptr, child_element);
+  child_element = FPDF_StructElement_GetChildAtIndex(element, 0);
+  ASSERT_NE(nullptr, child_element);
+  EXPECT_EQ(0U, FPDF_StructElement_GetAltText(child_element, nullptr, 0));
+
+  ASSERT_EQ(1, FPDF_StructElement_CountChildren(child_element));
+  FPDF_STRUCTELEMENT gchild_element =
+      FPDF_StructElement_GetChildAtIndex(child_element, -1);
+  EXPECT_EQ(nullptr, gchild_element);
+  gchild_element = FPDF_StructElement_GetChildAtIndex(child_element, 1);
+  EXPECT_EQ(nullptr, gchild_element);
+  gchild_element = FPDF_StructElement_GetChildAtIndex(child_element, 0);
+  ASSERT_NE(nullptr, gchild_element);
+  ASSERT_EQ(25U, FPDF_StructElement_GetAltText(gchild_element, nullptr, 0));
+
+  char buffer[25];
+  ASSERT_EQ(25U, FPDF_StructElement_GetAltText(gchild_element, buffer,
+                                               sizeof(buffer)));
+  const char kBlackImageText[25] =
+      "\xFE\xFF\00B\00l\00a\00c\00k\00 \00I\00m\00a\00g\00e";

[Lei Zhang, 2016/11/22 23:30:42]

Is there a better way to do this?

[Tom Sepez, 2016/11/22 23:45:36]

const uint8_t kBlackImageText[25] = {
  0xfe, 0xff, 0x00 ...

+  EXPECT_EQ(0, memcmp(kBlackImageText, buffer, sizeof(buffer)));
+
+  FPDF_StructTree_Close(struct_tree);
+  FPDF_ClosePage(page);
+}