Add new public APIs to find the z-order for links and widgets.

fpdfsdk/src/fpdfformfill.cpp

Index: fpdfsdk/src/fpdfformfill.cpp
diff --git a/fpdfsdk/src/fpdfformfill.cpp b/fpdfsdk/src/fpdfformfill.cpp
index 170ae15799393909682d5931a2689e1f32a165b9..272e781cc2ed3cbe80cc0b368965ed827afc26f5 100644
--- a/fpdfsdk/src/fpdfformfill.cpp
+++ b/fpdfsdk/src/fpdfformfill.cpp
@@ -34,18 +34,17 @@ CPDFSDK_PageView* FormHandleToPageView(FPDF_FORMHANDLE hHandle,
 
 }  // namespace
 
-DLLEXPORT int STDCALL FPDPage_HasFormFieldAtPoint(FPDF_FORMHANDLE hHandle,
-                                                  FPDF_PAGE page,
-                                                  double page_x,
-                                                  double page_y) {
+DLLEXPORT int STDCALL FPDFPage_HasFormFieldAtPoint(FPDF_FORMHANDLE hHandle,
+                                                   FPDF_PAGE page,
+                                                   double page_x,
+                                                   double page_y) {
   if (!page || !hHandle)
     return -1;
-  CPDF_Page* pPage = (CPDF_Page*)page;
 
-  nonstd::unique_ptr<CPDF_InterForm> pInterForm(
-      new CPDF_InterForm(pPage->m_pDocument, FALSE));
-  CPDF_FormControl* pFormCtrl =
-      pInterForm->GetControlAtPoint(pPage, (FX_FLOAT)page_x, (FX_FLOAT)page_y);
+  CPDF_Page* pPage = (CPDF_Page*)page;
+  CPDF_InterForm interform(pPage->m_pDocument, FALSE);
+  CPDF_FormControl* pFormCtrl = interform.GetControlAtPoint(
+      pPage, (FX_FLOAT)page_x, (FX_FLOAT)page_y, nullptr);
   if (!pFormCtrl)
     return -1;
 
@@ -56,6 +55,28 @@ DLLEXPORT int STDCALL FPDPage_HasFormFieldAtPoint(FPDF_FORMHANDLE hHandle,
   return pFormField->GetFieldType();
 }
 
+DLLEXPORT int STDCALL FPDPage_HasFormFieldAtPoint(FPDF_FORMHANDLE hHandle,
+                                                  FPDF_PAGE page,
+                                                  double page_x,
+                                                  double page_y) {
+  return FPDFPage_HasFormFieldAtPoint(hHandle, page, page_x, page_y);
+}
+
+DLLEXPORT int STDCALL FPDFPage_FormFieldZOrderAtPoint(FPDF_FORMHANDLE hHandle,
+                                                      FPDF_PAGE page,
+                                                      double page_x,
+                                                      double page_y) {
+  if (!page || !hHandle)
+    return -1;
+
+  CPDF_Page* pPage = (CPDF_Page*)page;
+  CPDF_InterForm interform(pPage->m_pDocument, FALSE);
+  int z_order = -1;
+  (void)interform.GetControlAtPoint(pPage, (FX_FLOAT)page_x, (FX_FLOAT)page_y,
+                                    &z_order);
+  return z_order;
+}
+
 DLLEXPORT FPDF_FORMHANDLE STDCALL
 FPDFDOC_InitFormFillEnvironment(FPDF_DOCUMENT document,
                                 FPDF_FORMFILLINFO* formInfo) {