Introduce CPDFPageFromFPDFPage()

fpdfsdk/src/fpdf_progressive.cpp

Index: fpdfsdk/src/fpdf_progressive.cpp
diff --git a/fpdfsdk/src/fpdf_progressive.cpp b/fpdfsdk/src/fpdf_progressive.cpp
index aaa55a18f644fcef0f21884aeefcb507b0351d0a..b13eb553cce1255a90fab3152edfe5d557012f0f 100644
--- a/fpdfsdk/src/fpdf_progressive.cpp
+++ b/fpdfsdk/src/fpdf_progressive.cpp
@@ -18,16 +18,13 @@ DLLEXPORT int STDCALL FPDF_RenderPageBitmap_Start(FPDF_BITMAP bitmap,
                                                   int rotate,
                                                   int flags,
                                                   IFSDK_PAUSE* pause) {
-  if (bitmap == NULL || page == NULL)
+  if (!bitmap || !pause || pause->version != 1)
     return FPDF_RENDER_FAILED;
 
-  if (!pause)
+  CPDF_Page* pPage = CPDFPageFromFPDFPage(page);
+  if (!pPage)
     return FPDF_RENDER_FAILED;
 
-  if (pause->version != 1)
-    return FPDF_RENDER_FAILED;
-
-  CPDF_Page* pPage = (CPDF_Page*)page;
   CRenderContext* pContext = new CRenderContext;
   pPage->SetPrivateData((void*)1, pContext, DropContext);
 #ifdef _SKIA_SUPPORT_
@@ -59,16 +56,13 @@ DLLEXPORT int STDCALL FPDF_RenderPageBitmap_Start(FPDF_BITMAP bitmap,
 
 DLLEXPORT int STDCALL FPDF_RenderPage_Continue(FPDF_PAGE page,
                                                IFSDK_PAUSE* pause) {
-  if (page == NULL)
-    return FPDF_RENDER_FAILED;
-
-  if (!pause)
+  if (!pause || pause->version != 1)
     return FPDF_RENDER_FAILED;
 
-  if (pause->version != 1)
+  CPDF_Page* pPage = CPDFPageFromFPDFPage(page);
+  if (!pPage)
     return FPDF_RENDER_FAILED;
 
-  CPDF_Page* pPage = (CPDF_Page*)page;
   CRenderContext* pContext = (CRenderContext*)pPage->GetPrivateData((void*)1);
   if (pContext && pContext->m_pRenderer) {
     IFSDK_PAUSE_Adapter IPauseAdapter(pause);
@@ -80,10 +74,10 @@ DLLEXPORT int STDCALL FPDF_RenderPage_Continue(FPDF_PAGE page,
 }
 
 DLLEXPORT void STDCALL FPDF_RenderPage_Close(FPDF_PAGE page) {
-  if (!page)
+  CPDF_Page* pPage = CPDFPageFromFPDFPage(page);
+  if (!pPage)
     return;
 
-  CPDF_Page* pPage = (CPDF_Page*)page;
   CRenderContext* pContext = (CRenderContext*)pPage->GetPrivateData((void*)1);
   if (!pContext)
     return;