0024392: TKService, Image_PixMap - use bottom-up image data storage by default

src/Graphic3d/Graphic3d_TextureRoot.cdl

@@ -92,6 +92,7 @@ is
   -- Default implementation will dynamically load image from specified path within this method
   -- (and no copy will be preserved in this class instance).
   -- Inheritors may dynamically generate the image or return cached instance.
+  -- Notice, image data should be in Bottom-Up order (see Image_PixMap::IsTopDown())!
   -- @return the image for texture.
 
   GetParams (me) returns TextureParams from Graphic3d;

src/Image/Image_PixMap.cxx

@@ -69,7 +69,7 @@ Image_PixMap::Image_PixMap()
 {
   memset (&myData, 0, sizeof(myData));
   myData.mySizeBPP   = 1;
-  myData.myTopToDown = 1;
+  myData.myTopToDown = Standard_Size(-1);
   setFormat (Image_PixMap::ImgGray);
 }
 
@@ -232,7 +232,6 @@ void Image_PixMap::Clear (Image_PixMap::ImgFormat thePixelFormat)
   myIsOwnPointer = true;
   myData.mySizeX = myData.mySizeY = myData.mySizeRowBytes = 0;
   setFormat (thePixelFormat);
-  myData.myTopToDown = 1;
 }
 
 // =======================================================================

src/Image/Image_PixMap.hxx

@@ -156,13 +156,15 @@ public: // high-level API
 
 public: // low-level API for batch-processing (pixels reading / comparison / modification)
 
-  //! Returns true if image data stored from Top to the Down (default).
-  //! Some external APIs can return bottom-up data instead
+  //! Returns TRUE if image data is stored from Top to the Down.
+  //! By default Bottom Up order is used instead
   //! (topmost scanlines starts from the bottom in memory).
+  //! which is most image frameworks naturally support.
+  //!
   //! Notice that access methods within this class automatically
   //! convert input row-index to apply this flag!
   //! You should use this flag only if interconnect with alien APIs and buffers.
-  //! @return true if image data is top-down.
+  //! @return true if image data is top-down
   inline bool IsTopDown() const
   {
     return myData.myTopToDown == 1;
@@ -170,8 +172,8 @@ public: // low-level API for batch-processing (pixels reading / comparison / mod
 
   //! Setup scanlines order in memory - top-down or bottom-up.
   //! Drawers should explicitly specify this value if current state IsTopDown() was ignored!
-  //! @param theIsTopDown - top-down flag.
-  inline void SetTopDown (bool theIsTopDown)
+  //! @param theIsTopDown top-down flag
+  inline void SetTopDown (const bool theIsTopDown)
   {
     myData.myTopToDown = (theIsTopDown ? 1 : Standard_Size(-1));
     setTopDown();