lokdocview: move commonly used functions and variables to common header

twipToPixel and pixelToTwip are also being used by the new TileBuffer
clsas. Lets move these utility functions to a common header,
tilebuffer.hxx

The variables for DPI and tileSize are also moved to tilebuffer.hxx

Change-Id: I9d0bec7f2aefe412df232040a7a9abc6db3e4ccb

libreofficekit/source/gtk/tilebuffer.cxx

@@ -9,14 +9,12 @@
 
 #include "tilebuffer.hxx"
 
-static const int DPI = 96;
-
-static float pixelToTwip(float fInput, float zoom)
+float pixelToTwip(float fInput, float zoom)
 {
     return (fInput / DPI / zoom) * 1440.0f;
 }
 
-static float twipToPixel(float fInput, float zoom)
+float twipToPixel(float fInput, float zoom)
 {
     return fInput / 1440.0f * DPI * zoom;
 }

libreofficekit/source/gtk/tilebuffer.hxx

@@ -19,6 +19,15 @@
 #include <LibreOfficeKit/LibreOfficeKitEnums.h>
 #include <LibreOfficeKit/LibreOfficeKitGtk.h>
 
+// We know that VirtualDevices use a DPI of 96.
+const int DPI = 96;
+// Lets use a square of side 256 pixels for each tile.
+const int nTileSizePixels = 256;
+
+float pixelToTwip(float fInput, float zoom);
+
+float twipToPixel(float fInput, float zoom);
+
 /*
   This class represents a single tile in the tile buffer.
   TODO: Extend it to support features like double buffering