Compute (un-)premultiply_table at compile time

Change-Id: I34e624fcd5d11d02c26e775f5acdddec1fca9d87
Reviewed-on: https://gerrit.libreoffice.org/64428
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

include/vcl/BitmapTools.hxx

@@ -28,10 +28,10 @@ namespace com { namespace sun { namespace star { namespace geometry { struct Int
 namespace vcl {
 namespace bitmap {
 
-typedef sal_uInt8 (*lookup_table)[256];
+typedef std::array<std::array<sal_uInt8, 256>, 256> lookup_table;
 
-lookup_table VCL_DLLPUBLIC get_premultiply_table();
-lookup_table VCL_DLLPUBLIC get_unpremultiply_table();
+VCL_DLLPUBLIC lookup_table const & get_premultiply_table();
+VCL_DLLPUBLIC lookup_table const & get_unpremultiply_table();
 
 /**
  * Intended to be used to feed into CreateFromData to create a BitmapEx. RGB data format.

vcl/headless/svpgdi.cxx

@@ -1654,7 +1654,7 @@ void SvpSalGraphics::drawMask( const SalTwoRect& rTR,
     }
     sal_Int32 nStride;
     unsigned char *mask_data = aSurface.getBits(nStride);
-    vcl::bitmap::lookup_table unpremultiply_table = vcl::bitmap::get_unpremultiply_table();
+    vcl::bitmap::lookup_table const & unpremultiply_table = vcl::bitmap::get_unpremultiply_table();
     for (long y = rTR.mnSrcY ; y < rTR.mnSrcY + rTR.mnSrcHeight; ++y)
     {
         unsigned char *row = mask_data + (nStride*y);
@@ -1762,7 +1762,7 @@ Color SvpSalGraphics::getPixel( long nX, long nY )
     cairo_destroy(cr);
 
     cairo_surface_flush(target);
-    vcl::bitmap::lookup_table unpremultiply_table = vcl::bitmap::get_unpremultiply_table();
+    vcl::bitmap::lookup_table const & unpremultiply_table = vcl::bitmap::get_unpremultiply_table();
     unsigned char *data = cairo_image_surface_get_data(target);
     sal_uInt8 a = data[SVP_CAIRO_ALPHA];
     sal_uInt8 b = unpremultiply_table[a][data[SVP_CAIRO_BLUE]];
@@ -2096,8 +2096,9 @@ void SvpSalGraphics::releaseCairoContext(cairo_t* cr, bool bXorModeAllowed, cons
         sal_Int32 nUnscaledExtentsRight = nExtentsRight * m_fScale;
         sal_Int32 nUnscaledExtentsTop = nExtentsTop * m_fScale;
         sal_Int32 nUnscaledExtentsBottom = nExtentsBottom * m_fScale;
-        vcl::bitmap::lookup_table unpremultiply_table = vcl::bitmap::get_unpremultiply_table();
-        vcl::bitmap::lookup_table premultiply_table = vcl::bitmap::get_premultiply_table();
+        vcl::bitmap::lookup_table const & unpremultiply_table
+            = vcl::bitmap::get_unpremultiply_table();
+        vcl::bitmap::lookup_table const & premultiply_table = vcl::bitmap::get_premultiply_table();
         for (sal_Int32 y = nUnscaledExtentsTop; y < nUnscaledExtentsBottom; ++y)
         {
             unsigned char *true_row = target_surface_data + (nStride*y);

vcl/source/bitmap/BitmapTools.cxx

@@ -8,6 +8,11 @@
  *
  */
 
+#include <sal/config.h>
+
+#include <array>
+#include <utility>
+
 #include <vcl/BitmapTools.hxx>
 
 #include <sal/log.hxx>
@@ -268,7 +273,7 @@ BitmapEx* CreateFromCairoSurface(Size aSize, cairo_surface_t * pSurface)
     cairo_surface_flush(pPixels);
     unsigned char *pSrc = cairo_image_surface_get_data( pPixels );
     unsigned int nStride = cairo_image_surface_get_stride( pPixels );
-    vcl::bitmap::lookup_table unpremultiply_table = vcl::bitmap::get_unpremultiply_table();
+    vcl::bitmap::lookup_table const & unpremultiply_table = vcl::bitmap::get_unpremultiply_table();
     for( unsigned long y = 0; y < static_cast<unsigned long>(aSize.Height()); y++ )
     {
         sal_uInt32 *pPix = reinterpret_cast<sal_uInt32 *>(pSrc + nStride * y);
@@ -727,7 +732,7 @@ void CanvasCairoExtractBitmapData( BitmapEx const & aBmpEx, Bitmap & aBitmap, un
     ::Color aColor;
     unsigned int nAlpha = 255;
 
-    vcl::bitmap::lookup_table premultiply_table = vcl::bitmap::get_premultiply_table();
+    vcl::bitmap::lookup_table const & premultiply_table = vcl::bitmap::get_premultiply_table();
     for( nY = 0; nY < nHeight; nY++ )
     {
         ::Scanline pReadScan;
@@ -1046,45 +1051,51 @@ void CanvasCairoExtractBitmapData( BitmapEx const & aBmpEx, Bitmap & aBitmap, un
         return bRet;
     }
 
-    static sal_uInt8 unpremultiply(sal_uInt8 c, sal_uInt8 a)
+    static constexpr sal_uInt8 unpremultiply(sal_uInt8 c, sal_uInt8 a)
     {
         return (a == 0) ? 0 : (c * 255 + a / 2) / a;
     }
 
-    static sal_uInt8 premultiply(sal_uInt8 c, sal_uInt8 a)
+    static constexpr sal_uInt8 premultiply(sal_uInt8 c, sal_uInt8 a)
     {
         return (c * a + 127) / 255;
     }
 
-    lookup_table get_unpremultiply_table()
+    template<int... Is> static constexpr std::array<sal_uInt8, 256> make_unpremultiply_table_row_(
+        int a, std::integer_sequence<int, Is...>)
     {
-        static bool inited;
-        static sal_uInt8 unpremultiply_table[256][256];
+        return {unpremultiply(Is, a)...};
+    }
 
-        if (!inited)
-        {
-            for (int a = 0; a < 256; ++a)
-                for (int c = 0; c < 256; ++c)
-                    unpremultiply_table[a][c] = unpremultiply(c, a);
-            inited = true;
-        }
+    template<int... Is> static constexpr lookup_table make_unpremultiply_table_(
+        std::integer_sequence<int, Is...>)
+    {
+        return {make_unpremultiply_table_row_(Is, std::make_integer_sequence<int, 256>{})...};
+    }
 
+    lookup_table const & get_unpremultiply_table()
+    {
+        static constexpr auto unpremultiply_table = make_unpremultiply_table_(
+            std::make_integer_sequence<int, 256>{});
         return unpremultiply_table;
     }
 
-    lookup_table get_premultiply_table()
+    template<int... Is> static constexpr std::array<sal_uInt8, 256> make_premultiply_table_row_(
+        int a, std::integer_sequence<int, Is...>)
     {
-        static bool inited;
-        static sal_uInt8 premultiply_table[256][256];
+        return {premultiply(Is, a)...};
+    }
 
-        if (!inited)
-        {
-            for (int a = 0; a < 256; ++a)
-                for (int c = 0; c < 256; ++c)
-                    premultiply_table[a][c] = premultiply(c, a);
-            inited = true;
-        }
+    template<int... Is> static constexpr lookup_table make_premultiply_table_(
+        std::integer_sequence<int, Is...>)
+    {
+        return {make_premultiply_table_row_(Is, std::make_integer_sequence<int, 256>{})...};
+    }
 
+    lookup_table const & get_premultiply_table()
+    {
+        static constexpr auto premultiply_table = make_premultiply_table_(
+            std::make_integer_sequence<int, 256>{});
         return premultiply_table;
     }