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Allow creating DIBs storing pixels in non-premultiplied format in wxMSW.

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wxDIB assumed that MSW always uses bitmaps in pre-multiplied pixel format but
this turns out to be wrong: some Windows functions such as ImageList_Draw()
or CreateIconIndirect() apply pre-multiplication internally and so must be
given data in non-pre-multiplied format on input.

This commit adds a possibility to create wxDIB in such format but doesn't use
it anywhere yet, this will be done in subsequent commits.

See #9050.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65959 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
This commit is contained in:
Vadim Zeitlin
2010-10-30 23:50:50 +00:00
parent a72ebcd091
commit fd90675b89
2 changed files with 51 additions and 16 deletions
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24
include/wx/msw/dib.h
View File

@@ -138,12 +138,28 @@ public:
// ------------------
#if wxUSE_IMAGE
// create a DIB from the given image, the DIB will be either 24 or 32 (if
// the image has alpha channel) bpp
wxDIB(const wxImage& image) { Init(); (void)Create(image); }
// Possible formats for DIBs created by the functions below.
enum PixelFormat
{
PixelFormat_PreMultiplied = 0,
PixelFormat_NotPreMultiplied = 1
};
// Create a DIB from the given image, the DIB will be either 24 or 32 (if
// the image has alpha channel) bpp.
//
// By default the DIB stores pixel data in pre-multiplied format so that it
// can be used with ::AlphaBlend() but it is also possible to disable
// pre-multiplication for the DIB to be usable with ImageList_Draw() which
// does pre-multiplication internally.
wxDIB(const wxImage& image, PixelFormat pf = PixelFormat_PreMultiplied)
{
Init();
(void)Create(image, pf);
}
// same as the above ctor but with the return code
bool Create(const wxImage& image);
bool Create(const wxImage& image, PixelFormat pf = PixelFormat_PreMultiplied);
// create wxImage having the same data as this DIB
wxImage ConvertToImage() const;

43
src/msw/dib.cpp
View File

@@ -658,7 +658,7 @@ wxPalette *wxDIB::CreatePalette() const
#if wxUSE_IMAGE
bool wxDIB::Create(const wxImage& image)
bool wxDIB::Create(const wxImage& image, PixelFormat pf)
{
wxCHECK_MSG( image.Ok(), false, wxT("invalid wxImage in wxDIB ctor") );
@@ -683,27 +683,46 @@ bool wxDIB::Create(const wxImage& image)
unsigned char *dstLineStart = (unsigned char *)m_data;
for ( int y = 0; y < h; y++ )
{
// copy one DIB line
// Copy one DIB line. Note that RGB components order is reversed in
// Windows bitmaps compared to wxImage and is actually BGR.
unsigned char *dst = dstLineStart;
if ( alpha )
{
for ( int x = 0; x < w; x++ )
switch ( pf )
{
// RGB order is reversed, and we need to premultiply
// all channels by alpha value for use with ::AlphaBlend.
const unsigned char a = *alpha++;
*dst++ = (unsigned char)((src[2] * a + 127) / 255);
*dst++ = (unsigned char)((src[1] * a + 127) / 255);
*dst++ = (unsigned char)((src[0] * a + 127) / 255);
*dst++ = a;
src += 3;
case PixelFormat_PreMultiplied:
// Pre-multiply pixel values so that the DIB could be used
// with ::AlphaBlend().
for ( int x = 0; x < w; x++ )
{
const unsigned char a = *alpha++;
*dst++ = (unsigned char)((src[2] * a + 127) / 255);
*dst++ = (unsigned char)((src[1] * a + 127) / 255);
*dst++ = (unsigned char)((src[0] * a + 127) / 255);
*dst++ = a;
src += 3;
}
break;
case PixelFormat_NotPreMultiplied:
// Just copy pixel data without changing it.
for ( int x = 0; x < w; x++ )
{
*dst++ = src[2];
*dst++ = src[1];
*dst++ = src[0];
*dst++ = *alpha++;
src += 3;
}
break;
}
}
else // no alpha channel
{
for ( int x = 0; x < w; x++ )
{
// RGB order is reversed.
*dst++ = src[2];
*dst++ = src[1];
*dst++ = src[0];