#include "testprec.h"
+#if wxUSE_IMAGE
+
#ifdef __BORLANDC__
#pragma hdrstop
#endif
#ifndef WX_PRECOMP
#endif // WX_PRECOMP
-#include "wx/image.h"
+#include "wx/anidecod.h" // wxImageArray
+#include "wx/palette.h"
#include "wx/url.h"
#include "wx/log.h"
#include "wx/mstream.h"
#include "wx/zstream.h"
#include "wx/wfstream.h"
+#include "testimage.h"
+
struct testData {
const char* file;
wxBitmapType type;
+ unsigned bitDepth;
} g_testfiles[] =
{
- { "horse.ico", wxBITMAP_TYPE_ICO },
- { "horse.xpm", wxBITMAP_TYPE_XPM },
- { "horse.png", wxBITMAP_TYPE_PNG },
- { "horse.ani", wxBITMAP_TYPE_ANI },
- { "horse.bmp", wxBITMAP_TYPE_BMP },
- { "horse.cur", wxBITMAP_TYPE_CUR },
- { "horse.gif", wxBITMAP_TYPE_GIF },
- { "horse.jpg", wxBITMAP_TYPE_JPEG },
- { "horse.pcx", wxBITMAP_TYPE_PCX },
- { "horse.pnm", wxBITMAP_TYPE_PNM },
- { "horse.tga", wxBITMAP_TYPE_TGA },
- { "horse.tif", wxBITMAP_TYPE_TIF }
+ { "horse.ico", wxBITMAP_TYPE_ICO, 4 },
+ { "horse.xpm", wxBITMAP_TYPE_XPM, 8 },
+ { "horse.png", wxBITMAP_TYPE_PNG, 24 },
+ { "horse.ani", wxBITMAP_TYPE_ANI, 24 },
+ { "horse.bmp", wxBITMAP_TYPE_BMP, 8 },
+ { "horse.cur", wxBITMAP_TYPE_CUR, 1 },
+ { "horse.gif", wxBITMAP_TYPE_GIF, 8 },
+ { "horse.jpg", wxBITMAP_TYPE_JPEG, 24 },
+ { "horse.pcx", wxBITMAP_TYPE_PCX, 8 },
+ { "horse.pnm", wxBITMAP_TYPE_PNM, 24 },
+ { "horse.tga", wxBITMAP_TYPE_TGA, 8 },
+ { "horse.tif", wxBITMAP_TYPE_TIFF, 8 }
};
CPPUNIT_TEST( LoadFromZipStream );
CPPUNIT_TEST( LoadFromFile );
CPPUNIT_TEST( SizeImage );
+ CPPUNIT_TEST( CompareLoadedImage );
+ CPPUNIT_TEST( CompareSavedImage );
+ CPPUNIT_TEST( SavePNG );
+ CPPUNIT_TEST( SaveTIFF );
+ CPPUNIT_TEST( SaveAnimatedGIF );
+ CPPUNIT_TEST( ReadCorruptedTGA );
+ CPPUNIT_TEST( GIFComment );
+ CPPUNIT_TEST( DibPadding );
+ CPPUNIT_TEST( BMPFlippingAndRLECompression );
CPPUNIT_TEST_SUITE_END();
void LoadFromSocketStream();
void LoadFromZipStream();
void LoadFromFile();
void SizeImage();
+ void CompareLoadedImage();
+ void CompareSavedImage();
+ void SavePNG();
+ void SaveTIFF();
+ void SaveAnimatedGIF();
+ void ReadCorruptedTGA();
+ void GIFComment();
+ void DibPadding();
+ void BMPFlippingAndRLECompression();
DECLARE_NO_COPY_CLASS(ImageTestCase)
};
void ImageTestCase::LoadFromSocketStream()
{
- // Skip this test when running on a build slave because it just keeps
- // failing erratically and sends build failure notifications when it does.
- //
- // Of course, it would be even better to understand why does it fail but so
- // far we didn't manage to do it so disable until someone can find the
- // problem.
- if ( wxGetUserId().Lower().Matches("buildslave*") )
- return;
-
if (!IsNetworkAvailable()) // implemented in test.cpp
{
wxLogWarning("No network connectivity; skipping the "
wxBitmapType type;
} testData[] =
{
- { "http://wxwidgets.org/logo9.jpg", wxBITMAP_TYPE_JPEG },
- { "http://wxwidgets.org/favicon.ico", wxBITMAP_TYPE_ICO }
+ { "http://www.wxwidgets.org/logo9.jpg", wxBITMAP_TYPE_JPEG },
+ { "http://www.wxwidgets.org/favicon.ico", wxBITMAP_TYPE_ICO }
};
for (unsigned int i=0; i<WXSIZEOF(testData); i++)
{
wxURL url(testData[i].url);
- CPPUNIT_ASSERT(url.GetError() == wxURL_NOERR);
+ WX_ASSERT_EQUAL_MESSAGE
+ (
+ ("Constructing URL \"%s\" failed.", testData[i].url),
+ wxURL_NOERR,
+ url.GetError()
+ );
wxInputStream *in_stream = url.GetInputStream();
- CPPUNIT_ASSERT(in_stream && in_stream->IsOk());
+ WX_ASSERT_MESSAGE
+ (
+ ("Opening URL \"%s\" failed.", testData[i].url),
+ in_stream && in_stream->IsOk()
+ );
wxImage img;
// NOTE: it's important to inform wxImage about the type of the image being
// loaded otherwise it will try to autodetect the format, but that
// requires a seekable stream!
- CPPUNIT_ASSERT(img.LoadFile(*in_stream, testData[i].type));
+ WX_ASSERT_MESSAGE
+ (
+ ("Loading image from \"%s\" failed.", testData[i].url),
+ img.LoadFile(*in_stream, testData[i].type)
+ );
delete in_stream;
}
case wxBITMAP_TYPE_GIF:
case wxBITMAP_TYPE_PCX:
case wxBITMAP_TYPE_TGA:
- case wxBITMAP_TYPE_TIF:
+ case wxBITMAP_TYPE_TIFF:
continue; // skip testing those wxImageHandlers which cannot
// load data from non-seekable streams
CPPUNIT_ASSERT_EQUAL( actual.GetSize().x, expected.GetSize().x );
CPPUNIT_ASSERT_EQUAL( actual.GetSize().y, expected.GetSize().y );
- const unsigned data_len = 3 * expected.GetHeight() * expected.GetWidth();
-
- WX_ASSERT_MESSAGE
+ WX_ASSERT_EQUAL_MESSAGE
(
("Resize test #%u: (%d, %d), (%d, %d)", i, st.w, st.h, st.dx, st.dy),
- memcmp(actual.GetData(), expected.GetData(), data_len) == 0
+ expected, actual
);
}
}
+void ImageTestCase::CompareLoadedImage()
+{
+ wxImage expected8("horse.xpm");
+ CPPUNIT_ASSERT( expected8.IsOk() );
+
+ wxImage expected24("horse.png");
+ CPPUNIT_ASSERT( expected24.IsOk() );
+
+ for (size_t i=0; i<WXSIZEOF(g_testfiles); i++)
+ {
+ if ( !(g_testfiles[i].bitDepth == 8 || g_testfiles[i].bitDepth == 24)
+ || g_testfiles[i].type == wxBITMAP_TYPE_JPEG /*skip lossy JPEG*/)
+ {
+ continue;
+ }
+
+ wxImage actual(g_testfiles[i].file);
+
+ if ( actual.GetSize() != expected8.GetSize() )
+ {
+ continue;
+ }
+
+
+ WX_ASSERT_EQUAL_MESSAGE
+ (
+ ("Compare test '%s' for loading failed", g_testfiles[i].file),
+ g_testfiles[i].bitDepth == 8 ? expected8 : expected24,
+ actual
+ );
+ }
+
+}
+
+enum
+{
+ wxIMAGE_HAVE_ALPHA = (1 << 0),
+ wxIMAGE_HAVE_PALETTE = (1 << 1)
+};
+
+static
+void CompareImage(const wxImageHandler& handler, const wxImage& image,
+ int properties = 0, const wxImage *compareTo = NULL)
+{
+ wxBitmapType type = handler.GetType();
+
+ const bool testPalette = (properties & wxIMAGE_HAVE_PALETTE) != 0;
+ /*
+ This is getting messy and should probably be transformed into a table
+ with image format features before it gets hairier.
+ */
+ if ( testPalette
+ && ( !(type == wxBITMAP_TYPE_BMP
+ || type == wxBITMAP_TYPE_GIF
+ || type == wxBITMAP_TYPE_ICO
+ || type == wxBITMAP_TYPE_PNG)
+ || type == wxBITMAP_TYPE_XPM) )
+ {
+ return;
+ }
+
+ const bool testAlpha = (properties & wxIMAGE_HAVE_ALPHA) != 0;
+ if (testAlpha
+ && !(type == wxBITMAP_TYPE_PNG || type == wxBITMAP_TYPE_TGA
+ || type == wxBITMAP_TYPE_TIFF) )
+ {
+ // don't test images with alpha if this handler doesn't support alpha
+ return;
+ }
+
+ if (type == wxBITMAP_TYPE_JPEG /* skip lossy JPEG */)
+ {
+ return;
+ }
+
+ wxMemoryOutputStream memOut;
+ if ( !image.SaveFile(memOut, type) )
+ {
+ // Unfortunately we can't know if the handler just doesn't support
+ // saving images, or if it failed to save.
+ return;
+ }
+
+ wxMemoryInputStream memIn(memOut);
+ CPPUNIT_ASSERT(memIn.IsOk());
+
+ wxImage actual(memIn);
+ CPPUNIT_ASSERT(actual.IsOk());
+
+ const wxImage *expected = compareTo ? compareTo : ℑ
+ CPPUNIT_ASSERT( actual.GetSize() == expected->GetSize() );
+
+ unsigned bitsPerPixel = testPalette ? 8 : (testAlpha ? 32 : 24);
+ WX_ASSERT_EQUAL_MESSAGE
+ (
+ ("Compare test '%s (%d-bit)' for saving failed",
+ handler.GetExtension(), bitsPerPixel),
+ *expected,
+ actual
+ );
+
+#if wxUSE_PALETTE
+ CPPUNIT_ASSERT(actual.HasPalette()
+ == (testPalette || type == wxBITMAP_TYPE_XPM));
+#endif
+
+ CPPUNIT_ASSERT( actual.HasAlpha() == testAlpha);
+
+ if (!testAlpha)
+ {
+ return;
+ }
+
+ WX_ASSERT_EQUAL_MESSAGE
+ (
+ ("Compare alpha test '%s' for saving failed", handler.GetExtension()),
+ *expected,
+ actual
+ );
+}
+
+static void SetAlpha(wxImage *image)
+{
+ image->SetAlpha();
+
+ unsigned char *ptr = image->GetAlpha();
+ const int width = image->GetWidth();
+ const int height = image->GetHeight();
+ for (int y = 0; y < height; ++y)
+ {
+ for (int x = 0; x < width; ++x)
+ {
+ ptr[y*width + x] = (x*y) & wxIMAGE_ALPHA_OPAQUE;
+ }
+ }
+}
+
+void ImageTestCase::CompareSavedImage()
+{
+ // FIXME-VC6: Pre-declare the loop variables for compatibility with
+ // pre-standard compilers such as MSVC6 that don't implement proper scope
+ // for the variables declared in the for loops.
+ int i;
+
+ wxImage expected24("horse.png");
+ CPPUNIT_ASSERT( expected24.IsOk() );
+ CPPUNIT_ASSERT( !expected24.HasAlpha() );
+
+ wxImage expected8 = expected24.ConvertToGreyscale();
+
+#if wxUSE_PALETTE
+ unsigned char greys[256];
+ for (i = 0; i < 256; ++i)
+ {
+ greys[i] = i;
+ }
+ wxPalette palette(256, greys, greys, greys);
+ expected8.SetPalette(palette);
+#endif // #if wxUSE_PALETTE
+
+ expected8.SetOption(wxIMAGE_OPTION_BMP_FORMAT, wxBMP_8BPP_PALETTE);
+
+ // Create an image with alpha based on the loaded image
+ wxImage expected32(expected24);
+
+ SetAlpha(&expected32);
+
+ const wxList& list = wxImage::GetHandlers();
+ for ( wxList::compatibility_iterator node = list.GetFirst();
+ node; node = node->GetNext() )
+ {
+ wxImageHandler *handler = (wxImageHandler *) node->GetData();
+
+#if wxUSE_PALETTE
+ CompareImage(*handler, expected8, wxIMAGE_HAVE_PALETTE);
+#endif
+ CompareImage(*handler, expected24);
+ CompareImage(*handler, expected32, wxIMAGE_HAVE_ALPHA);
+ }
+}
+
+void ImageTestCase::SavePNG()
+{
+ wxImage expected24("horse.png");
+ CPPUNIT_ASSERT( expected24.IsOk() );
+#if wxUSE_PALETTE
+ CPPUNIT_ASSERT( !expected24.HasPalette() );
+#endif // #if wxUSE_PALETTE
+
+ wxImage expected8 = expected24.ConvertToGreyscale();
+
+ /*
+ horse.png converted to greyscale should be saved without a palette.
+ */
+ CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG), expected8);
+
+ /*
+ But if we explicitly ask for trying to save with a palette, it should work.
+ */
+ expected8.SetOption(wxIMAGE_OPTION_PNG_FORMAT, wxPNG_TYPE_PALETTE);
+
+ CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG),
+ expected8, wxIMAGE_HAVE_PALETTE);
+
+
+ CPPUNIT_ASSERT( expected8.LoadFile("horse.gif") );
+#if wxUSE_PALETTE
+ CPPUNIT_ASSERT( expected8.HasPalette() );
+#endif // #if wxUSE_PALETTE
+
+ CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG),
+ expected8, wxIMAGE_HAVE_PALETTE);
+
+ /*
+ Add alpha to the image in such a way that there will still be a maximum
+ of 256 unique RGBA combinations. This should result in a saved
+ PNG image still being palettised and having alpha.
+ */
+ expected8.SetAlpha();
+
+ int x, y;
+ const int width = expected8.GetWidth();
+ const int height = expected8.GetHeight();
+ for (y = 0; y < height; ++y)
+ {
+ for (x = 0; x < width; ++x)
+ {
+ expected8.SetAlpha(x, y, expected8.GetRed(x, y));
+ }
+ }
+
+ CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG),
+ expected8, wxIMAGE_HAVE_ALPHA|wxIMAGE_HAVE_PALETTE);
+
+ /*
+ Now change the alpha of the first pixel so that we can't save palettised
+ anymore because there will be 256+1 entries which is beyond PNGs limit
+ of 256 entries.
+ */
+ expected8.SetAlpha(0, 0, 1);
+
+ CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG),
+ expected8, wxIMAGE_HAVE_ALPHA);
+
+ /*
+ Even if we explicitly ask for saving palettised it should not be done.
+ */
+ expected8.SetOption(wxIMAGE_OPTION_PNG_FORMAT, wxPNG_TYPE_PALETTE);
+ CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG),
+ expected8, wxIMAGE_HAVE_ALPHA);
+
+}
+
+static void TestTIFFImage(const wxString& option, int value,
+ const wxImage *compareImage = NULL)
+{
+ wxImage image;
+ if (compareImage)
+ {
+ image = *compareImage;
+ }
+ else
+ {
+ (void) image.LoadFile("horse.png");
+ }
+ CPPUNIT_ASSERT( image.IsOk() );
+
+ wxMemoryOutputStream memOut;
+ image.SetOption(option, value);
+
+ CPPUNIT_ASSERT(image.SaveFile(memOut, wxBITMAP_TYPE_TIFF));
+
+ wxMemoryInputStream memIn(memOut);
+ CPPUNIT_ASSERT(memIn.IsOk());
+
+ wxImage savedImage(memIn);
+ CPPUNIT_ASSERT(savedImage.IsOk());
+
+ WX_ASSERT_EQUAL_MESSAGE(("While checking for option %s", option),
+ true, savedImage.HasOption(option));
+
+ WX_ASSERT_EQUAL_MESSAGE(("While testing for %s", option),
+ value, savedImage.GetOptionInt(option));
+
+ WX_ASSERT_EQUAL_MESSAGE(("HasAlpha() not equal"), image.HasAlpha(), savedImage.HasAlpha());
+}
+
+void ImageTestCase::SaveTIFF()
+{
+ TestTIFFImage(wxIMAGE_OPTION_TIFF_BITSPERSAMPLE, 1);
+ TestTIFFImage(wxIMAGE_OPTION_TIFF_SAMPLESPERPIXEL, 1);
+ TestTIFFImage(wxIMAGE_OPTION_TIFF_PHOTOMETRIC, 0/*PHOTOMETRIC_MINISWHITE*/);
+ TestTIFFImage(wxIMAGE_OPTION_TIFF_PHOTOMETRIC, 1/*PHOTOMETRIC_MINISBLACK*/);
+
+ wxImage alphaImage("horse.png");
+ CPPUNIT_ASSERT( alphaImage.IsOk() );
+ SetAlpha(&alphaImage);
+
+ // RGB with alpha
+ TestTIFFImage(wxIMAGE_OPTION_TIFF_SAMPLESPERPIXEL, 4, &alphaImage);
+
+ // Grey with alpha
+ TestTIFFImage(wxIMAGE_OPTION_TIFF_SAMPLESPERPIXEL, 2, &alphaImage);
+
+ // B/W with alpha
+ alphaImage.SetOption(wxIMAGE_OPTION_TIFF_BITSPERSAMPLE, 1);
+ TestTIFFImage(wxIMAGE_OPTION_TIFF_SAMPLESPERPIXEL, 2, &alphaImage);
+}
+
+void ImageTestCase::SaveAnimatedGIF()
+{
+#if wxUSE_PALETTE
+ wxImage image("horse.gif");
+ CPPUNIT_ASSERT( image.IsOk() );
+
+ wxImageArray images;
+ images.Add(image);
+ int i;
+ for (i = 0; i < 4-1; ++i)
+ {
+ images.Add( images[i].Rotate90() );
+
+ images[i+1].SetPalette(images[0].GetPalette());
+ }
+
+ wxMemoryOutputStream memOut;
+ CPPUNIT_ASSERT( wxGIFHandler().SaveAnimation(images, &memOut) );
+
+ wxGIFHandler handler;
+ wxMemoryInputStream memIn(memOut);
+ CPPUNIT_ASSERT(memIn.IsOk());
+ const int imageCount = handler.GetImageCount(memIn);
+ CPPUNIT_ASSERT_EQUAL(4, imageCount);
+
+ for (i = 0; i < imageCount; ++i)
+ {
+ wxFileOffset pos = memIn.TellI();
+ CPPUNIT_ASSERT( handler.LoadFile(&image, memIn, true, i) );
+ memIn.SeekI(pos);
+
+ WX_ASSERT_EQUAL_MESSAGE
+ (
+ ("Compare test for GIF frame number %d failed", i),
+ images[i],
+ image
+ );
+ }
+#endif // #if wxUSE_PALETTE
+}
+
+void ImageTestCase::ReadCorruptedTGA()
+{
+ static unsigned char corruptTGA[18+1+3] =
+ {
+ 0,
+ 0,
+ 10, // RLE compressed image.
+ 0, 0,
+ 0, 0,
+ 0,
+ 0, 0,
+ 0, 0,
+ 1, 0, // Width is 1.
+ 1, 0, // Height is 1.
+ 24, // Bits per pixel.
+ 0,
+
+ 0xff, // Run length (repeat next pixel 127+1 times).
+ 0xff, 0xff, 0xff // One 24-bit pixel.
+ };
+
+ wxMemoryInputStream memIn(corruptTGA, WXSIZEOF(corruptTGA));
+ CPPUNIT_ASSERT(memIn.IsOk());
+
+ wxImage tgaImage;
+ CPPUNIT_ASSERT( !tgaImage.LoadFile(memIn) );
+
+
+ /*
+ Instead of repeating a pixel 127+1 times, now tell it there will
+ follow 127+1 uncompressed pixels (while we only should have 1 in total).
+ */
+ corruptTGA[18] = 0x7f;
+ CPPUNIT_ASSERT( !tgaImage.LoadFile(memIn) );
+}
+
+static void TestGIFComment(const wxString& comment)
+{
+ wxImage image("horse.gif");
+
+ image.SetOption(wxIMAGE_OPTION_GIF_COMMENT, comment);
+ wxMemoryOutputStream memOut;
+ CPPUNIT_ASSERT(image.SaveFile(memOut, wxBITMAP_TYPE_GIF));
+
+ wxMemoryInputStream memIn(memOut);
+ CPPUNIT_ASSERT( image.LoadFile(memIn) );
+
+ CPPUNIT_ASSERT_EQUAL(comment,
+ image.GetOption(wxIMAGE_OPTION_GIF_COMMENT));
+}
+
+void ImageTestCase::GIFComment()
+{
+ // Test reading a comment.
+ wxImage image("horse.gif");
+ CPPUNIT_ASSERT_EQUAL(" Imported from GRADATION image: gray",
+ image.GetOption(wxIMAGE_OPTION_GIF_COMMENT));
+
+
+ // Test writing a comment and reading it back.
+ TestGIFComment("Giving the GIF a gifted giraffe as a gift");
+
+
+ // Test writing and reading a comment again but with a long comment.
+ TestGIFComment(wxString(wxT('a'), 256)
+ + wxString(wxT('b'), 256)
+ + wxString(wxT('c'), 256));
+
+
+ // Test writing comments in an animated GIF and reading them back.
+ CPPUNIT_ASSERT( image.LoadFile("horse.gif") );
+
+ wxImageArray images;
+ int i;
+ for (i = 0; i < 4; ++i)
+ {
+ if (i)
+ {
+ images.Add( images[i-1].Rotate90() );
+ images[i].SetPalette(images[0].GetPalette());
+ }
+ else
+ {
+ images.Add(image);
+ }
+
+ images[i].SetOption(wxIMAGE_OPTION_GIF_COMMENT,
+ wxString::Format("GIF comment for frame #%d", i+1));
+
+ }
+
+
+ wxMemoryOutputStream memOut;
+ CPPUNIT_ASSERT( wxGIFHandler().SaveAnimation(images, &memOut) );
+
+ wxGIFHandler handler;
+ wxMemoryInputStream memIn(memOut);
+ CPPUNIT_ASSERT(memIn.IsOk());
+ const int imageCount = handler.GetImageCount(memIn);
+ for (i = 0; i < imageCount; ++i)
+ {
+ wxFileOffset pos = memIn.TellI();
+ CPPUNIT_ASSERT( handler.LoadFile(&image, memIn, true /*verbose?*/, i) );
+
+ CPPUNIT_ASSERT_EQUAL(
+ wxString::Format("GIF comment for frame #%d", i+1),
+ image.GetOption(wxIMAGE_OPTION_GIF_COMMENT));
+ memIn.SeekI(pos);
+ }
+}
+
+void ImageTestCase::DibPadding()
+{
+ /*
+ There used to be an error with calculating the DWORD aligned scan line
+ pitch for a BMP/ICO resulting in buffer overwrites (with at least MSVC9
+ Debug this gave a heap corruption assertion when saving the mask of
+ an ICO). Test for it here.
+ */
+ wxImage image("horse.gif");
+ CPPUNIT_ASSERT( image.IsOk() );
+
+ image = image.Scale(99, 99);
+
+ wxMemoryOutputStream memOut;
+ CPPUNIT_ASSERT( image.SaveFile(memOut, wxBITMAP_TYPE_ICO) );
+}
+
+static void CompareBMPImage(const wxString& file1, const wxString& file2)
+{
+ wxImage image1(file1);
+ CPPUNIT_ASSERT( image1.IsOk() );
+
+ wxImage image2(file2);
+ CPPUNIT_ASSERT( image2.IsOk() );
+
+ CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_BMP), image1, 0, &image2);
+}
+
+void ImageTestCase::BMPFlippingAndRLECompression()
+{
+ CompareBMPImage("image/horse_grey.bmp", "image/horse_grey_flipped.bmp");
+
+ CompareBMPImage("image/horse_rle8.bmp", "image/horse_grey.bmp");
+ CompareBMPImage("image/horse_rle8.bmp", "image/horse_rle8_flipped.bmp");
+
+ CompareBMPImage("image/horse_rle4.bmp", "image/horse_rle4_flipped.bmp");
+}
+#endif //wxUSE_IMAGE
+
/*
TODO: add lots of more tests to wxImage functions