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Mac Forum / Programming / Mac Programming / February 2006PNG Resource with Alpha Channel?
How can I load an image resource with an alpha? I've been looking at CGImageCreateWithPNGDataProvider and CGImageCreateWithJPEGDataProvider, however neither appear to support alpha channels. I tried saving PNG with transparency from Photoshop, but it crashed my app upon trying to load it. In the past I used QuickDraw and it would load PICT resources with alpha just fine. I'm open to using other formats such as TIFF or PICT, but I can't find any reference for it. Thanks, Steven Walker Walker Effects www.walkereffects.com > How can I load an image resource with an alpha? I've been looking at > CGImageCreateWithPNGDataProvider and CGImageCreateWithJPEGDataProvider, > however neither appear to support alpha channels. I tried saving PNG > with transparency from Photoshop, but it crashed my app upon trying to > load it. Have you tried libpng? http://www.libpng.org/pub/png/libpng.html > In the past I used QuickDraw and it would load PICT resources with > alpha just fine. I'm open to using other formats such as TIFF or PICT, [quoted text clipped - 5 lines] > Walker Effects > www.walkereffects.com I have not tried libpng... but I'd really like to stay within the Carbon/Quartz API. Certainly other programmers must be using alpha channels with image resources. Ok, I figured it out! The PNG format -does- support alpha channels, it's just that I was relying on Photoshop to save it correctly. I just download the free SuperPNG format plugin from fnordware and it works perfectly! If anyone else runs into this issue, they can download SuperPNG from: http://fnordware.com/superpng Walker in article 1129153316.094950.225310@g49g2000cwa.googlegroups.com, steve@walkereffects.com at steve@walkereffects.com wrote on 10/12/05 2:41 PM: > Ok, I figured it out! The PNG format -does- support alpha channels, > it's just that I was relying on Photoshop to save it correctly. I just [quoted text clipped - 3 lines] > If anyone else runs into this issue, they can download SuperPNG from: > http://fnordware.com/superpng And for those who don't see the point in paying insane amounts of money for Photoshop, they can just use the free-in-your-Applications-folder GraphicConverter, which does a marvelous and convenient job of all your alpha channel handling needs. I actually IB'd up some hotkeys for Add Alpha and Show Alpha commands since I use it so much to convert the .bmp image and mask files the Windows guys give me. typedef struct { size_t width; size_t height; size_t bitsPerComponent; size_t bitsPerPixel; size_t bytesPerRow; size_t size; CGImageAlphaInfo ai; CGColorSpaceRef cs; unsigned char *data; CMProfileRef prof; } BitmapInfo; bool readBitmapInfo(GraphicsImportComponent gi, BitmapInfo *bi) { ComponentResult result; ImageDescriptionHandle imageDescH = NULL; ImageDescription *desc; Handle profile = NULL; result = GraphicsImportGetImageDescription(gi, &imageDescH); if( noErr != result || imageDescH == NULL ) { return false; } desc = *imageDescH; bi->width = desc->width; bi->height = desc->height; bi->bitsPerComponent = 8; bi->bitsPerPixel = 32; bi->bytesPerRow = (bi->bitsPerPixel * bi->width + 7)/8; bi->ai = (desc->depth == 32) ? kCGImageAlphaFirst : kCGImageAlphaNoneSkipFirst; bi->size = bi->bytesPerRow * bi->height; bi->data = (unsigned char*) malloc(bi->size); bi->cs = NULL; bi->prof = NULL; if( imageDescH != NULL) DisposeHandle((Handle)imageDescH); return true; } bool getBitmapData(GraphicsImportComponent gi, BitmapInfo *bi) { GWorldPtr gWorld; QDErr err = noErr; Rect boundsRect = { 0, 0, bi->height, bi->width }; ComponentResult result; if( bi->data == NULL ) { return false; } err = NewGWorldFromPtr( (GWorldPtr*)&gWorld, (unsigned long)k32ARGBPixelFormat, (const Rect*)&boundsRect, (CTabHandle)NULL, (GDHandle)NULL, 0, (Ptr)(bi->data), bi->bytesPerRow ); if (noErr != err) { return false; } if( (result = GraphicsImportSetGWorld(gi, gWorld, NULL)) != noErr ) { DisposeGWorld(gWorld); return false; } if( (result = GraphicsImportDraw(gi)) != noErr ) { DisposeGWorld(gWorld); return false; } DisposeGWorld(gWorld); return true; } //caller should call free( outBitMapInfo->data ) after use outBitMapInfo bool GetBitmapFromPNGFile(FSSpec* lpszFilename,BitmapInfo *outBitMapInfo) { OSStatus theErr = noErr; bool bRet = false; if ( !lpszFilename || !outBitMapInfo ) return false; FInfo theFinfo; if ( ::FSpGetFInfo(lpszFilename,&theFinfo) != noErr ) { //file not exist return false; } GraphicsImportComponent gi; theErr = GetGraphicsImporterForFile(lpszFilename,&gi); if ( theErr != noErr ) return false; if (!readBitmapInfo(gi,outBitMapInfo)) { CloseComponent(gi); //get bitmaoInfo err return false; } bRet = getBitmapData(gi,outBitMapInfo); CloseComponent(gi); return bRet; } NOTES:outBitMapInfo->data is a pixmap, bitsPerPixel is 32, first byte is alpha, if it is 0 means this > pix is transparence.(value from 0 to 255) > you * posted via http://www.mymac.ws * please report abuse to http://xinbox.com/mymac other image format can get pixmap too, such as tiff,jepg etc. //caller should call free( outBitMapInfo->data ) after use outBitMapInfo bool GetBitmapFromTIFFFile(FSSpec* lpszFilename,BitmapInfo *outBitMapInfo) { OSStatus theErr = noErr; bool bRet = false; if ( !lpszFilename || !outBitMapInfo ) return false; FInfo theFinfo; if ( ::FSpGetFInfo(lpszFilename,&theFinfo) != noErr ) { //file not exist return false; } GraphicsImportComponent gi; theErr = GetGraphicsImporterForFile(lpszFilename,&gi); if ( theErr != noErr ) return false; if (!readBitmapInfo(gi,outBitMapInfo)) { CloseComponent(gi); //get bitmaoInfo err return false; } bRet = getBitmapData(gi,outBitMapInfo); CloseComponent(gi); return bRet; > } jacobd, about png * posted via http://www.mymac.ws * please report abuse to http://xinbox.com/mymac |
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