Windows Mobile下画透明PNG图片的解决方案
最近一直看到有人在问这个PNG的东西,正好在工作的时候也用得到,就找了几个图片试了一下.从wince开始引入了IImage的支持,这样我们可以用IImage来load 这些图片. 大致的流程很多地方都有:
CoCreateInstance创建IImagingFactory, 然后用CreateImageFromFile创建IImage的接口,最后把这个IImage用draw的接口画到DC.但是问题在于这个Draw是没有设置transparent属性的? 这个东西应该如何操作呢? 在网上看到了一个解决方案. 就是把这个png图片转化成一张32位的bitmap,然后再透明的画到DC上.这里有一段调试成功的代码:
HBITMAP LoadPngImage2 (HDC hdc, LPCTSTR filename) { IImagingFactory* pImageFactory = 0; IImage* pImage = 0; ImageInfo imageInfo; CoInitializeEx(0, COINIT_MULTITHREADED); HBITMAP hBitmap = 0; LPBYTE lpByte; if (SUCCEEDED(CoCreateInstance(CLSID_ImagingFactory, 0, CLSCTX_INPROC_SERVER, IID_IImagingFactory, (void**)&pImageFactory))) { if (SUCCEEDED(pImageFactory->CreateImageFromFile(filename, &pImage))&& SUCCEEDED(pImage->GetImageInfo(&imageInfo))) { HDC bmpDC = CreateCompatibleDC(hdc); //LPBYTE lpByte; BITMAPINFO *pbinfo ; pbinfo = (BITMAPINFO *)calloc(1, sizeof(BITMAPINFO) + 4 * sizeof(INT)) ; if(!pbinfo) return FALSE ; pbinfo->bmiHeader.biSize = sizeof (BITMAPINFOHEADER); pbinfo->bmiHeader.biWidth = imageInfo.Width ; pbinfo->bmiHeader.biHeight = imageInfo.Height ; pbinfo->bmiHeader.biPlanes = 1; pbinfo->bmiHeader.biBitCount = 32; pbinfo->bmiHeader.biCompression = BI_ALPHABITFIELDS; pbinfo->bmiHeader.biSizeImage = 0 ; pbinfo->bmiHeader.biXPelsPerMeter = 11811; pbinfo->bmiHeader.biYPelsPerMeter = 11811; pbinfo->bmiHeader.biClrUsed = 0; pbinfo->bmiHeader.biClrImportant = 0; int *pMask = (int*)&(pbinfo->bmiColors[0]) ; *pMask++ = 0x00FF0000 ; *pMask++ = 0x0000FF00 ; *pMask++ = 0x000000FF ; *pMask++ = 0xFF000000 ; hBitmap = CreateDIBSection(NULL, pbinfo, DIB_RGB_COLORS, (void **)&lpByte, NULL, 0) ; free(pbinfo) ; if(!hBitmap || !lpByte) return FALSE ; RECT rect = {0, 0, imageInfo.Width, imageInfo.Height}; IBitmapImage *pBitmapImage; BitmapData bitmapData; bitmapData.Width = imageInfo.Width; bitmapData.Height = imageInfo.Height; bitmapData.PixelFormat = imageInfo.PixelFormat; pBitmapImage = NULL; pImageFactory->CreateBitmapFromImage(pImage, imageInfo.Width, imageInfo.Height, PIXFMT_32BPP_ARGB, InterpolationHintDefault, &pBitmapImage); pBitmapImage->LockBits(&rect, ImageLockModeRead,PIXFMT_32BPP_ARGB, &bitmapData); //transferring the pixels memcpy(lpByte, bitmapData.Scan0, imageInfo.Width * imageInfo.Height * 4); pBitmapImage->UnlockBits(&bitmapData); pBitmapImage->Release(); pImage->Release(); DeleteDC(bmpDC); } pImageFactory->Release(); } CoUninitialize(); //ProcessThePixelsWithAlphaChannel Here // vertical flip and ProcessThePixelsWithAlphaChannel here for (UINT y=0; y<imageInfo.Height/2; y++) { BYTE * pPixel = (BYTE *) lpByte + imageInfo.Width * 4 * y; BYTE * pDstPixel = (BYTE*) lpByte + imageInfo.Width * 4 * (imageInfo.Height-y-1); for (UINT x=0; x<imageInfo.Width; x++) { pPixel[0] = pPixel[0] * pPixel[3] / 255; pPixel[1] = pPixel[1] * pPixel[3] / 255; pPixel[2] = pPixel[2] * pPixel[3] / 255; pDstPixel[0] = pDstPixel[0] * pDstPixel[3] / 255; pDstPixel[1] = pDstPixel[1] * pDstPixel[3] / 255; pDstPixel[2] = pDstPixel[2] * pDstPixel[3] / 255; INT* pOrigin = (INT*)pPixel; INT* pDst = (INT*)pDstPixel; INT temp = *pOrigin; *pOrigin = *pDst; *pDst = temp; pPixel += 4; pDstPixel += 4; } } return hBitmap; }
类似的源码可以在MSDN论坛的某一个帖子中找到.但是不是非常完整且正确. 这里做了一些修正. 略去之前的那些过程,但看最后的这个for循环, 实际上做了一个垂直方向的180度翻转. 这就是说这里的接口memcpy拷贝过去的图片像素信息实际上是被翻转过的, 这个在很多camera的帧里面都有体现.