bitcount - Developer IT

What's the best way to convert from network bitcount to netmask?

- by Choy

For example, if I have a network spec like 172.20.10.0/24, "24" is the bitcount. What's the best way to convert that to a netmask like 0xffffff00 ?

Why is it useful to count the number of bits?

I've seen the numerous questions about counting the number of set bits in a insert type of input, but why is it useful? For those looking for algorithms about bit counting, look here: http://stackoverflow.com/questions/1517848/counting-common-bits-in-a-sequence-of-unsigned-longs http://stackoverflow.com/questions/472325/fastest-way-to-count-number-of-bit-transitions-in-an-unsigned-int http://stackoverflow.com/questions/109023/best-algorithm-to-count-the-number-of-set-bits-in-a-32-bit-integer

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directshow Renderstream fails with grayscale bitmaps

- by Roey

Hi all. I'm trying to create a directshow graph to playback a video composed of 8bit grayscale bitmaps. (using directshow.net.) I'm using a source filter and the vmr9 renderer. The source filter's output pin is defined using the following code : bmi.Size = Marshal.SizeOf(typeof(BitmapInfoHeader)); bmi.Width = width; bmi.Height = height;; bmi.Planes = 1; bmi.BitCount = (short)bitcount; bmi.Compression = 0; bmi.ImageSize = Math.Abs(bmi.Height) * bmi.Width * bmi.BitCount / 8; bmi.ClrUsed = bmi.BitCount <= 8 ? 256 : 0; bmi.ClrImportant = 0; //bmi.XPelsPerMeter = 0; //bmi.YPelsPerMeter = 0; bool isGrayScale = bmi.BitCount <= 8 ? true : false; int formatSize = Marshal.SizeOf(typeof(BitmapInfoHeader)); if (isGrayScale == true) { MessageWriter.Log.WriteTrace("Playback is grayscale."); /// Color table holds an array of 256 RGBQAD values /// Those are relevant only for grayscale bitmaps formatSize += Marshal.SizeOf(typeof(RGBQUAD)) * bmi.ClrUsed; } IntPtr ptr = Marshal.AllocHGlobal(formatSize); Marshal.StructureToPtr(bmi, ptr, false); if (isGrayScale == true) { /// Adjust the pointer to the beginning of the /// ColorTable address and create the grayscale color table IntPtr ptrNext = (IntPtr)((int)ptr + Marshal.SizeOf(typeof(BitmapInfoHeader))); for (int i = 0; i < bmi.ClrUsed; i++) { RGBQUAD rgbCell = new RGBQUAD(); rgbCell.rgbBlue = rgbCell.rgbGreen = rgbCell.rgbRed = (byte)i; rgbCell.rgbReserved = 0; Marshal.StructureToPtr(rgbCell, ptrNext, false); ptrNext = (IntPtr)((int)ptrNext + Marshal.SizeOf(typeof(RGBQUAD))); } } This causes Renderstream to return "No combination of intermediate filters could be found to make the connection." Please help! Thanks.

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Objects won't render when Texture Compression + Mipmapping is Enabled

- by felipedrl

I'm optimizing my game and I've just implemented compressed (DXTn) texture loading in OpenGL. I've worked my way removing bugs but I can't figure out this one: objects w/ DXTn + mipmapped textures are not being rendered. It's not like they are appearing with a flat color, they just don't appear at all. DXTn textured objs render and mipmapped non-compressed textures render just fine. The texture in question is 256x256 I generate the mips all the way down 4x4, i.e 1 block. I've checked on gDebugger and it display all the levels (7) just fine. I'm using GL_LINEAR_MIPMAP_NEAREST for min filter and GL_LINEAR for mag one. The texture is being compressed and mipmaps being created offline with Paint.NET tool using super sampling method. (I also tried bilinear just in case) Source follow: [SNIPPET 1: Loading DDS into sys memory + Initializing Object] // Read header DDSHeader header; file.read(reinterpret_cast<char*>(&header), sizeof(DDSHeader)); uint pos = static_cast<uint>(file.tellg()); file.seekg(0, std::ios_base::end); uint dataSizeInBytes = static_cast<uint>(file.tellg()) - pos; file.seekg(pos, std::ios_base::beg); // Read file data mData = new unsigned char[dataSizeInBytes]; file.read(reinterpret_cast<char*>(mData), dataSizeInBytes); file.close(); mMipmapCount = header.mipmapcount; mHeight = header.height; mWidth = header.width; mCompressionType = header.pf.fourCC; // Only support files divisible by 4 (for compression blocks algorithms) massert(mWidth % 4 == 0 && mHeight % 4 == 0); massert(mCompressionType == NO_COMPRESSION || mCompressionType == COMPRESSION_DXT1 || mCompressionType == COMPRESSION_DXT3 || mCompressionType == COMPRESSION_DXT5); // Allow textures up to 65536x65536 massert(header.mipmapcount <= MAX_MIPMAP_LEVELS); mTextureFilter = TextureFilter::LINEAR; if (mMipmapCount > 0) { mMipmapFilter = MipmapFilter::NEAREST; } else { mMipmapFilter = MipmapFilter::NO_MIPMAP; } mBitsPerPixel = header.pf.bitcount; if (mCompressionType == NO_COMPRESSION) { if (header.pf.flags & DDPF_ALPHAPIXELS) { // The only format supported w/ alpha is A8R8G8B8 massert(header.pf.amask == 0xFF000000 && header.pf.rmask == 0xFF0000 && header.pf.gmask == 0xFF00 && header.pf.bmask == 0xFF); mInternalFormat = GL_RGBA8; mFormat = GL_BGRA; mDataType = GL_UNSIGNED_BYTE; } else { massert(header.pf.rmask == 0xFF0000 && header.pf.gmask == 0xFF00 && header.pf.bmask == 0xFF); mInternalFormat = GL_RGB8; mFormat = GL_BGR; mDataType = GL_UNSIGNED_BYTE; } } else { uint blockSizeInBytes = 16; switch (mCompressionType) { case COMPRESSION_DXT1: blockSizeInBytes = 8; if (header.pf.flags & DDPF_ALPHAPIXELS) { mInternalFormat = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT; } else { mInternalFormat = GL_COMPRESSED_RGB_S3TC_DXT1_EXT; } break; case COMPRESSION_DXT3: mInternalFormat = GL_COMPRESSED_RGBA_S3TC_DXT3_EXT; break; case COMPRESSION_DXT5: mInternalFormat = GL_COMPRESSED_RGBA_S3TC_DXT5_EXT; break; default: // Not Supported (DXT2, DXT4 or any compression format) massert(false); } } [SNIPPET 2: Uploading into video memory] massert(mData != NULL); glGenTextures(1, &mHandle); massert(mHandle!=0); glBindTexture(GL_TEXTURE_2D, mHandle); commitFiltering(); uint offset = 0; Renderer* renderer = Renderer::getInstance(); switch (mInternalFormat) { case GL_RGB: case GL_RGBA: case GL_RGB8: case GL_RGBA8: for (uint i = 0; i < mMipmapCount + 1; ++i) { uint width = std::max(1U, mWidth >> i); uint height = std::max(1U, mHeight >> i); glTexImage2D(GL_TEXTURE_2D, i, mInternalFormat, width, height, mHasBorder, mFormat, mDataType, &mData[offset]); offset += width * height * (mBitsPerPixel / 8); } break; case GL_COMPRESSED_RGB_S3TC_DXT1_EXT: case GL_COMPRESSED_RGBA_S3TC_DXT1_EXT: case GL_COMPRESSED_RGBA_S3TC_DXT3_EXT: case GL_COMPRESSED_RGBA_S3TC_DXT5_EXT: { uint blockSize = 16; if (mInternalFormat == GL_COMPRESSED_RGB_S3TC_DXT1_EXT || mInternalFormat == GL_COMPRESSED_RGBA_S3TC_DXT1_EXT) { blockSize = 8; } uint width = mWidth; uint height = mHeight; for (uint i = 0; i < mMipmapCount + 1; ++i) { uint nBlocks = ((width + 3) / 4) * ((height + 3) / 4); // Only POT textures allowed for mipmapping massert(width % 4 == 0 && height % 4 == 0); glCompressedTexImage2D(GL_TEXTURE_2D, i, mInternalFormat, width, height, mHasBorder, nBlocks * blockSize, &mData[offset]); offset += nBlocks * blockSize; if (width <= 4 && height <= 4) { break; } width = std::max(4U, width / 2); height = std::max(4U, height / 2); } break; } default: // Not Supported massert(false); } Also I don't understand the "+3" in the block size computation but looking for a solution for my problema I've encountered people defining it as that. I guess it won't make a differente for POT textures but I put just in case. Thanks.

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