GL_NV_multisample_coverage & Texture alpha

Hi,

in my application if there is support for GL_NV_multisample_coverage extension, I ask for a CSAA Pixel format.
The ChoosePixelFormatARB returns a pixel format without alpha bits

±—±----±---------±-------±-----±-----------------±—±---±—±--------------+
| ID | Type| Flags | Buffer | pType| Color |Dept|Alph|Sten| Accum |
±—±----±---------±-------±-----±-----------------±—±---±—±--------------+
| 83 | ICD | 00008205 | DOUBLE | RGBA | 32 ( 8- 8- 8- 0) | 24 | 0 | 64 | (16-16-16-16) |

Why is that?
This is the code I use to get the pixel format.
Am I missing something in the parameters I pass to the ChoosePixelFormatARB() function?


        int ChooseBestCSAAPixelFormat(IntPtr testHdc, out int samples, wglChoosePixelFormatARB ChoosePixelFormatARB)
        {

            samples = 0;

            const int WGL_SAMPLE_BUFFERS_ARB = 0x2041;
            const int WGL_COVERAGE_SAMPLES_NV = 0x2042;
            const int WGL_COLOR_SAMPLES_NV = 0x20B9;
            const int WGL_DOUBLE_BUFFER_ARB = 0x2011;

            CSAAPixelFormat[] csaaPixelFormats = new CSAAPixelFormat[]
                                                     {
                                                         new CSAAPixelFormat(4, 8, "8x CSAA"),
                                                         new CSAAPixelFormat(4, 16, "16x CSAA"),
                                                         new CSAAPixelFormat(8, 8, "8xQ (Quality) CSAA"),
                                                         new CSAAPixelFormat(8, 16, "16xQ (Quality) CSAA")
                                                     };

            int totalCSAAFormats = csaaPixelFormats.Length; //  static_cast<int>(sizeof (csaaPixelFormats)/ sizeof (CSAAPixelFormat));

            int[] attributes = new int[]
                                   {
                                       WGL_SAMPLE_BUFFERS_ARB, 1,
                                       WGL_COLOR_SAMPLES_NV, 0,
                                       WGL_COVERAGE_SAMPLES_NV, 0,
                                       WGL_DOUBLE_BUFFER_ARB, 1,
                                       0,0
                                   };

            int returnedPixelFormat;
            uint numFormats;
            bool bStatus;
         
            for (int i = totalCSAAFormats - 1; i >= 0; --i)
            {

                attributes[3] = samples = csaaPixelFormats[i].numColorSamples;
                attributes[5] = csaaPixelFormats[i].numCoverageSamples;

                bStatus = ChoosePixelFormatARB(testHdc, attributes, null, 1, out returnedPixelFormat, out numFormats);
                  
                if (bStatus && numFormats > 0)
                {
#if DEBUG
                    PFList(testHdc); // Prints pixel format details 
#endif
                    return returnedPixelFormat;
                                   }
            }

            return 0;

        }