Win32 API Speed Issues

I'm trying to write a software synthesiser for Windows for a university project. The project in in the prototype stage, where I have a basic Windows interface and a graphical display (rendered using the SetPixel () function).

The problem is, the program won't run at a sufficient speed so as to get a reasonable sample rate for the audio.

The code to do this will go in the WM_TIMER event, and even with the timer interval set to 0, the program is still far too slow.

How can I get the program running at a decent speed?

You can access the higher precision counter with QueryPerformanceCounter(), but without more details of how your code is structured, it is difficult to advise how to integrate it with your code.

You may well need to run your sampling code in a seperate thread at a higher priority then your UI if timing is critical. You will, however, have to be careful you don't make the UI so slow as to render the whole product useless.

Can you explain how to implement the high-resolution timer with QueryPerformanceCounter ()?

Quote:

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Originally Posted by samGwilliam

The code to do this will go in the WM_TIMER event, and even with the timer interval set to 0, the program is still far too slow.

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I agree that this should be in another thread. While your window is being painted the WM_TIMER messages are waiting in the message queue.

Multithreading is a big mystery to me.

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I have a basic Windows interface and a graphical display (rendered using the SetPixel () function).

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SetPixel is an extremely inefficient way to render your display. If you need to manipulate pixels, a better method is to create a dib section (which gives you access to the pixel data) and BitBlt it to the window when required. This approach will be an order of magnitude faster than using SetPixel.

You create a dib-section with the CreateDIBSection function. The following sample creates a 32bpp bitmap WIDTH x HEIGHT (WIDTH and HEIGHT are assumed to be constants defined by you) and selects it into a memory device context:

Code:

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    BITMAPINFO bmp  = { 0 };
    DWORD*    pBits = NULL;
    HBITMAP    hBmp  = NULL;
    HDC        hdcMem = NULL;

    bmp.bmiHeader.biSize        = sizeof(BITMAPINFOHEADER);
    bmp.bmiHeader.biWidth      = WIDTH;
    bmp.bmiHeader.biHeight      = HEIGHT;
    bmp.bmiHeader.biPlanes      = 1;
    bmp.bmiHeader.biBitCount    = 32;
    bmp.bmiHeader.biCompression = BI_RGB;

    hBmp = CreateDIBSection(NULL, &bmp, DIB_RGB_COLORS, &pBits, NULL, 0);
    hdcMem = CreateCompatibleDC(NULL);
    SelectObject(hdcMem, hBmp);

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Then you can manipulate pixels in the bitmap. This shows how to set a pixel at x,y to blue. You could create a macro to simplify pixel indexing.

Code:

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pBits[(y * WIDTH) + x] = RGB(0, 0, 0xFF);

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When you receive a WM_PAINT message, you need to blit the bitmap to the window:

Code:

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case WM_PAINT:
{
        PAINTSTRUCT ps = { 0 };

        BeginPaint(hwnd, &ps);

        BitBlt(ps.hdc, 0, 0, WIDTH, HEIGHT, hdcMem, 0, 0, SRCCOPY);

        EndPaint(hwnd, &ps);
        break;
}

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When the window needs updating, for example, after you have manipulated the pixels in your WM_TIMER handler, you should let Windows know by calling InvalidateRect. This will cause Windows to post a WM_PAINT message.

Code:

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InvalidateRect(hwnd, NULL, FALSE);

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>>> Multithreading is a big mystery to me.

Have a read through my basic MT tutorial starting there.

This has been a big help. Thanks a lot!