\nThe hardware folks had this mouse wheel thing they were making,\nand they needed a way to get applications to support the mouse.\nNow, one way of doing this was to say,\n“Well, we’ll start selling this wheel mouse,\nbut no applications can use it until the next version of Windows\nis released, one that supports the wheel.”\nOf course, that would have meant waiting until Windows NT 4\ncame out, and who know when that would be.\nPlus it meant that people would have to upgrade Windows\nin order to take advantage of their fancy new mouse.\nAs you can imagine, they weren’t too pleased with the\n“wait a few years” plan.\n<\/P>\n
\nIn the interim, they proposed a stopgap mechanism for applications\nto respond to the mouse wheel.\nEnter the \n(These next few paragraphs summarize what is\n\nalready spelled out in MSDN<\/A>;\nyou can skip them if you already know how the messages work.)\n<\/P>\n \nFirst, let’s look at \nOn the other hand, the \nI’ll summarize these differences in a table,\nsince people seem to like tables so much.\n<\/P>\nzmouse.h<\/CODE> header file and its\nMSH_MOUSEWHEEL<\/CODE> registered message.\nWhen you installed the wheel mouse driver,\nit listened for wheel events from the hardware and posted\nthis new message when the mouse wheel turned,\nand applications could just respond to either\nthe WM_MOUSEWHEEL<\/CODE> message\n(if running on a version of Windows that supported the message)\nor the MSH_MOUSEWHEEL<\/CODE> message\n(if running on an older version of Windows that didn’t).\nUnfortunately, the two messages behave differently,\nso it’s not a simple matter of writing\n<\/P>\n\nif (uMsg == WM_MOUSEWHEEL || uMsg == g_msgWheel) {\n … do wheel stuff …\n}\n<\/PRE>\nWM_MOUSEWHEEL<\/CODE>.\nThis message is delivered to the window that has focus\n(in the SetFocus<\/CODE> sense).\nIf the window procedure doesn’t handle the message\nand just passes it through to the DefWindowProc<\/CODE> function,\nthen the DefWindowProc<\/CODE> function forward the message\nto the window’s parent.\nIn this way, the WM_MOUSEWHEEL<\/CODE> message\nautomatically “bubbles outward” from the focus window\nup the parent chain until somebody finally handles the\nmessage (or it goes all the way to the top without being handled at all).\n<\/P>\nMSH_MOUSEWHEEL<\/CODE> message\nworks from the outside in.\nIt is delivered to the foreground window\n(in the SetForegroundWindow<\/CODE> sense).\nIf the window procedure doesn’t want to handle the message,\nit can forward the message to child windows of its choice,\nuntil one of them returns TRUE<\/CODE> to indicate that\nthe message was handled, or until no further candidates exist.\n<\/P>\n