Hello, im trying to create multiple opengl rendering contexts on different windows. For example, the function fails if hwnd is an invalid window handle or. With its multitasking and multithreading api, win32 revolutionized programming for microsoft windows. Peekmessage is a nonblocking call that returns immediately, with a message if any are waiting, or no message if none is waiting. The reason this happens is simply because peekmessage is reading messages from the message queue for its thread, whereas a message sent via sendmessage does not go via this queueessentially the sendmessage function calls the appropriate window procedure directly. I tried it with using multiple hdcs and hgrlcs and in a single thread. Getmessage will check the message queue for message, if there arent any messages in the queue it will block. The message loop is an obligatory section of code in every program that uses a graphical user interface under microsoft windows. It is typically used to dispatch a message retrieved by the getmessage function. The difference between getmessage and peekmessage ruined my. Only users with topic management privileges can see it. If you are using windows 95 or nt, the better way is to create another thread for the background processing, the main thread deal with ui and terminate the worker thread when user cancel the operation. I wonder where you will try to get translatemessage and dispatchmessage. Net class for the threads message queue management, thread message queue management is an elementary feature in inter thread.
The translatemessage function does not modify the message pointed to by the lpmsg parameter. So dispatchmessage does the actual work of processing the message. Hi since i am a newbie to win32 programming i am facing difficulty in understanding how to use these getmessage, sendmessage, postthreadmessage. An applications main thread starts its message loop after initializing the application and creating at least one window. Hi niki, thanks for your response, still, i didnt understand from your response if there is an equivalent for the threads message queue management win32 api, there must be a. Please note that buttons are not normal windows buttons, rather they are just bibltd. Finally, the message is sent to the window for processing using the dispatchmessage function.
If youve seen magazine articles and advanced programming books on these subjects, you might have been intimidated by the complexity of using multiple threads. Translates virtualkey messages into character messages. It is very important technique on using the multithreaded concepts in developing the windows gui applications. Blocking, in this case, would mean that getmessage will wait for a valid message to pop up into the message queue. In addition, peekmessage does not block if the message queue is empty, so your code will end up consuming 100% of the cpu core it runs on. Windows 7 represents only one of the oss msdn currently supports and while you can look at assembly all day, its resource intensive and not exactly fun. Peekmessage and dispatchmessage and trigger the function invokations via postthreadmessage. The message loop must call dispatchmessage the message loop does not directly act on the messages that it handles. Once we create the window, we get into the event loop, where we see the function getmessage. Does it cause any exception from the kernel or race condition. It looks to me that you want to use getmessage here, not peekmessage. That didnt worked because opengl uses all its stuff globally. Your window procedure is not magically called by the system, in effect you call it yourself indirectly by calling dispatchmessage. Dispatchmessage doesnt seem to be working within a.
Windows maintains an individual message queue for each thread that has created a window. The windows message processing and multithreaded programming. More information many windows based applications use peekmessage to retrieve messages while they are in the middle of a long process, such as printing, repaginating, or recalculating, that must be done in the background. Windows programmingmessage loop architecture wikibooks. You call msgwaitformultipleobjects to wait for more messages. Additionally a robust realtime game loop and window procedure are explained in detail. Using messages and message queues win32 apps microsoft docs. The translatemessage function does not modify the message. This is a very important concept for windows programs.
The character messages are posted to the calling threads message queue, to be read the next time the thread calls the getmessage or peekmessage function. I want to use peekmessage and supply the hwnd from the parent application, but it doesnt seem to want to update the main program. This is perfectly logical for windows programming, because generally speaking windows applications, word for example, tend to sit and do nothing until you make a move. Im rewriting a legacy multithreaded application as a service and i need to be able to post messages between threads to mimic how the application currently works. Find answers to peekmessage and accelerator keys from the expert community at experts exchange. For more information on how to do idle time processing using peekmessage, search msdn with the onidle keyword, and you will bump into pretty interesting topics. As i am doing processing i want to keep the main program from entering the not responding state. It is conventional for the event loop to call translatemessage on each message which can translate virtual keystrokes into strings. You would expect the specifications of peekmessage and getmessage to match, except that peekmessage does not block. Peekmessage and getmessage only look for messages in the queue of the calling thread. The problem with peekmessage is that it is not a waiting call, so youll keep checking messages in a tight loop, even when there is nothing to do. With peekmessage being heavily used for years by many legacy applications as the key component of a message loop, it becomes important to account for power issues in the applications.
When user moves the cursor over a button image on screen and does a leftclick below loop is run. Dispatchmessage, on the other hand, dispatches a message to a window procedure. If there are no messages in the queue it will then return nothing. While an application is in a peekmessage loop, the windows system cannot go idle. This page provide a tutorial and information on the windows message processing and multithreaded programming in the mfc windows gui environment. Peekmessage will check the message queue and return the first message. Code elsewhere in the program can also accept and dispatch messages. Apr 09, 20 i want to use peekmessage and supply the hwnd from the parent application, but it doesnt seem to want to update the main program. You neednt trigger the repaint, it is sufficient to it if something changes. If i were you i would look at what exactly the peekmessage function is doing to the msg object and what values it is returning. More information many windowsbased applications use peekmessage to retrieve messages while they are in the middle of a long process, such as printing, repaginating, or recalculating, that must be done in the background. Getmessage then waits for a message and, upon recieving one, sends it to the next step, translatemessage. I only realized it when i rechecked the documentation on peekmessage.
The difference between getmessage and peekmessage ruined. The threads run fine but only in 1 window a triangles is been drawn. If the window handle is null, dispatchmessage does nothing with the message. This is because peekmessage does not test for this itself, but rather returns whether it found a message to process. Peekmessage, which blocks until a message is received. Translatemessage may or may not post a new message to the thread queue. Peekmessage will check the message queue and return the first message it finds. Message for the first argument this is a different data structure. The debugger show it in your dispatchmessage function, because it is the nearest one with source code available. The message loop is an obligatory section of code in every program that uses a graphical user. What is the difference between getmessage and peekmessage. Peekmessage not dispatchmessage directly dispatches. Msgwaitformultipleobjects and the queue state the old. Why are translatemessage and dispatchmessage separate calls.
If so beware of further naming conflict with the lcltype unit. If the thread creates one or more windows, a message loop must be provided. Peekmessage is used in 16 bit windows to solve this kind of problem, but it is not a good solution. I have been seeing with this interface that occasionally peekmessage will thrown a couple different types of exceptions. Mar 17, 2019 hello, im trying to create multiple opengl rendering contexts on different windows. On windows 7, we have four exit routes with a possible three values and two occasions we can receive 1. Getmessage wait for message peekmessage return the first message, or return nothing if there are no messages now you cant use peekmessage like you would getmessage, heres a code example for both. Mar 07, 2012 a powerfriendly peekmessage loop exits when background processing is complete because, while an application is in a peekmessage loop, windows cannot go idle 2. If it so happens that there were two messages in your queue, the msgwaitformultipleobjects does not return immediately, because there are no new messages. Translatemessage and dispatchmessage to actually process the message after the peekmessage. The major difference between the two is that getmessage doesnt return until it finds a message to retrieve from the application queue, this allows us to free up precious cpu. Could someone please give me a suggestion how i should proceed. Waitmessage allows a thread to sleep until a message is in the queue. Next, the message is sent to the translatemessage function, which takes care of some simple tasks such as translating to unicode or not.
Peekmessage and accelerator keys solutions experts exchange. Calling translatemessage is not technically required, but problems can result if it is not called. Mar 16, 2008 well i have zero knowledge of windows programming, so take my advice with a dumptruck of salt. They cant read messages from another thread, whether in the same or a different process. If hwnd is null, peekmessage retrieves messages for any window that.
Well i have zero knowledge of windows programming, so take my advice with a dumptruck of salt. Thats because peekmessage does not block but returns immediately. Peekmessage is being used in place of getmessage, to avoid being put to sleep. Once you have finished processing the message, your windows procedure returns, dispatchmessage returns, and we go back to the beginning of the loop. The translatemessage function then translates virtualkey.
Windows message processing and multithreaded programming. Getmessage makes your process idle until there is a message to process. The reason this happens is simply because peekmessage is reading messages from the message queue for its thread, whereas a message sent via sendmessage does not go via this queueessentially the sendmessage function calls the appropriate window procedure directly without going via the queue. Getmessage will wait until theres a message available and yield the cpu. Getmessage translatemessage peekmessage dispatchmessage postmessage. This is really bad, as certain windows transactions take many messages. If the message is translated then a character message is posted to the threads message queue.
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