I have been all over the web looking for an answer to this, and my question is this:
How does a GUI framework work? for instance how does Qt work, is there any books or wibsites on the topic of writing a GUI framework from scratch? and also does the framework have to call methods from the operating systems GUI framework?
-- Thank you to any one who takes the time to try to answer this question, and forgive me if i misspelled anything.
In the old days we did a lot of GUI programming from scratch. It is not as hard as it seems, but it requires a few weeks to come with results.
First you need a good drawing library. Minimal functionality for this library is drawing clipped rectangles (using patterns), lines, bitmaps, and fonts. You can cheat by creating fonts as bitmaps, and clipped rectangle is just a bunch of horizontal lines.
Now you need at least drivers for mouse, keyboard, and timer (if not already provided by the operating system). In general, you will need to detect keys, symbol keys (such as shift, etc.), mouse moves and mouse clicks. Basic timer functions will allow you to detect double clicks.
Then you need to create a window data structure. This data structure needs to have coordinates i.e. a rectangle, link to parent window (if not top window), and window function i.e. the function that will be called when this window should handle some events.
Once you can draw on screen you need some rectangle algebra functions. You need at least good function to calculate intersection of rectangles, and a quick resolution of relative to absolute coordinates. For example - if your child window has parent then its' x and y should recursively be added to parent x and y until you reach top window.
At this point you have your:
- primitive graphical functions,
- window structure,
- mouse driver, keyboard driver, and timer,
- rectangle arithmetic.
Now you can write your main event harvesting function. This function will run all the time. It's purpose will be to detect events and send messages to correct windows. What is an event? Well, when you start your program, store mouse x and y coordinates. Then in a loop check if they have changed. If they have changed, find the window at that position ... and send WM_MOUSEMOVE event to it. Your harvesting function should handle:
- mouse moves
- mouse clicks
- mouse double clicks (remember last click and position, measure time and decide if it is a double click or not)
- timer events
- keyboard buffer changes
...
Now you should be able to send events to windows. But you really need a mechanism for it. It is a combination of message queue, and window procedure. It usually works like this: each window has a window procedure which commonly accepts four arguments: message id (i.e. is it mouse move, is it paint message), window handle, parameter 1 and parameter 2. You can call this window procedure directly using something like a send_message functions. Or you can send this window a message via post_message function. This will put message to the queue and window will process messages one by one, eventually receiving this one. So why should you call one messages directly and put others to the queue? Because of priority. You see, a keyboard click can wait some time before being processed. But a window redraw must complete immediately to prevent flicker and wrong data on screen.
So your harvest_events function sends messages to windows using post_message, and send_message. And your window message pump gets them using typical message pump like this:
while (pmsg = get_message() != NULL) send_message(pmsg->id, pmsg->hwnd, pmsg->p1, pmsg->p2);
get_message simply obtains message from the queue, and calls send message. Simple, huh? Well, not quite so. This way you would only receive driver messages to windows, but you also need some functions to redraw windows, move them, etc.. When you create move_window function, resize_window, show_window, and hide_window function, your window coordinates will change. Parts of other windows will be uncovered (if top window is moved or closed).You need to calculate which windows are affected by coordinate changes and send paint message to those windows (to repaint only the parts that were uncovered - remember, you have clipping drawing functions so this will work).
These functions introduces messages msg_paint, msg_move, msg_resize, msg_hide...
Last, you need to maintain hierarchy of windows. Your top window should be the desktop. It should have child windows (application top windows). These windows may have further child windows (buttons, edit boxes, etc.) The obvious structure for holding these is the window tree. When you detect mouse click you have to traverse window tree and do it in a smart way (finding out who has focus, who is modal, etc.) to send message to the right window. And when you draw you also must traverse all children to see who is uncovered and who is not. Last but not least, you need to handle mouse rectangle as top window to prevent flickering the mouse as windows are re-drawn or (using timers and msg_paint events) animated.
That's roughly it.
A GUI framework like Qt generally works by taking the existing OS's primitive objects (windows, fonts, bitmaps, etc), wrapping them in more platform-neutral and less clunky classes/structures/handles, and giving you the functionality you'll need to manipulate them. Yes, that almost always involves using the OS's own functions, but it doesn't HAVE to -- if you're designing an API to draw an OpenGL UI, for example, most of the underlying OS's GUI stuff won't even work, and you'll be doing just about everything on your own.
Either way, it's not for the faint of heart. If you have to ask how a GUI framework works, you're not even close to ready to design one. You're better off sticking with an existing framework and extending it to do the spiffy stuff it doesn't do already.
Related
I'm trying to write my own window manager. One issue I faced is that I don't understand how to define in which order windows should be displayed. The only means I found is to use xcb_configure_window. But it looks very limited to me: it only allows either to rise the window on top of all, or put it to the very bottom (no notion of layers or something). What a limited functionality :(.
What I really would like to do is to define the window order and tell X about it. Or to define multiple layers of windows (e.g, normal, above all, below all). So I could rise (or lower) the window with respect to its layer. So windows from lower layers will not ever cover windows from upper layers.
So, is there any other library function to define the order of windows apart from xcb_configure_window? Or I need to live with it? That would mean I have to track the order of windows in my window manager.
Link to relevant XCB documentation: https://www.x.org/releases/X11R7.6/doc/libxcb/tutorial/index.html#winstack
X11 only gives you the absolute minimum. There are no layers or always-over or always-under windows. You implement all the fancy stuff yourself, typically in the window manager, which is what you are writing.
There is no raw protocol request to change the stacking order of windows at once. Xlib has a function XRestackWindows which does that, but it uses one configure request per window. The pseudocode is just
for each window in the list except the first
change the stacking order to be under the previous window
That's it. Nothing more fancy than that.
You do need to track the stacking order in your WM in order to implement layers, so that when a program tries to restack a top level window, you intercept the request and only restack it within its layer.
Another possible way to implement layers is to have several transparent full-screen windows and reparent users' top-level windows to those, instead of to the root window. I'm not totally sure it will always work though, and you need to deal with transparency in one way or another, which requires transparency supporting hardware or the composite extension or possibly both.
It is the responsibility of the window manager to order the windows. A window gives hints about which type it is (popup dialog, menu window, splashscreen, toolbox, etc), the window manager then decides how to display this on the screen. This includes keeping track of the order and deciding which gets priority.
There is a X11 call to change the order (XRestackWindows), but I don't know the Xcb equivalent.
I'm trying to prevent my rendering from stopping when my window is out of focus or resizing. In addition to the resizing, if I resize my window smaller, then bigger again anything that wasn't visible when it was smaller is now black. Is there any way to fix this?
There are really two distinct things going on here. The moving/resizing problem is caused by the windows DefWindowProc function which applications use to handle messages that aren't explicitly handled by the application itself. In the case of moving or resizing, it blocks, creating a new message queue to handle most messages, but there are a few that it will still dispatch to the application's main event queue, like WM_TIMER. You can find lots more information in this answer.
The second issue is that your program only "owns" the pixels inside your window, and only those that are not covered up by other windows. When you make the window smaller, the pixels at the edge need to be overwritten to show the window border or whatever's behind the window. When the window is made bigger, some drivers automatically set the newly acquired pixels to black, while others leave them at whatever they were before (usually part of the window border). The OS doesn't remember if those pixels had some specific color the last time the window was that size, because most of the time the program doesn't care. Instead, windows sends a WM_PAINT message to indicate that the application should redraw the window. Your program should either directly handle this, or use a library like GLFW that abstracts it. In addition, you need to handle resize events by calling glViewport with the new size of the window.
I am trying to capture windows hidden behind my application. I am using windows 7 and VC++. I have tried printwindow() function which draws the both non-client and client area of hidden window, but captured window in the device context doesn't show desktop composition effects(aero effects). Instead it shows the captured window with windows 7 basic theme.
I have also tried with GetWindowDC() to retrive the DC of hidden window, and then Bitblt() it to memory DC but the captured window doesn't show non-client area (caption, close button, minimize button etc) correctly.
Anybody faced this issue?
Please help.
Click the link below. It leads to a MSDN site that lists all the existing Windows Functions ever of all history since Windows 95 up to Windows 8 (from period where Microsoft started Windows until present). It shows old windows functions of first Windows and new windows functions added for the new windows.
http://msdn.microsoft.com/en-us/library/windows/desktop/ff468919(v=vs.85).aspx
Anyway follow this site.
You will see the name of each function as a link.
Click any of them that you are interested.
Each link there leads to another MSDN site that explains all the basics knowledge that you must know about the function before using it, that you want to learn more. What that function does, its purpose, all its parameters and how to use each one, all their flags, all parameters types, return value and at last remarks section that shed more light and sometimes gives tips about the selected function.
Of course, you don't have to read all of them. Find in the list only the necessary functions to fit your needs. The functions that will solve your problem and answer your question that you posted.
By the way, I read your post, and I think that I found in the list the necessary functions that will do what you want to do, I will list them below, and say in one sentence what each does for what you need:
AnimateWindow - Enables you to produce special effects when showing or hiding windows. There are four types of animation: roll, slide, collapse or expand, and alpha-blended fade.
FlashWindow - Flashes the specified window one time. It does not change the active state of the window.
FlashWindowEx - Flashes the specified window specified number of times. It does not change the active state of the window.
Use these functions to achieve the aero effects that you want.
SetWindowPos - Changes the size, position, and Z order of a child, pop-up, or top-level window. These windows are ordered according to their appearance on the screen. The topmost window receives the highest rank and is the first window in the Z order.
Use this function to show the hidden windows on the top side (above all other windows) and on the screen front of you. The operating system will automatically draw the both non-client and client area of these windows without using any gdi, draw and paint functions yourself.
If you want these windows to return back to their previous state (where they were hidden), then save their state with GetWindowPlacement function and later call SetWindowPlacement to bring them back to their hidden state. You can try GetWindowRect and SetWindowPos instead to achieve the same goal.
I also think that you will be interested in GetWindowTheme and SetWindowTheme functions and all the draw theme functions (BackgroundEx, Edge, Icon, Text, TextEx).
There are more theme functions. Find in msdn and in other sites on the web.
We're making a user-space device driver for OS X that moves the cursor using Quartz Events, and we ran into a problem when games — especially ones that run in a windowed mode — can't properly capture the mouse pointer (= contain/keep it within the boundaries of their windows). For example, it would go outside the game window and click on the desktop or nearby inactive applications.
We could fix this if only we could detect when an active application calls CGAssociateMouseAndMouseCursorPosition.
How would you do this? Any ideas are appreciated.
I dont know if this can help you
There is an option called Focus Follows Mouse
Focus Follows Mouse - The Mouse pointer will grab automatically change focus to a new window inisde this one app if you mouse over it, instead of having to click a window to get focus, then clicking to do something.
http://wineskin.urgesoftware.com/tiki-index.php?page=Manual+4.6+Advanced+-+Options
I have written a few different mouse logical layers (for bridging different input devices, etc.). I have found that hooking into the OS level WM_INPUT event is a sure way of getting very real-time mouse position information. There is also a less rigorous solution of just polling the mouse data you need from one of Windows' very primitive DLLs. They are lightning fast. You could poll on a 10ms timer and never see performance loss on a modern machine.
You can probably figure out why I am asking this question. Even if not, it's very simple.
My question is whether it is possible to detect the use of SetCursorPos() on one's own application, without scanning other running applications for any calls to this API.
For example, if I have my cursor in a window and I call SetCursorPos(), can this window in anyway know that the cursor placement is not directly from the mouse (raw input)?
I am not oblivious to the fact that you can 'know' whether a mouse input is raw simply by checking how the position alters; for example, if the position changes from 100(X) & 100(Y) to 500(X) and 500(Y), without moving through each individual location between these two, then with certainty, something has altered the mouse position.
If anyone of you know of a way to produce 'raw mouse input', without any application being able to tell the difference between the output from a function, and that from a mouse--if there is such a difference--then that'd suffice, too.
Of course, whenever I move my mouse, the operating system I am using detects this and then appropriately moves the cursor accordingly. In practice, I should be able to alter this low level functionality as to my will?
There is no way for a window to directly determine how the mouse was moved. External applications could be using SetCursorPos(), but they could also be using lower level functions like mouse_event() or SendInput() instead. By the time the notification reach the target window, the OS has already normalized the data and any source information is lost If you really needed to detect use of SetCursorPos() or other functions, you would have to directly hook into those functions in every running process. Alternatively, you might try registering for "Raw Input" via RegisterRawInputDevices() and see if you get a corresponding notification from the mouse hardware directy, assumine those simulating functions do not trigger Raw notifications as well.