printing string to the screen in winapi

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just working stuff with winapi, and i'm not sure how to approach something. my goal here is to have a control that will simply print things to the screen just like a command prompt would. for example, i would like to be a able to have a function that would very simply just add a string onto a printout rather than replace the text every call. first question, should i just try to make a brand new control that prints text to the screen in lines, or should i try modifying or subclassing the EDIT control? second quesiton, I would rather not do this with just one massive string which i would concat strings to and redraw everytime text is entered, but is there any other way?

Also, am i making mountains out of molehills and just overlooking a common control that does just this?

Posted 27-Aug-11 7:41am

FatalCatharsis

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Sergey Alexandrovich Kryukov · Accepted Answer · 2011-08-27T18:06:00

No, I don't think you will find some well-known control to do this, simply because this task is quite unusual. You need to do it from scratch. There is no such thing as "screen" it terms of any Windows object. You have to type in the desktop, which is a normal window. None of the approaches you listed can help. If you use EDIT control, it would be pretty much developing of a quite usual Windows application. If this is what you need, stop here.

If you really want to work with the desktop; it's not so easy. First, find the HWND of the desktop using the function GetDesktopWindow. Than inject new Windows procedure using SetWindowLong with the first parameter of desktop HWND and second parameter of GWL_WNDPROC. Don't forget to get all Windows procedure using SetWindowLong — you will need it to implement yours. Modify processing of the message WM_PAINT. Now, you need to organize some "virtual screen" which will reflect all text input/output of your command interpreter. In your handler of WM_PAINT provide rendering of your "virtual screen" onto desktop graphics. Simulate text caret; you may need to use timer to simulate blinking. Every change will need a call to Invalidate which will trigger sending of new WM_PAINT and re-rendering. You may want to use InvalidateRect or InvalidateRgn to improve performance by invalidating only a part of the scene.

For a command interpreter you can use available "CMD.EXE", only you will need to redirect all output (stderr and stdoutput) to your custom streams to process them in your desktop rendering procedure. Your input you can simply echo and put to redirected stdoutput via Invalidate.

This is all is quite doable but will take good amount of patience and attention to detail. Good exercise!

—SA