Is it possible to control pixels on the screen just from plain C or plain C++ without any opengl / directx hassle?

Question

Well, I want to know.. maybe others too.

Is it possible to control each pixel separately on a screen by programming, especially C or C++?

Do you need special control over the drivers for the current screen? Are there operating systems which allow you to change pixels (for example draw a message/overlay on top of everything)?

Or does windows support this maybe in it's WinApi?

Edit:

I am asking this question because I want to make my computer warn me when I'm gaming and my processor gets too hot. I mainly use Windows but I have a dual boot ubuntu distro.

Answer 1

Let's look at each bit at a time:

Is it possible to control each pixel separately on a screen by programming, especially C or C++?

Possibly. It really depends on the graphics architecture, and in many modern systems, the actual screen surface (that is "the bunch of pixels appearing on the screen") is not directly under software control - at least not from "usermode" (that is, from an application that you or I can write - you need to write driver code, and you need to co-operate sufficiently with the existing graphics driver).

It is generally accepted that drawing the data into an off-screen buffer and using a BitBlt [BitBlockTransfer] function to copy the content onto the screen is the prefferred way to do this sort of thing.

So, in reality, you probably can't manipulate each pixel ON the screen - but you may be able to appear like you do.

Do you need special control over the drivers for the current screen?

Assuming you could get direct access to the screen memory, your code certainly will have to have cooperation with the driver - otherwise, who's to say that what you want to appear on the screen doesn't get overwritten by something else [e.g. you want full screen access, and the clock-updater updates the time on screen every once a minute on top of what you draw, etc].

You may be able to set the driver into a mode where you have a "hole" that allows you to access the screen memory as a big "framebuffer". I don't think there's an easy way to do this in Windows. I don't remember one from back in 2003-2005 when I wrote graphics drivers for a living.

Are there operating systems which allow you to change pixels (for example draw a message/overlay on top of everything)?

It is absolutely possible to create an overlay layer in the hardware of modern graphics cards. That's generally how video playback works - the video is played into a piece of framebuffer memory that is overlaid on top of the other graphics. You need help from the driver, and this is definitely available in the Windows API, via DirectX as far as I remember.

Or does windows support this maybe in it's WinApi?

Probably, but to answer precisely, we need to understand better what you are looking to do.

Edit: In your particular use-case, I would have thought that making sounds or ejecting the CD/DVD drive may be a more suitable opton. It can be hard to overlay something on top of the graphics drawn by a game, because games often try to use as much as possible of the available graphics resource, and you will probably have a hard time finding a way that works even for the most simple use-cases - never mind something that works for multiple different categories of games using different drawing/engine/graphics libraries. I'm also not entirely sure it's anything to worry overly about, since modern CPU's are pretty tolerant to overheating, so the CPU will just slow down, possibly grind to a halt, but it will not break - even if you take the heatsink off, it won't go wrong [no, I don't suggest you try this!]

Answer 2

Every platform supports efficient raw pixel block transfer "aka BitBlt()", so if you really want to go to frame buffer level you can allocate a bitmap and use pointers to set its contents directly then with one line of code efficiently flip this memory chunk into video ram buffer. Of course it is not as efficient as working with PCI framebuffers directly, but on the other hand this approach (BitBlt) was fast enough even in Win95 days to port Wolfenstein 3d on Pentium CPU WITHOUT the use of WinG.

HOWEVER, a care must be taken while creating this bitmap to match its format (i.e. RGB 16 bits, or 32 bits etc...) with actual mode that device is in, otherwise the graphics sub-system will do a lengthy recoding/dithering which will completely kill your speed.

So depending on your goals, If you want a 3d game your performance will suck with this approach. If you want just to render some shapes and dont need more than 10-15fps - this will work without diving into any device-driver levels.

Here is a few tips for overlaying in Windows:

hdc = GetDC(0);//returns hdc for the whole screen and is VERY fast

You can take HDC for screen and do a BItBlt(hdc, ..... SRCCOPY) to flip blocks of raster efficiently. There are also pre-defined Windows Handles for desktop but I dont recall the exact mechanics but if you are on multiple monitors you can get HDC for each desktop, look at "GetDesktopWindow", "GetDC" and the like...

Answer 3

The lower you go, the more hassle you'll run into.

If you want raw pixel manipulation you might check out http://www.libsdl.org/ which helps you mitigate the hassle of creating surfaces/windows and that kind of stuff.

Linux has a few means to get you even lower if you want (ie without "windows" or "xwindows" or anything of the sort, just the raw screen), look in to the Linux Frame Buffer if you're interested in that.

Delving even lower (such as doing things with your own OS), the BIOS will let you go into certain video modes, this is what OS installers tend to use (at least they used to, some of the fancier ones don't anymore). This isn't the fastest way of doing things, but can get you into the realm of showing pixels in a few assembly instructions.

And of course if you wanted to do your own OS and take advantage of the video card (bypass the BIOS), you're then talking about writing video drivers and such, which is obviously a substantial amount of work :)

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Re overlay messages ontop of the screen and that sort of thing, windows does support that sort of thing, so I'm sure you can do it with the WinAPI, although there are likely libraries that would make that easier. I do know you don't need to delve too deep to do that sort of thing though.