How do graphic libraries work?

To make graphics appear on the screen, there are several layers :

So, how do you create a graphical library from scratch? It depends on where you put the zero.

If you have only one card and one processor, you will start from step 2 by writing drivers and operating systems.

If you have a card, a processor, and also an operating system, you will start from step 3, using the features that the operating system offers and building on it.

The case that I imagine you want to know is the latter, when you already have the operating system but can not understand how libraries such as Qt, GTK +, and SDL do to draw on the screen. The answer then is: they take the responsibility of speaking with the operating system in their "language", whatever it is (Win32? GDI +? DirectX? OpenGL? Xlib? Wayland? Direct syscalls to the Linux or Windows kernel? ).

C language, for historical reasons, provides a unified () way of dealing with text files (including the screen and keyboard), but does not provide the same for graphics. In the background, the two cases go through similar layers (library for the application programmer, OS API, driver, bits and bytes for communication with computer components, until it reaches the level of the electrical current that makes everything work) p>

So it's very common to have a library, which calls another library, which calls another library, which calls an operating system dependent function, which calls the driver, which causes the pixel to appear on the screen . Check out these examples :

Note that the programmer could also use GTK + directly if he felt that wxWidgets is not offering any advantage. But if it goes down to Xlib, it would certainly be harder to port the app to Windows, or when X becomes obsolete and everyone uses Wayland. And look, I may have forgotten some layer in the above list!

Or else:

Remembering that the programmer can use Direct3D and OpenGL directly.

All this without talking about Android and iOS, which should have their own APIs ...

I'm a bit rusty with this but I think it's still like this:

#include <graphics.h>

int main() {
   initgraph();
   //faz alguma coisa aqui
   closegraph();
   return 0;
}

See available functions to make the drawings. I just can not remember if this is standard or need some specific library.

reminding you that this is for a console application. If it is to do on a system with its own system of screens, it will have to use the operating system API.

Another possibility is to access the graphics card more directly. You have to read her documentation. Not that people usually do this, but it's a possibility. In some cases just write to the graphic memory. This is the way to create a graphical library from scratch. No one does this. Nobody recommends this. It is the same as saying that you will make the operating system because you do not want to use the existing system calls .

Other than that, the question is very broad. No one comes out of the total lack of notion of how it starts to do something so complex. So to answer I would have to write a book (which I think does not exist)

To put things in perspective: no language is inherently "graphic" or "text". At some point, there needs to be a startup so the program is not blind, deaf and dumb. This preparation can be done by the program itself, or by the loading process that precedes it.

For C, at least on UNIX / Linux, the load process prepares the terrain, delivering the already opened text terminal (stdin / stdout / stderr).

Such a program may run in graphical mode, but must explicitly invoke a graphics library to "go into graphical mode". In Linux there are many libraries to choose from: GTK +, Qt (for C ++), Enlightenment, SDL, etc. The system does not impose a specific library.

In the case of SDL, everything starts by calling the SDL_Init () function.

I recommend that you use java graphical interfaces in your programs. link