What graphics libraries and compiler to use for cross-platform?

Question

Atmel AVR

On pure C without pluses, a program is being developed to control the device (microcontroller, board, robot, etc.). avr-gcc compiler.
The program will be with visual effects. To make it easier and more visual to create effects, I want to create a window interface for visual control of visual effects.
In what direction is it better to develop? To have a windowed interface in the style of the windows of each OS, or in the form of a site when the GUI is organized through the browser? When the window interface, I wrote the code-script-conditions in the program, animated and saved (burned the program into the microcontroller). And if it's a browser, then the file is saved, and then the difficulties begin. It is necessary to somehow flash the program ... Ie. it turns out an extra step.
For example, the written program is launched on any OS, the necessary animation is created, the animation sequence is recorded and flashed into the MK.
What code should a pure C compiler (e.g. avr-gcc, gcc or mingw) produce for Intel, ARM, or LLVM?
As a GUI, I consider the following technologies:
- GTK+
- Qt
- WxWidgets
- Tcl/Tk.