Programming guideline of WinDom

General rules

A redraw function (as every event function) has the following structure:

void a_redraw_function ( WINDOW *win) {
	...;
}

The parameter win is the descriptor of the window that has to be redrawed. Let's give some important remarks to design this redraw function.

Fist of all, one should not clip anything (i.e. use the VDI clipping functions) inside the redraw function. The clippping zone is handled by EvntWindom() (by using the AES rectangle list).
When you perform VDI calls, you can use the VDI virtual workstation opened by WindCreate(). The handle of this workstation is given by the variable win->graf.handle.
The content of a window often depends on the sliders positions and the size of the window. For that purpose, several field of the window descriptor are devoted to help you managing sliders. These are win->xpos, win->ypos, win->xpos_max and win->ypos_max. For more details, read the section about the (!url [sliders] [Window sliders]).
By convention, the first thing to do in the redraw function is to call the function WindClear() to draw the background. This function can be parametrized by the user.

In the next section, we'll see some examples that create windows. You'll see also how to attach data to a window using the Windom DataAttach() funciton.