Bronze Edition Guide - True BASIC

16. Graphics 133
as push buttons, edit fields and list buttons, and logical windows are where you use all
the other TrueBASIC features such as PRINT, PLOT and image handing statements
such as BOX SHOW.
It will help you to visualize how things will appear on the monitor screen if you think
of the physical window as being on top. For example, if you color an area of the logical
window with a BOX AREA statement, then you place a push button in the physical
window, the button will appear on top of the colored area. If you change the colored
area with another BOX AREA statement, then the button will still be on top.
The size and location of all windows are defined by four co-ordinates in this order;
left, right, bottom, top
The co-ordinates for windows are always relative to the whole screen.
The co-ordinates for objects inside windows are always relative to the window.
The final concept that you need to get your head around is that all windows and all
objects inside windows each have a unique identity number. The reason why we need
identities is again very simple. Suppose you have several push buttons labelled QUIT,
CANCEL and SUBMIT, then you will want to know which of them the user has clicked
on. The TC_event routine will tell you that a button has been pressed and it also gives
the ID number of the button. If you have created multiple windows, then TC_event
will also tell you the ID of the window the user is currently working with. The most
difficult concept to grasp is that you don’t need to know the value of the ID number,
because you can use a variable name instead. You are free to use any variable name
you like. Suppose you have a button that is labelled QUIT, then you might use the
variable name quit as the ID for this button.
Remember, that there is nothing magical or mystical about windows and the objects
inside them. They are just graphical images painted on the screen. However, behind
the scenes, there is a great deal of code that makes the object appear to react in a
particular way when you click the mouse inside the perimeter of the object. Take for
example a simple push button, which you create with just one very simple line of code:
CALL TC_PushBtn_create(id,”LABEL”,xl,xr,yb,yt)
You don’t need to worry about all the code that paints a rectangular area of the screen
gray, and works out where the center is so that the word LABEL is printed in the
middle in black. Nor do you have to concern yourself with working out how to color the
edges of the rectangle to give the button a 3D effect of standing proud of the
background using shadows on the bottom and right hand edges. When you click the
button these shadows are reversed momentarily to give the impression the button has
been pressed. All this code has been done for you in the library module BronzeTC.
Until now the output from your programs has been displayed on the screen in the
default font, over which you had no control. BronzeTC now gives you control over the
font, not just in the default window, but all windows, e.g.