techno game dev forum

                  QB64 GRAPHICS
   Welcome to this tutorial. Here i will attempt to help the newcommer understand the legacy QBasic graphics
ideas compared to the new QB64 graphic commands and how to use them. I will use some terms to describe things and
define these terms next.

TERMS
   Legacy = QBasic or QB45
   QB64 = The new underscored keywords
   Graphic surface = a set sized screen of pixels at a certain amount of colours
   Pages = a number of associated graphic surfaces all the same size and colour depth
   Colour Depth = maximum number of colours that can be displayed on a graphics surface
   Statement = a BASIC keyword used to invoke a command with correct parameters
   Monitor = computer screen
   Mode = a particular legacy screen
   Handle = Identifing label (a name)


LEGACY SCREEN's
   In the old DOS QBasic a user could only create fixed legacy screens in size and colour depth. In QBasic a
user would create this one graphic window by using the statement SCREEN with a number. For example the main graphic
screens that QBasic could create are:

SCREEN 7
SCREEN 9
SCREEN 12
SCREEN 13

   The resolutions of these old screens are:

SCREEN 7   320 x 200 x 16 colours      at 4 pages   
SCREEN 9   640 x 350 x 16 colours      at 2 pages   
SCREEN 12   640 x 480 x 16 colours      at 1 page
SCREEN 13   320 x 200 x 256   colours      at 1 page

   When the programmer creates one of these screens one does it by invoking the SCREEN statement with the
desired screen number. It is immediately created and made visual , so its seen. On todays modern computer monitors
that have huge resolutions these old screen will appear to be very small. Never the less they can be made to fill
the entire monitor screen by using the keyboard command ALT + ENTER.


QB64 SCREEN's

   The programmer can still use the above QBasic syntax of creating a screen or use the QB64 only _NEWIMAGE.
   Newimage allows the user to create a graphic surface. This surface has a horizontal size and a vertical
size and a colour depth.
   The colour depth is indicated by using the legacy MODE number (0,1,2,7,8,9,10,11,12,13) or stateing the
colour depth as 256 or 32.
   The programmer indicates the horizontal pixel size , the vertical pixel size and the number of colors with
the arguments in the statement declaration.
For legacy screens the programmer indicates the color depth by using the Screen number (Mode) as the colour depth
variable. To create the same legacy screen with the _NEWIMAGE command the user would do:

Handle& = _NEWIMAGE(640,480,7)   'Legacy QBasic Screen 7
Handle& = _NEWIMAGE(640,480,9)   'Legacy QBasic Screen 9
Handle& = _NEWIMAGE(640,480,12)   'Legacy QBasic Screen 12
Handle& = _NEWIMAGE(640,480,13)   'Legacy QBasic Screen 13



   The HANDLE& is either the keyword SCREEN or a variable name composed by the author. Here are two examples:

SCREEN  _NEWIMAGE(640,480,12)      'immediately create and make visable
GraphicSurface& = _NEWIMAGE(640,480,12)   'immediately create but is not visable

   Whats the differences? When the SCREEN statement is used as in the first example QB64 immediately creates a
640 pixel wide by 480 pixel deep with Legacy SCREEN 12 size at 16 colours and makes it immediately visable on the
users computer monitor. When the user creates a surface with a Handle name QB64 allocates a negative number that
isnt in use to identify the identity of that surface. Secondly QB64 immediately creates a 640 pixel wide by 480
pixel deep with 16 colours surface. It does not make this surface visable. Which means that it exists and is
located in memory but is not actually shown.
   Interestingly the user can use the print statement on this surface to display the negative number assigned
to that surface. Please note that the number   -1 (negative one) is reserved to indicate that an error has occured.
So if your Surface is -1 then it isnt created! and carnt be used. So how would the user do this to illustrate the
handle number? Like this example

REM
GraphicSurface& = _NEWIMAGE(640,480,16)   'create the equivalent Legacy Screen 12
SCREEN  GraphicSurface&         'make this Surface visable
PRINT GraphicSurface&         'print the surfaces handle number
SLEEP
SYSTEM

   So the user can replicate the older DOS graphic screens but what about newer sized screens? Well with
_NEWIMAGE the user can create any sized screen that they desire with 32 bit colours. This screen can be 8 pixels
square up to 1000's of pixels square! Now even though you can make a 2,500 pixel screen the average computer
monitor can not show the entire surface on the screen. What you will see is part of the screen. If you use your
mouse cursor to click on the title bar of this screen and hold the button down you can slide it sideways to see its
complete size. The user is better off using standard sizes that most monitors can display like full screen monitor
resolutions.

clippy and that bunch bugg me big time