Flushing strategies Getting to grips with Segments

Rod Bird

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Intro

Flush is a command that perplexes Graphic segments perplex quite a few folks. I hope to clarify its their use and help you choose the most appropriate drawing and flushing strategy for managing segments within your project. The Help File is very clearly worded,

You need to manage segments as you read this document refresh your mind on each of the noted graphics commands. they consume memory. Even if you don’t use the flush command to create permanent segments you will find the current segment consumes memory as you draw.

The main purpose of flush a segment is to preserve the drawn graphics so that they may be redrawn, should redrawn. If the program window be is minimized or covered by another window. If the window and graphics have not been flushed you into a segment they will be lost. You will be looking at a blank white window when it is restored or uncovered. restored.

For the more adventurous, flush allows segments allow multiple graphic scenes to be flicked on and off screen.

The drawing history past and present

Liberty drawing commands do more than paint pixels on the screen, the drawing commands you issue are recorded in memory. The commands are recorded sequentially and grouped together in SEGMENTS. segments. You form a segment by issuing a FLUSH #1.gb "flush" command. Realize

You need to be aware that this recording is always on. From the moment the program starts and immediately after a flush command, a new CURRENT SEGMENT current segment is in play.

Flushed segments are the past, only they will be restored if the screen is minimized or covered by another window. The current segment is the present, current segment drawing will be lost unless flushed into the past or preserved in another way.

Naming and numbering

Segments are identified by an ever increasing number. The first segment created will be numbered 1, the next 2 and so on. If Even if we delete segments it makes no difference, the next segment will be numbered one higher than the last.

Liberty BASIC allows us to establish the number of a the current segment and store that in an appropriate program variable by issuing a SEGMENT variablename #1.gb "segment variablename" command. Even more conveniently it allows us to store the number directly to a system variable with a SEGMENT #1.gb "flush segmentname" command. segmentname adopts the number of the segment and can be used to name command. The one thing that catches most folks the segment when you later redraw or delete it.

A couple of things catch folk out in naming and numbering. First is that flush both saves the segment but also immediately and establishes a new segment. If you obtain the current segment number before you flush flush, then you will have the number of the soon to be flushed segment, if segment. If you obtain it after the flush flush, you have actually obtained the number of the new current segment. Simply deduct one in that situation. situation if you actually wanted the number of the last flushed segment.

Second thing is that the segmentname system variable is out of scope to the program. It can be used as a literal name in #1.gb "redraw segmentname" and #1.gb "delsegment segmentname" commands but you cannot use it as a program variable. If you establish a program variable of the same name it is an entirely different variable.

Managing segments

Segments can be deleted with DELSEGMENT (name), #1.gb "delsegment n" or #1.gb "delsegment segmentname", redrawn individually with REDRAW (name) #1.gb "redraw n" or #1.gb "redraw segmentname" or all undeleted segments redrawn with the command, REDRAW. REDRAW (name) command,#1.gb "redraw".

Redraw will paint the named segment to the front of the screen, this changes the Z order of the drawing on screen. REDRAW will appear to redraw will restore the Z order and paint undeleted segments in their original Z order.

You can erase all segments by issuing a CLS #1.gb "cls" command. This deletes all flushed segments, the current segment and wipes the screen. You can clear the current segment by issuing a DISCARD #1.gb "discard" command.

Decouple the screen and drawing history

Only the redraw and cls command have any impact on what you see on the screen, other commands act only on the segments held in memory. Delsegment (name) will have no impact on the screen, discard will have no impact on the screen but the segment (name) targeted will be deleted and the current segment will be wiped clean. deleted. Decouple the screen and the drawing history in your mind.

Manage memory It is important to manage segments as they consume memory. Even if you don’t use flush it is important to manage the current segment memory with discard. Start with a clean sheet

When you start, start with a clean sheet, use DISCARD. discard. Think what is in your current segment, think what you have flushed already . You might use CLS cls if you wanted to start completely fresh.

????? is CLS recorded as the first command in a segment????????

Memory use is zero and there are no forgotten drawing commands.

 'good practice to start with a clean sheet 
 #1.gb "cls" 
 'or 
 #1.gb "discard" 

Static graphics

If you are painting graphics that will not be changed, say a Company perhaps a company logo then simply draw and flush once.

Memory use is managed to one segment.

 'this is the static graphic example 
 nomainwin 
 WindowWidth = 600 
 WindowHeight = 400 
 UpperLeftX = (DisplayWidth-WindowWidth)/2 
 UpperLeftY = (DisplayHeight-WindowHeight)/2 
 graphicbox #1.gb, 50,25,500,300 
 open "Static Graphic Example" for window_nf as #1 
 #1 "trapclose [quit]" 
 
 'put the pen down and set the font 
 'note cls has no impact on these settings 
 #1.gb "down ; font comic_sans 48" 
 
 'good practice to start with a clean sheet 
 #1.gb "cls" 
 
 'draw my static graphics 
 #1.gb "fill cyan ; backcolor red ; color red" 
 #1.gb "place 100 50 ; boxfilled 300 150" 
 #1.gb "place 300 150 ; circlefilled 100" 
 #1.gb "backcolor cyan ; color red" 
 #1.gb "place 50 100 ;\1" 
 
 'now flush the graphics once and once only 
 #1.gb "flush" 
 wait 
 
 'click on the title bar of the windows and 
 'slide the window off screen and back, 
 'the graphics are retained. Rem out the 
 'flush command and try again. 
 
 [quit] 
 close #1 
 end 

Refreshed graphics

If you are painting fresh graphics, that completely replace the previous graphics, then you must DELSEGMENT delsegment the previous segment prior to drawing and flushing the next. That way there is only ever one segment in memory. This is a task that can get folks tied in knots. If you find that your program runs out of memory it is probably because you are not obtaining the correct segment number to delete.

Memory use is managed to one segment.

 'this is the refreshed graphic example, only one segment 
 'is ever retained in memory. 
 nomainwin 
 WindowWidth = 600 
 WindowHeight = 400 
 UpperLeftX = (DisplayWidth-WindowWidth)/2 
 UpperLeftY = (DisplayHeight-WindowHeight)/2 
 button #1.b, "Draw Graphic", [nextdrawing], UL, 250, 340 
 textbox #1.tb 350, 340, 100, 25 
 graphicbox #1.gb, 50,25,500,300 
 open "Refreshed Graphic Example" for window_nf as #1 
 #1 "trapclose [quit]" 
 
 'put the pen down and set the font 
 'note cls has no impact on these settings 
 #1.gb "down ; font comic_sans 48" 
 
 'good practice to start with a clean sheet 
 #1.gb "cls" 
 
 drawing=1 
 wait 
 
 [nextdrawing] 
 'first delete the last segment, it does not matter that 
 'first time round this loop there isn't a segment to delete 
 'Liberty will ignore the command 
 #1.gb "delsegment seg" 
 
 'now paint over the last graphics on screen 
 if drawing=1 then 'draw graphics 1 
 #1.gb "fill pink ; backcolor red ; color red" 
 #1.gb "place 100 50 ; boxfilled 300 150" 
 #1.gb "place 300 150 ; circlefilled 100" 
 #1.gb "backcolor pink" 
 #1.gb "place 50 100 ;\1" 
 end if 
 if drawing=2 then 'draw graphics 2 
 #1.gb "fill yellow ; backcolor green ; color green" 
 #1.gb "place 300 50 ; boxfilled 400 200" 
 #1.gb "place 300 200 ; circlefilled 100" 
 #1.gb "backcolor yellow" 
 #1.gb "place 250 50 ;\2" 
 end if 
 if drawing=3 then 'draw graphics 3 
 #1.gb "fill cyan ; backcolor yellow ; color yellow" 
 #1.gb "place 100 200 ; boxfilled 350 250" 
 #1.gb "place 100 200 ; circlefilled 50" 
 #1.gb "place 350 200 ; circlefilled 50" 
 #1.gb "backcolor cyan ; color yellow" 
 #1.gb "place 200 170 ;\3" 
 end if 
 
 drawing=drawing+1 
 if drawing=4 then drawing=1 
 
 'now flush the graphics and store the segment 
 'number in the variable seg 
 #1.gb "flush seg" 
 
 'The seg variable is catching the segment id and will 
 'increase everytime through the loop 
 
 'print the segment id number for info 
 'note the name variable "seg" is for internal use. 
 
 'to obtain and use the segment number in a variable 
 'of your own, use segment variablename 
 'this will provide the current segment number, 
 'deduct one to get the true number of the last 
 'flushed segment. 
 #1.gb "segment currentsegmentnumber" 
 lastflushed=currentsegmentnumber-1 
 #1.tb "Seg ID:";lastflushed 
 wait 
 
 [quit] 
 close #1 
 end 

Animated graphics

If you are painting animated graphics by overdrawing and redrawing repetitively you must manage memory and repetitively DISCARD discard the current segment. The screen will behave as you expect but unless you DISCARD discard the current segment history memory use will build.

Memory use is minimal.

 nomainwin 
 WindowWidth = 600 
 WindowHeight = 400 
 UpperLeftX = (DisplayWidth-WindowWidth)/2 
 UpperLeftY = (DisplayHeight-WindowHeight)/2 
 graphicbox #1.gb, 50,25,500,300 
 open "Animated Graphic Example" for window_nf as #1 
 #1 "trapclose [quit]" 
 #1.gb "down" 
 
 
 x=100 
 y=100 
 dx=10 
 dy=10 
 
 timer 17, [draw] 
 wait 
 
 [draw] 
 'discard the current drawing history 
 #1.gb "discard" 
 
 'overdraw, move and draw the ball 
 oldx=x 
 oldy=y 
 x=x+dx 
 y=y+dy 
 if x>475 then x=475 : dx=dx*-.9 
 if x<25 then x=25 : dx=dx*-.9 
 if y>275 then y= 275 : dy=dy*-.9 
 if y<25 then y=25 : dy=dy*-.9 
 #1.gb "backcolor buttonface ; color buttonface" 
 #1.gb "place ";oldx;" ";oldy 
 #1.gb "circlefilled 25" 
 #1.gb "backcolor red ; color red" 
 #1.gb "place ";x;" ";y 
 #1.gb "circlefilled 25" 
 wait 
 
 
 [quit] 
 timer 0 
 close #1 
 end 

Background and foreground graphics

If you are going to have a mostly static background and some constantly changing foreground graphics, say sliders or dials then draw the background, FLUSH flush that as the first segment. You will retain that segment. Now draw and FLUSH flush the foreground segment. Next time through DELSEGMENT delsegment the foreground segment REDRAW redraw the background and then draw and FLUSH flush the new foreground.

Memory use will not exceed two segments.

 'this is the background graphic example, only two segments 
 'are ever retained in memory. 
 nomainwin 
 WindowWidth = 600 
 WindowHeight = 400 
 UpperLeftX = (DisplayWidth-WindowWidth)/2 
 UpperLeftY = (DisplayHeight-WindowHeight)/2 
 button #1.b, "Draw Graphic", [nextdrawing], UL, 250, 340 
 graphicbox #1.gb, 50,25,500,300 
 open "Refreshed Graphic Example" for window_nf as #1 
 #1 "trapclose [quit]" 
 
 'put the pen down and set the font 
 'note cls has no impact on these settings 
 #1.gb "down ; font comic_sans 48" 
 
 'good practice to start with a clean sheet 
 #1.gb "cls" 
 
 'draw the background 
 #1.gb "fill pink ; backcolor red ; color red" 
 #1.gb "place 100 50 ; boxfilled 300 150" 
 #1.gb "place 300 150 ; circlefilled 100" 
 #1.gb "backcolor pink" 
 #1.gb "place 50 100 ;\1" 
 
 'now flush as the named segment "backgroundimage" 
 #1.gb "flush backgroundimage" 
 
 drawing=2 
 wait 
 
 
 [nextdrawing] 
 'first delete the last foreground segment, it does not matter that 
 'first time round this loop it isn't defined 
 'Liberty will ignore the command 
 #1.gb "delsegment foregroundimage" 
 
 'redraw the background using its segment name 
 #1.gb "redraw backgroundimage" 
 
 'now paint the new foreground image 
 'notice that the foreground images do not use 
 'full screen fills. 
 if drawing=2 then 'draw graphics 2 
 #1.gb "backcolor green ; color green" 
 #1.gb "place 300 50 ; boxfilled 400 200" 
 #1.gb "place 300 200 ; circlefilled 100" 
 #1.gb "backcolor red" 
 #1.gb "place 180 120 ;\2" 
 end if 
 if drawing=3 then 'draw graphics 3 
 #1.gb "backcolor yellow ; color yellow" 
 #1.gb "place 100 200 ; boxfilled 350 250" 
 #1.gb "place 100 200 ; circlefilled 50" 
 #1.gb "place 350 200 ; circlefilled 50" 
 #1.gb "backcolor red ; color yellow" 
 #1.gb "place 230 170 ;\3" 
 end if 
 
 drawing=drawing+1 
 if drawing=4 then drawing=2 
 
 'now flush the current history as the new foreground segment 
 'using the foregroundimage name 
 #1.gb "flush foregroundimage" 
 wait 
 
 
 [quit] 
 close #1 
 end 

Multiple segment graphics

If you want to get fancy you can maintain several segments in memory and change the order they appear on screen. Now most often this strategy will use partial or transparent graphics. By that I mean they will fill only parts of the screen. If you use Fills fills they will cover graphics behind. The segments are maintained in memory in the Z order they were created. They can be pulled to the front of the screen with REDRAW (name). And appear to change redraw. So changing the Z order on screen. If the segment has a full screen fill in it, all graphics will be hidden when that segment is redrawn. You might choose to do this and have a background segment, in this way you can hide and show any segments you wish.

Memory use builds depending on segments used.