Basics
A useful method of having a program interacting with the user is through a menu. However, menu's fall under a broad category. So what is a menu? A menu must have:
- List(s) of possible actions that the user can perform
- A method of selecting items from the list(s)
Here's a chunk of code that will create a simple menu with a header(Test Menu), 4 items (A,B,C, and Quit), and allow the user to select an item. All the other optional stuff will be added later.
;Hard-coded menu routine
;
;inputs: none
;
;outputs: menu
;
;destroyed: all
;
menuStart: ;Start of menu routine
bcall(_ClrLCDFull) ;Display the Header
ld hl,txtHeader
call dispHeader
ld hl,txtItem1 ;Display Items
call dispItem
ld hl,txtItem2
call dispItem
ld hl,txtItem3
call dispItem
ld hl,txtItemQuit
call dispItem
menuLoop: ;Scan key loop to get user input
bcall(_GetKey)
cp k1 ;If user pressed 1, do action 1
jr z,item1
cp k2 ;If user pressed 2, do action 2
jr z,item2
cp k3 ;If user pressed 3, do action 3
jr z,item3
cp k4 ;If user pressed 4, quit
jr z,quit
jr menuLoop ;Else, invalid input. Wait for user to input new key
item1: ;Action 1
bcall(_ClrLCDFull)
ld bc,0
ld (curRow),bc
ld hl,txtSelect1
bcall(_PutS)
bcall(_GetKey)
jr menuStart
item2: ;Action 2
bcall(_ClrLCDFull)
ld bc,0
ld (curRow),bc
ld hl,txtSelect2
bcall(_PutS)
bcall(_GetKey)
jr menuStart
item3: ;Action 3
bcall(_ClrLCDFull)
ld bc,0
ld (curRow),bc
ld hl,txtSelect3
bcall(_PutS)
bcall(_GetKey)
jr menuStart
quit: ;quit the program
bcall(_ClrLCDFull)
ret
;dispHeader
;
;displays the header centered and at the top
;
;Inputs: HL points to null-terminating string
;
;Output: text displayed to string, top center right and inverse text
;
;Destroyed: bc,hl
;
;Note: text string must be large text and take up the full line
;(use blank spaces to fill in gaps)
;
dispHeader: ;displays the header centered and at the top
ld bc,$0
ld (curRow),bc
set textInverse,(IY+TextFlags)
bcall(_PutS)
res textInverse,(IY+TextFlags)
ld hl,0
ld (curRow),hl
ret
;dispItem
;
;displays menu items at the start of the next line
;
;Inputs: HL points to null-terminating string
;
;Output: text displayed
;
;Destroyed: all
;
dispItem: ;displays menu items at the start of the next line
push hl
bcall(_NewLine)
pop hl
bcall(_PutS)
ret
;========================================
;data
;========================================
txtHeader:
.db " Test Menu ",0
txtItem1:
.db "1:A",0
txtItem2:
.db "2:B",0
txtItem3:
.db "3:C",0
txtSelect1:
.db "You have selected A",0
txtSelect2:
.db "You have selected B",0
txtSelect3:
.db "You have selected C",0
txtItemQuit:
.db "4:Quit",0
Hopefully from the code you'll be able to understand the general flow.
First, the program runs menuStart, which displays the menu header and items to the display with the sub-routines dispHeader and dispItem.
Once the menu has been displayed, wait for a user input.
If the user presses "1", do action 1 (display "You have selected A")
If the user presses "2", do action 2
If the user presses "3", do action 3
If the user presses "4", quit
For a simple menu, this isn't too bad. However, it's bland, and void of features. So, let's add some features.
Cursor
To give the user some convenience, we'll add a cursor. The cursor allows the user to input up or down and use enter to select an item besides just pressing the corresponding number.
To do so, we'll need some code that will draw the cursor:
;curDraw
;
;Draws the cursor
;
;Inputs: C holds the highlighted item
;
;Outputs: Cursor displayed
;
;Destroyed: A
;
curDraw:
set textInverse,(IY+TextFlags) ;set inverse text
xor a
ld (curCol),a
ld a,c
ld (curRow),a
add a,$30 ;Character offset
bcall(_PutC)
ld a,':'
bcall(_PutC)
res textInverse,(IY+TextFlags)
ret
And, we'll also need some code to erase the cursor:
;curErase
;
;Erase the cursor
;
;Inputs: C highlighted item
;
;Ouputs: Cursor erased
;
;Destroyed: A
;
curErase:
xor a
ld (curCol),a
ld a,c
ld (curRow),a
add a,$30 ;Character offset
bcall(_PutC)
ld a,':'
bcall(_PutC)
ret
What happens if the user presses up/down/enter? We'll need to add code to deal with the new key presses.
;Updated menuloop
;Stuff with asterisks are new
*ld c,1* ;add this to menuStart to set initial cursor location
menuLoop: ;Scan key loop to get user input
*call curDraw*
*push bc* ;save C for later
bcall(_GetKey)
*pop bc* ;we'll need this for some routines with the new keypresses
*cp kup*
*jr z, mUp*
*cp kdown*
*jr z, mDown*
*cp kenter*
*jr z, selection*
cp k1 ;If user pressed 1, do action 1
jr z,item1
cp k2 ;If user pressed 2, do action 2
jr z,item2
cp k3 ;If user pressed 3, do action 3
jr z,item3
cp k4 ;If user pressed 4, quit
jr z,quit
jr menuLoop ;Else, invalid input. Wait for user to input new key
Move the cursor up:
;mUp
;
;moves cursor up
;
;inputs: C highlighted item
;
;Ouputs: updated cursor place stored in C
;
;Destroyed: A
;
;Notes: still need to call curDraw to re-draw the cursor
;
mUp:
call curErase ;erase the cursor
ld a,c ;check if the cursor is out of bounds
cp 1
jr z,menuLoop
dec c ;if not, decrease and return
jr menuLoop
…And, down:
;mDown
;
;moves cursor down
;
;Inputs: C highlighted item
;
;Outputs: updated cursor place sctored in C
;
;Destroyed:
;
;Notes: still need to call curDraw to re-draw the cursor
;
mDown:
call curErase ;erase the cursor
ld a,c ;check if the cursor is out of bounds
cp 4
jr z,menuLoop
inc c ;if not, increase and return
jr menuLoop
This bit of code will be called when the user presses enter:
selection:
ld a,c
cp 1
jr z,item1
cp 2
jr z,item2
cp 3
jr z,item3
jr quit
"2-D" Menus
Instead of only having the choice up and down, why not categorize items and then display the categories left to right? An example of this is the OS's math menu.
The code for 2 dimensional menus is much more complicated than the standard 1 dimensional menu, but is still manageable for the calculator. Not only do you have to keep track of which item is currently highlighted, you also need to keep track of which group that item is part of.
Since there are enough differences between the code for a 1 dimensional and 2 dimensional menu, I'll post the code in it's entirety. Be aware that it's a lot longer.
This menu has 4 items in each group, with 3 groups.
menuStart: ;Start of menu routine
bcall(_ClrLCDFull) ;Display the Header
ld b,1 ;Which group is being displayed
dispMenu: ;display the menu
ld c,1 ;Which item is highlighted
push bc
ld hl,txtHeader ;display the header
call dispHeader
ld a,b
cp 1
jr nz,dispMenu2
ld b,3
ld hl,txtItem1_1 ;Display Items in GA
call dispItems
jr dispMenu4
dispMenu2:
cp 2
jr nz,dispMenu3
ld b,3
ld hl,txtItem2_1 ;Display Items in GB
call dispItems
jr dispMenu4
dispMenu3:
ld b,3
ld hl,txtItem3_1 ;Display Items in GC
call dispItems
dispMenu4: ;Since every group has a quit, display it here
bcall(_NewLine)
ld hl,txtItemQuit
bcall(_PutS)
pop bc
menuLoop: ;Scan key loop to get user input
call curDraw
push bc ;save BC for later
bcall(_GetKey)
pop bc ;we'll need this for some routines with the new keypresses
cp kleft
jr z,mLeft
cp kright
jr z,mRight
cp kup
jr z, mUp
cp kdown
jr z, mDown
cp kenter
jr z, selection
cp k1 ;If user pressed 1, do action 1
jr z,item1
cp k2 ;If user pressed 2, do action 2
jr z,item2
cp k3 ;If user pressed 3, do action 3
jp z,item3
cp k4 ;If user pressed 4, quit
jp z,quit
jr menuLoop ;Else, invalid input. Wait for user to input new key
mUp:
call curErase ;erase the cursor
ld a,c ;check if the cursor is out of bounds
cp 1
jr z,menuLoop
dec c ;if not, decrease and return
jr menuLoop
mDown:
call curErase ;erase the cursor
ld a,c ;check if the cursor is out of bounds
cp 4
jr z,menuLoop
inc c ;if not, increase and return
jr menuLoop
mRight: ;change group
ld a,b ;check if already as far right as possible
cp 3
jr z,menuLoop
inc b
jp dispMenu
mLeft: ;change group
ld a,b ;check if already as far right as possible
cp 1
jr z,menuLoop
dec b
jp dispMenu
selection:
ld a,c
cp 1
jr z,item1
cp 2
jr z,item2
cp 3
jr z,item3
jp quit
item1: ;Action 1
push bc
bcall(_ClrLCDFull)
pop bc
ld de,0
ld (curRow),de
ld a,b
cp 1
jr nz,item1B
ld hl,txtSelect1_1 ;action 1 for group A
jr item1Done
item1B:
cp 2
jr nz,item1C
ld hl,txtSelect2_1 ;action 1 for group B
jr item1Done
item1C:
ld hl,txtSelect3_1 ;action 1 for group C
item1Done:
bcall(_PutS) ;we'll display the text now
bcall(_GetKey)
jp menuStart
item2: ;Action 2
push bc
bcall(_ClrLCDFull)
pop bc
ld de,0
ld (curRow),de
ld a,b
cp 1
jr nz,item2B
ld hl,txtSelect1_2 ;action 2 for group A
jr item2Done
item2B:
cp 2
jr nz,item2C
ld hl,txtSelect2_2 ;action 2 for group B
jr item2Done
item2C:
ld hl,txtSelect3_2 ;action 2 for group C
item2Done:
bcall(_PutS)
bcall(_GetKey)
jp menuStart
item3: ;Action 3
push bc
bcall(_ClrLCDFull)
pop bc
ld de,0
ld (curRow),de
ld a,b
cp 1
jr nz,item3B
ld hl,txtSelect1_3 ;action 3 for group A
jr item2Done
item3B:
cp 2
jr nz,item3C
ld hl,txtSelect2_3 ;action 3 for group B
jr item1Done
item3C:
ld hl,txtSelect3_3 ;action 3 for group C
item3Done:
bcall(_PutS)
bcall(_GetKey)
jp menuStart
quit: ;quit the program
bcall(_ClrLCDFull)
ret
;dispHeader
;
;displays the header centered and at the top
;
;Inputs: HL points to null-terminating string
;
;Output: text displayed, with the current group in inverse text
;
;Destroyed: a,de,hl
;
;Note: text string must be large text and take up the full line
;(use blank spaces to fill in gaps)
;
dispHeader: ;displays the header centered and at the top
ld de,0
ld (curRow),de
ld a,b
cp 1
jr nz,dispHeader1
set textInverse,(IY+TextFlags)
dispHeader1: ;group A
bcall(_PutS)
res textInverse,(IY+TextFlags)
bcall(_PutS)
cp 2
jr nz,dispHeader2
set textInverse,(IY+TextFlags)
dispHeader2: ;group B
bcall(_PutS)
res textInverse,(IY+TextFlags)
bcall(_PutS)
cp 3
jr nz,dispHeader3
set textInverse,(IY+TextFlags)
dispHeader3: ;group C
bcall(_PutS)
res textInverse,(IY+TextFlags)
ld hl,0
ld (curRow),hl
ret
;dispItems
;
;displays menu items at the start of the next line
;
;Inputs: HL points to null-terminating string
;
;Output: text displayed
;
;Destroyed: all
;
dispItems: ;displays menu items at the start of the next line
push bc
push hl
bcall(_NewLine)
pop hl
pop bc
bcall(_PutS)
djnz dispItems
ret
;curDraw
;
;Draws the cursor
;
;Inputs: C holds the highlighted item
;
;Outputs: Cursor displayed
;
;Destroyed: A
;
curDraw:
set textInverse,(IY+TextFlags) ;set inverse text
xor a
ld (curCol),a
ld a,c
ld (curRow),a
add a,$30 ;Character offset
bcall(_PutC)
ld a,':'
bcall(_PutC)
res textInverse,(IY+TextFlags)
ret
;curErase
;
;Erase the cursor
;
;Inputs: C highlighted item
;
;Ouputs: Cursor erased
;
;Destroyed: A
;
curErase:
xor a
ld (curCol),a
ld a,c
ld (curRow),a
add a,$30 ;Character offset
bcall(_PutC)
ld a,':'
bcall(_PutC)
ret
;========================================
;data
;========================================
txtHeader:
.db "GA",0
.db " ",0
.db "GB",0
.db " ",0
.db "GC",0
txtItem1_1:
.db "1:A1",0
txtItem1_2:
.db "2:A2",0
txtItem1_3:
.db "3:A3",0
txtItem2_1:
.db "1:B1",0
txtItem2_2:
.db "2:B2",0
txtItem2_3:
.db "3:B3",0
txtItem3_1:
.db "1:C1",0
txtItem3_2:
.db "2:C2",0
txtItem3_3:
.db "3:C3",0
txtSelect1_1:
.db "You selected A1",0
txtSelect1_2:
.db "You selected A2",0
txtSelect1_3:
.db "You selected A3",0
txtSelect2_1:
.db "You selected B1",0
txtSelect2_2:
.db "You selected B2",0
txtSelect2_3:
.db "You selected B3",0
txtSelect3_1:
.db "You selected C1",0
txtSelect3_2:
.db "You selected C2",0
txtSelect3_3:
.db "You selected C3",0
txtItemQuit:
.db "4:Quit",0
Scrolling menus
What if you have more items than will fit in one screen? A solution to this is to display items on the screen and then when the user scrolls past the limits of the screen, it will "move" the items up and display the other items that wouldn't fit.
Summary
There are so many variations of a menu interface that showing them all would be impractical and impossible. Use your imagination and come up with variations, like displaying pictures in the background, having a custom cursor, or anything else you can think of.
