viewport.asm

    ; extra MACRO files need to go here
    include "myMacros.inc"

    .assume adl=1                       ; ez80 ADL memory mode
    .org $40000                         ; load code here

    jp start_here                       ; jump to start of code

    .align 64                           ; MOS header
    .db "MOS",0,1     

start_here:
            
    push af                             ; store all the registers
    push bc
    push de
    push ix
    push iy

; ------------------
; This is our actual code

; prepare the screen

    SET_MODE 8                          ; mode 8 is 640x480 pixels, 64 colours


; Sending a VDU byte stream

    ld hl, VDUdata                      ; address of string to use
    ld bc, endVDUdata - VDUdata         ; length of string
    rst.lil $18                         ; Call the MOS API to send data to VDP 

    ld a, $08                           ; code to send to MOS
    rst.lil $08                         ; get IX pointer to System Variables

WAIT_HERE:                              ; loop here until we hit ESC key
    ld a, (ix + $05)                    ; get ASCII code of key pressed
    cp 27                               ; check if 27 (ascii code for ESC)   
    jp z, EXIT_HERE                     ; if pressed, jump to exit

    jr WAIT_HERE

; ------------------
; This is where we exit the program

EXIT_HERE:

    CLS 
    pop iy                              ; Pop all registers back from the stack
    pop ix
    pop de
    pop bc
    pop af
    ld hl,0                             ; Load the MOS API return code (0) for no errors.
    ret                                 ; Return to MOS

; ------------------
; This is the data we send to VDP

VDUdata:
    .db 23, 0, 192, 0                   ; set to non-scaled graphics

    .db 24                              ; set graphics viewport:-
    .dw 40, 150, 270, 40                ; 24, left; bottom; right; top;

    ; FOR A SINGLE PIXEL PLOT

    .db 18, 0, bright_red               ; set graphics colour: mode (0), colour

    .db 25, 69                          ; PLOT: mode (69 is a point in current colour),
    .dw 200,80                          ; X; Y;

    ; FOR A LINE

    .db 18, 0, bright_magenta           ; set graphics colour: mode (0), colour

    .db 25, 69                          ; PLOT: mode (69 is a point in current colour),
    .dw 300, 60                         ; X; Y;

    .db 25, 13                          ; PLOT: mode (13 is a line),
    .dw 250,130                         ; X; Y;

    ; FOR A RECTANGLE

    .db 18, 0, green                    ; set graphics colour: mode (0), colour

    .db 25, 69                          ; PLOT: mode (69 is a point in current colour),
    .dw 10,120                          ; X; Y;

    .db 25, 101                         ; PLOT: mode (101 is a filled rectangle),
    .dw 100,180                         ; X; Y;


   ; FOR A CIRCLE   

    .db 18, 0, bright_yellow            ; set graphics colour: mode (0), colour

    .db 25, 68                          ; PLOT: mode (69 is a MOVE TO but don't plot point),
    .dw 180,140                         ; X; Y;

    .db 25, 149                         ; PLOT: mode (149 is an outlined circle),
    .dw 200,160                         ; X; Y;

    ; FOR A FILLED TRIANGLE

    .db 18, 0, blue                     ; set graphics colour: mode (0), colour

    .db 25, 69                          ; PLOT: mode (69 is a point in current colour),
    .dw 10,10                           ; X; Y;

    .db 25, 69                          ; PLOT: mode (69 is a point in current colour),
    .dw 50, 100                         ; X; Y;

    .db 25, 85                          ; PLOT: mode (85 is a filled triangle),
    .dw 200,20                          ; X; Y;

endVDUdata:

; ------------------
; colour data

bright_red:     equ     9
green:          equ     2
bright_yellow:  equ     11
bright_magenta: equ     13
blue:           equ     4
white:          equ     7
black:          equ     0
bright_white:   equ     15