Add low-res Apple II graphics functions

Author: willisblackburn

apple2/apple2.inc

@@ -2,6 +2,8 @@
 ;
 ; SPDX-License-Identifier: MIT
 
+H2          := $2C
+V2          := $2D
 PROMPT      := $33      ; GETLN prompt character
 COUTMASK    := $50
 HIMEM       := $73      ; Highest available memory address+1
@@ -16,6 +18,13 @@ LCROM       := $C081    ; Select ROM
 LCROMWP     := $C082    ; Select ROM + write protect RAM
 LCRAM       := $C083    ; Select RAM (read twice to write-enable RAM)
 
+PLOT        := $F800
+HLINE       := $F819
+VLINE       := $F828
+CLRSCR      := $F832
+CLRTOP      := $F836
+SETCOL      := $F864
+SCRN        := $F871
 SETTXT      := $FB39
 PREAD       := $FB1E
 SETGR       := $FB40

apple2/apple2_extension_lc.s

@@ -7,38 +7,100 @@
 ex_statement_name_table:
         name_table_entry "GR"
 :       name_table_entry "TEXT"
+:       name_table_entry "HOME"
+:       name_table_entry "COLOR"
+            JUMP pvm_expression
+:       name_table_entry "PLOT"
+            JUMP pvm_arg_2
+:       name_table_entry "HLIN"
+            CALL pvm_arg_2
+            MATCH "AT"
+            JUMP pvm_expression
+:       name_table_entry "VLIN"
+            CALL pvm_arg_2
+            MATCH "AT"
+            JUMP pvm_expression
 :       name_table_end
 
 ex_function_name_table:
         name_table_entry "PDL"
+:       name_table_entry "SCRN"
 :       name_table_end
 
 .segment "XVEC"
 
 ex_statement_vectors:
-        .word   exec_gr-1
-        .word   exec_text-1
-
+        .word   SETGR-1
+        .word   SETTXT-1
+        .word   HOME-1
+        .word   exec_color-1
+        .word   exec_plot-1
+        .word   exec_hlin-1
+        .word   exec_vlin-1
+        
 .code
 
-exec_gr:
-        jsr     SETGR
-        rts
+exec_color:
+        jsr     evaluate_expression
+        jsr     pop_int_fp0             ; Pop the color value
+        jmp     SETCOL
+
+exec_plot:
+        jsr     evaluate_argument_list
+        jsr     pop_int_fp0             ; Pop the Y value
+        pha                             ; We'll move it into A later
+        jsr     pop_int_fp0             ; Pop the X value
+        tay                             ; Move X into Y for PLOT
+        pla                             ; Get back Y from stack into A
+        jmp     PLOT
+
+exec_hlin:
+        jsr     get_hlin_vlin_arguments
+        jmp     HLINE
 
-exec_text:
-        jsr     SETTXT
+exec_vlin:
+        jsr     get_hlin_vlin_arguments
+        jmp     VLINE
+
+get_hlin_vlin_arguments:
+        jsr     evaluate_argument_list  ; Evaluate start and end
+        inc     line_pos                ; Skip "AT"
+        inc     line_pos
+        jsr     evaluate_expression
+        jsr     pop_int_fp0             ; Get coordinate (Row for HLIN, Column for VLIN)
+        pha                             ; Save on hardware stack
+        jsr     pop_int_fp0             ; Get end point (H2/V2)
+        sta     H2
+        sta     V2
+        jsr     pop_int_fp0             ; Get start point
+        tay                             ; Start point into Y
+        pla                             ; Coordinate into A
         rts
 
 .segment "XFUNC"
 
 ex_function_table:
         .word   fun_pdl-1
         .byte   1 | PROLOG_POP_INT | EPILOG_PUSH_INT
+        .word   fun_scrn-1
+        .byte   2 | PROLOG_POP_INT | EPILOG_PUSH_INT
 
 .code
 
 fun_pdl:
+        jsr     pop_int_fp0             ; Get paddle index
+        tax
         jsr     PREAD                   ; Returns result in Y
         tya
         ldx     #0
         rts
+
+fun_scrn:
+        jsr     pop_int_fp0             ; Pop the Y value (second arg)
+        pha                             ; Save it
+        jsr     pop_int_fp0             ; Pop the X value (first arg)
+        tay                             ; Move X into Y
+        pla                             ; Get back Y into A
+        jsr     SCRN
+        ldx     #0                      ; Make sure high byte is 0
+        rts