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starfield/main.asm

@@ -5,12 +5,6 @@ org $7530
 tv_flag     EQU $5c3c   ; TV flags
 last_k      EQU $5c08   ; Last pressed key
 clr_screen  EQU $0daf   ; ROM routine to clear the screen
-frames      EQU $5c78
-
-; Video RAM
-LINHA9      EQU $4820
-LINHA10     EQU $4840
-LINHA11     EQU $4860   
 
 ; Star Structure
 ; X - 1 Byte - $00 - $ff
@@ -19,7 +13,6 @@ LINHA11     EQU $4860
 ; Color - 1 Byte
 STAR_SIZE   EQU $4
 MAX_STARS   EQU 10
-;STARS       DS STAR_SIZE * MAX_STARS, 0
 
 INCLUDE "starrnd.asm"
 
@@ -30,21 +23,21 @@ start
 
     call clear_screen
 
-    ld de, StarRnd
+    ld hl, StarRnd
     ld c, MAX_STARS
 main
     push bc
-    ld a, (de)
-    ld c, a
-    inc de
-    ld a, (de)
-    ld b, a
-    call Get_Pixel_Address
     ld a, (hl)
+    ld d, a
+    inc hl
+    ld a, (hl)
+    ld e, a
+    call calculate_screen_address
+    ld a, (de)
     set 0, a
-    ld (hl), a
+    ld (de), a
     pop bc
-    inc de
+    inc hl
     dec c
     jr nz, main
     
@@ -52,34 +45,51 @@ main
     ret
 
 PROC
-; Get screen address
+;Input:
-; B = Y pixel position
+; D = Y Coordinate
-; C = X pixel position
+; E = X Coordinate
-; Returns address in HL
+;
-Get_Pixel_Address
+;Output:
-    ld a,b          ; Calculate Y2,Y1,Y0
+; DE = Screen Address
-    and %00000111   ; Mask out unwanted bits
+;
-    or %01000000    ; Set base address of screen
+calculate_screen_address
-    ld h, a         ; Store in H
+    ld a,d
-    ld a, b         ; Calculate Y7,Y6
-    rra             ; Shift to position
-    rra
-    rra
-    and %00011000   ; Mask out unwanted bits
-    or h            ; OR with Y2,Y1,Y0
-    ld h, a         ; Store in H
-    ld a, b         ; Calculate Y5,Y4,Y3
-    rla             ; Shift to position
     rla
-    and %11100000   ; Mask out unwanted bits
+    rla
-    ld l, a         ; Store in L
+    and 224
-    ld a, c         ; Calculate X4,X3,X2,X1,X0
+    or e
-    rra             ; Shift into position
+    ld e,a
+    ld a,d
     rra
     rra
-    and %00011111   ; Mask out unwanted bits
+    or 128
-    or l            ; OR with Y5,Y4,Y3
+    rra
-    ld l, a         ; Store in L
+    xor d
+    and 248
+    xor d
+    ld d,a
+    ret
+ENDP
+
+PROC
+;Input:
+; DE = Current screen address
+;
+;Output:
+; DE = (Y + 1) screen address
+;
+increment_y
+    inc d
+    ld a,d
+    and 7
+    ret nz
+    ld a,e
+    add a,32
+    ld e,a
+    ret c
+    ld a,d
+    sub 8
+    ld d,a
     ret
 ENDP
 

starfield/stargen.py

@@ -16,7 +16,7 @@ for x in range(NumStars):
     x = random.randint(0,256 - 1)
     y = random.randint(0,192 - 1)
     #z = random.randint(0,10)
-    #f.write("\t\tdb %i, %i, %i\n" % (x ,y ,z))
+    #f.write("\t\tdb %i, %i, %i\n" % (y ,x ,z))
     f.write("\t\tdb %i, %i\n" % (y ,x))
 
 f.close()

starfield/starrnd.asm

@@ -1,11 +1,11 @@
 StarRnd
-		db 16, 61
+		db 68, 103
-		db 146, 24
+		db 121, 245
-		db 77, 8
+		db 158, 242
-		db 131, 131
+		db 62, 46
-		db 138, 154
+		db 149, 245
-		db 52, 4
+		db 138, 234
-		db 108, 162
+		db 145, 123
-		db 58, 94
+		db 137, 96
-		db 127, 101
+		db 45, 226
-		db 144, 6
+		db 30, 97