more screeen work, provided unofficial line clear routine

2020-01-03 20:43:32 +01:00
1 parent ca22b228d7
commit 64c8bc6b82
@@ -245,7 +245,7 @@ Not all of them - only these we want to have implemented.
 | `$E8DA`   | color code table             | DONE     |                                                    |
 | `$E8EA`   | scroll line                  | NOT DONE |                                                    |
 | `$E96C`   | insert line on top           | NOT DONE |                                                    |
-| `$E9FF`   | clear line                   | NOT DONE |                                                    |
+| `$E9FF`   | clear line                   | DONE     |                                                    |
 | `$EA31`   | default IRQ                  | PARTIAL  |                                                    |
 | `$EA7E`   | ack CIA1 + below             | DONE     |                                                    |
 | `$EA81`   | ret from IRQ/NMI             | DONE     |                                                    |
@@ -1,4 +0,0 @@
-
-// XXX provide documentation and implementation
-
-    STUB_IMPLEMENTATION()
@@ -3,9 +3,7 @@
 // CLR key handling within CHROUT
 //

-chrout_screen_CLR: /* YYY disabled for rework
+chrout_screen_CLR:

 	jsr clear_screen
 	jmp chrout_screen_done
-
-*/
@@ -4,12 +4,7 @@
 //


-chrout_screen_HOME:
-	rts
-
-/* YYY disabled for rework
 chrout_screen_HOME:

 	jsr cursor_home
 	jmp chrout_screen_done
-*/
@@ -4,13 +4,11 @@
 //


-chrout_screen_RETURN: /* YYY disabled for rework
+chrout_screen_RETURN:

 	// RETURN clears quote and insert modes, it also clears reverse flag
 	lda #$00
 	sta QTSW
 	sta INSRT
 	sta RVS
-	jmp chrout_screen_advance_to_next_line
-
-*/
+	jmp screen_advance_to_next_line
@@ -19,7 +19,7 @@ clear_screen_real:
 	dey
 	bpl !-

-	// YYY flow can probably be size-optimized, by clearing a single row each time (we will need such a subroutine)
+	// YYY flow can probably be size-optimized by calling screen_clear_line in a loop

 	// Clear screen character RAM. Unfortunately, the HIBASE value is not on the zero page,
 	// we will reuse PNT (it will be overridden in a moment nevertheless) as the pointer
@@ -9,7 +9,11 @@

 screen_calculate_PNT_USER:

-	// YYY jsr screen_normalize_xy - do we need this? probably not
+	ldx TBLX
+
+	// FALLTROUGH
+
+screen_calculate_PNT_USER_from_X: // entry point for screen_clear_line

 	// Reset pointer to start of screen

@@ -20,7 +24,7 @@ screen_calculate_PNT_USER:

 	// Add 40 to PNT for every line

-	ldx TBLX
+	cpx #$00	
 	beq screen_calculate_USER
 !:
 	lda #40
@@ -0,0 +1,34 @@
+
+//
+// Well-known routine, described in:
+//
+// - [CM64] Computes Mapping the Commodore 64 - page 219
+// - http://sta.c64.org/cbm64scrfunc.html
+//
+// input: .X - screen line to clear
+//
+// Checked that original routine preserves X (convenient for loops),
+// and leaves space screen code in .A, so duplicate this behaviour
+//
+
+
+screen_clear_line:
+
+	// First, calculate PNT and USER
+	phx_trash_a
+	jsr screen_calculate_PNT_USER_from_X
+	plx_trash_a
+
+	// Now clear the line
+	ldy #39
+!:
+	lda COLOR
+	sta (USER), y
+	lda #$20                           // space character screen code
+	sta (PNT), y
+
+	dey
+	bpl !-
+
+	// Done
+	rts
@@ -1,8 +1,8 @@


 screen_advance_to_next_line:
-.break
-	rts
+
+	jmp screen_advance_to_next_line

 /* YYY disabled for rework

@@ -6,8 +6,9 @@ screen_grow_logical_line_done:


 screen_grow_logical_line:
-.break
-	rts
+
+	jmp screen_grow_logical_line // YYY
+

 /* YYY disabled for rework