LINE-A

Overview

The Line-A portion of the operating system is so named because it uses a special exception vector of 680x0 processors triggered when the first nibble of the a command word is $A. On Atari systems this vector is routed to the operating system ROMs and provides a low-level yet high-speed graphics interface.

The Line-A system is included in this document for completeness only. It is recommended that its use be avoided and that the counterpart VDI calls be used instead. Atari has not guaranteed that it will maintain Line-A compatibility in future systems. Its functionality has already been limited as video capabilities have advanced beyond its design.

The Line-A Variable Table

The Line-A opcode $A000 will return a pointer to an internal variable table in D0 and A0. This table is used by the Line-A functions as a parameter passing mechanism as opposed to using the stack or internal registers.

Members of the Line-A variable table are accessed via offsets from the base address. The function, location, and size of documented variables are as follows:

Name	Offset	Size	Contents
RESERVED	-910	LONG	Reserved for future use.
CUR_FONT	-906	LONG	Pointer to the current font header.
RESERVED	-902	92 BYTEs	Reserved for future use.
M_POS_HX	-856	WORD	X Offset into the mouse form of the 'hot spot'.
M_POS_HY	-854	WORD	Y Offset into the mouse form of the 'hot spot'.
M_PLANES	-852	WORD	Writing mode for the mouse pointer (1 = VDI Mode, -1 = XOR Mode). Defaults to VDI mode.
M_CDB_BG	-850	WORD	Mouse pointer background color.
M_CDB_FG	-848	WORD	Mouse pointer foreground color.
MASK_FORM	-846	32 WORDs	Image and Mask for the mouse pointer. Data is stored in the following format: Line 0 Mask Line 0 Image Line 1 Mask Line 1 Image etc.
INQ_TAB	-782	46 WORDs	This area contains 45 WORDs of information returned from a vq_extnd() of the physical screen workstation plus one extra reserved WORD.
DEV_TAB	-692	46 WORDs	This area contains the first 45 WORDs of information returned from a v_opnwk() of the physical screen workstation plus one extra reserved WORD.
GCURX	-602	WORD	Current mouse pointer X position.
GCURY	-600	WORD	Current mouse pointer Y position.
M_HID_CT	-598	WORD	Current mouse 'hide' count (number of times mouse has been hidden, 0 = visible).
MOUSE_BT	-596	WORD	Bitmap of the current mouse button status.
REQ_COL	-594	48 WORDs	Contains 48 WORDs of RGB data for the first 16 VDI color registers as would be returned by vq_color().
SIZ_TAB	-498	15 WORDs	This table contains the final 12 WORDs of information returned from a v_opnwk() of the physical screen workstation plus 3 reserved WORDs.
RESERVED	-468	WORD	Reserved for future use.
RESERVED	-466	WORD	Reserved for future use.
CUR_WORK	-464	LONG	Pointer to the current VDI workstation attribute table.
DEF_FONT	-460	LONG	Pointer to the default font header.
FONT_RING	-456	4 LONGs	This area contains three pointers and a NULL. The first two pointers point to linked lists of system font headers. The third pointer points to the linked list of GDOS based fonts.
FONT_COUNT	-440	WORD	Total number of fonts pointed to by the FONT_RING pointers.
RESERVED	-438	90 BYTEs	Reserved for future use.
CUR_MS_STAT	-348	BYTE	Bitmap of mouse status since the last interrupt as follows: Bit Meaning 0 Left mouse status (0=up) 1 Right mouse status (0=up) 2 Reserved 3 Reserved 4 Reserved 5 Mouse move flag (1=moved) 6 Right mouse status flag (0=hasn't changed) 7 Left mouse status flag (0=hasn't changed)
RESERVED	-347	BYTE	Reserved for future use.
V_HID_CNT	-346	WORD	Number of times the text cursor has been hidden (0 = visible).
CUR_X	-344	WORD	X position where mouse pointer will be drawn.
CUR_Y	-342	WORD	Y position where mouse pointer will be drawn.
CUR_FLAG	-340	BYTE	Mouse redraw flag (if non-zero, mouse pointer will be redrawn at the next vertical blank interrupt).
MOUSE_FLAG	-339	BYTE	Mouse interrupt flag (0=disable interrupts)
RESERVED	-338	LONG	Reserved for future use.
V_SAV_XY	-334	2 WORDs	X and Y position of the text cursor as saved by the VT-52 emulator.
SAVE_LEN	-330	WORD	Height of the form saved in SAVE_AREA in pixels.
SAVE_ADDR	-328	LONG	Address of the first WORD of screen data contained in SAVE_AREA.
SAVE_STAT	-324	LONG	Save status flag as follows: Bit Meaning 0 Save buffer valid? (0=no) 1 Width of save (0=16 bits, 1=32 bits)
SAVE_AREA	-322	256 BYTEs	Save buffer for the mouse pointer,
USER_TIM	-66	LONG	Pointer to a routine which occurs at each timer tick. (use vex_timv() instead). Routine ends by jumping to function pointed to by NEXT_TIM.
NEXT_TIM	-62	LONG	See above.
USER_BUT	-58	LONG	Pointer to a routine called each time a mouse button is pressed (use vex_butv() instead).
USER_CUR	-54	LONG	Pointer to a routine called each time the mouse needs to be rendered (use vex_curv() instead).
USER_MOT	-50	LONG	Pointer to routine called each time the mouse is moved (use vex_motv() instead).
V_CEL_HT	-46	WORD	Current text cell height.
V_CEL_MX	-44	WORD	Number of text columns - 1.
V_CEL_MY	-42	WORD	Number of text rows - 1.
V_CEL_WR	-40	WORD	Number of bytes between character cells.
V_COL_BG	-38	WORD	Text background color.
V_COL_FG	-36	WORD	Text foreground color.
V_CUR_AD	-34	LONG	Text cursor physical address.
V_CUR_OF	-30	WORD	Offset (in bytes) from physical screen address to the top of the first text character.
V_CUR_XY	-28	2 WORDs	X and Y character position of the text cursor.
V_PERIOD	-24	BYTE	Current cursor blink rate.
V_CUR_CT	-23	BYTE	Countdown timer to next blink.
V_FNT_AD	-22	LONG	Pointer to system font data (monospaced).
V_FNT_ND	-18	WORD	Last ASCII character in font.
V_FNT_ST	-16	WORD	First ASCII character in font.
V_FNT_WD	-14	WORD	Width of the system font form in bytes.
V_REZ_HZ	-12	WORD	Horizontal pixel resolution.
V_OFF_AD	-10	LONG	Pointer to font offset table.
RESERVED	-6	WORD	Reserved for future use.
V_REZ_VT	-4	WORD	Vertical pixel resolution.
BYTES_LIN	-2	WORD	Bytes per screen line.
PLANES	0	WORD	Number of planes in the current resolution.
WIDTH	2	WORD	Width of the destination form in bytes.
CONTRL	4	LONG	Pointer to the CONTRL array.
INTIN	8	LONG	Pointer to the INTIN array.
PTSIN	12	LONG	Pointer to the PTSIN array.
INTOUT	16	LONG	Pointer to the INTOUT array.
PTSOUT	20	LONG	Pointer to the PTSOUT array.
COLBIT0	24	WORD	Color bit value used for plane 0.
COLBIT1	26	WORD	Color bit value used for plane 1.
COLBIT2	28	WORD	Color bit value used for plane 2.
COLBIT3	30	WORD	Color bit value used for plane 3.
LSTLIN	32	WORD	Last pixel draw flag (0=draw, 1=don't draw). Used to prevent the last pixel in a polyline segment drawn in XOR mode from overwriting the first pixel in the next line.
LNMASK	34	WORD	Line draw pattern mask.
WMODE	36	WORD	VDI writing mode.
X1	38	WORD	X coordinate for point 1.
Y1	40	WORD	Y coordinate for point 1.
X2	42	WORD	X coordinate for point 2.
Y2	44	WORD	Y coordinate for point 2.
PATPTR	46	LONG	Fill-pattern pointer.
PATMSK	50	WORD	This value is AND'ed with the value in Y1 to give an index into the current fill pattern for the current line.
MFILL	52	WORD	Multiplane fill pattern flag (0=Mono).
CLIP	54	WORD	Clipping flag (0=disabled).
XINCL	56	WORD	Left edge of clipping rectangle.
XMAXCL	58	WORD	Right edge of clipping rectangle.
YMINCL	60	WORD	Top edge of clipping rectangle.
YMAXCL	62	WORD	Bottom edge of clipping rectangle.
XDDA	64	WORD	Text scaling accumulator (set to $8000 prior to blitting text).
DDAINC	66	WORD	Scaling increment. If SIZE1 is the actual point size and SIZE2 is the desired point size then to scale up use:To scale down use:
SCALDIR	68	WORD	Text scaling direction (0=down, 1=up).
MONO	70	WORD	Monospaced font flag.
SOURCEX	72	WORD	X coordinate of character in font form.
SOURCEY	74	WORD	Y coordinate of character in font form.
DESTX	76	WORD	X position on screen to output character at.
DESTY	78	WORD	Y position on screen to output character at.
DELX	80	WORD	Width of the character to output.
DELY	82	WORD	Height of the character to output.
FBASE	84	LONG	Pointer to the font character image block.
FWIDTH	88	WORD	Width of the font form in bytes.
STYLE	90	WORD	Special effects flag bitmap as follows: Bit Meaning 0 Thickening 1 Lightening 2 Skewing 3 Underlining (not supported by Line-A) 4 Outlining
LITEMASK	92	WORD	Mask to lighten text (usually $5555).
SKEWMASK	94	WORD	Mask to skew text (usually $5555).
WEIGHT	96	WORD	Width to thicken characters by.
ROFF	98	WORD	Offset above baseline used for italicizing.
LOFF	100	WORD	Offset below baseline used for italicizing.
SCALE	102	WORD	Text scaling flag (0=no scale).
CHUP	104	WORD	Character rotation angle in tenths of degrees (supported only in 90 degree increments).
TEXTFG	106	WORD	Text foreground color.
SCRTCHP	108	LONG	Pointer to two contiguous scratch buffers used in creating text special effects.
SCRPT2	112	WORD	Offset from first buffer to second (in bytes).
TEXTBG	114	WORD	Text background color.
COPYTRAN	116	WORD	Copy raster mode (0=Opaque, 1=Transparent).
SEEDABORT	118	LONG	Pointer to a routine called by the seedfill routine at each line. If not needed during a seed fill you should point it to a routine like the following: seedabort: sub.l d0,d0 rts

Line-A Font Headers

Raster system and GDOS fonts are linked to form a list of font headers which contain the information needed to render text. Outline text generated by FSM is inaccessible in this manner.

Each monospaced font contains a font header, character and horizonatal offset table, and font form. All data types are in "Little Endian" (Intel format) and as such must be byte-swapped before use.

The font form is a raster form with each character laid side-by-side on the horizontal plane. The first character is WORD aligned but padding within the form only occurs at the end of a scanline to force the next scanline to be WORD aligned.

Each font header contains a pointer to the next font in the list. The list is terminated by a NULL pointer. The font header format is as follows:

Name	Offset	Type	Contents
font_id	0	WORD	Font ID number (must be unique).
point	2	WORD	Point size of font.
name	4	32 BYTEs	ASCII Name of font.
first_ade	36	UWORD	First ASCII character in font.
last_ade	38	UWORD	Last ASCII character in font.
top	40	UWORD	Distance from the top line of the font to the baseline.
ascent	42	UWORD	Distance from the ascent line of the font to the baseline.
half	44	UWORD	Distance from the half line of the font to the baseline.
descent	46	UWORD	Distance from the descent line of the font to the baseline.
bottom	48	UWORD	Distance from the bottom line of the font to the baseline.
max_char_width	50	UWORD	Width of the widest character in the font.
max_cell_width	52	UWORD	Width of the widest character cell in the font.
left_offset	54	UWORD	Amount character slants left when skewed.
right_offset	56	UWORD	Amount character slants right when skewed.
thicken	58	UWORD	Number of pixels to smear for thickening.
ul_size	60	UWORD	Size of an appropriate underline for the font.
lighten	62	UWORD	Mask for character lightening.
skew	64	UWORD	Mask for character skewing.
flags	66	UWORD	Font type flags.
hor_table	68	LONG	Pointer to the horizontal offset table. The horizontal offset table is an array of bytes with one entry per character denoting the pixel offset to the character.
off_table	72	LONG	Pointer to the character offset table. The character offset table is an array of WORDs with one entry per character denoting the byte offset into the font form of the character.
dat_table	76	LONG	Pointer to the character data.
form_width	80	UWORD	Width of the font form in bytes.
form_height	82	UWORD	Height of the font form in pixels.
next_font	84	LONG	Pointer to the next font in the list (0=no more fonts).
reserved	88	UWORD	Reserved for future use.

Line-A Function Calling Procedure