Pl2 LINEA.DOC
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CHAPTER NR°8:
THE LINEAS
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*** INTRODUCTION ***
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- LineAs are graphical functions, they are very simple
but have the advantage of being really very fast.
(Much more than the VDI...)
LineAs are commands of the 'BLITTER', i.e., it is the HARDWARE
(Some PHYSICAL components of the computer and the routines that
are executed by the PROCESSOR himself.) that execute these func-
tions and not the SOFTWARE (The SOFTWARE part of your computer:
ROM, programs...).
If your ST is equipped with the BLITTER of course... (The MEGA 2ST and the
MEGA 4ST are equipped.)
NB: There is a SOFTWARE version of the BLITTER that is available in the public
--- domain in the form of a desktop accessory...
These functions are very fast since not coming from the SOFTWARE, the
routines do not need to be interpreted by the PROCESSOR.
- To call the LineAs functions, you will have to provide the appro-
priate parameters in the VDI TABLE and also in an INTERNAL TABLE
specific to LineAs.
Some registers will also be used.
Indeed, the LineAs use the VDI's CONTROL, PTSIN, PTSOUT,
INTIN, and INTOUT arrays.
Registers d0, d1, d2, a0, a1, a2 will also be used, so you will have
to be careful not to lose their content...
Some parameters are also provided by the LineAs in return in
d0, a0 or INTOUT (here again, be careful not to lose d0!)
We have seen that the LineAs use an INTERNAL TABLE:
It is in this table that the functions search for the parameters
that we have deposited, the only problem is that the location of this
internal table varies (hence its name).
To find the location of this internal table, just
call the function $A000 with:
DC.W $A000
What a strange syntax isn't it??
The explanation is very simple: During the ASSEMBLY step of your
listing, the ASCII codes representing the instructions and their operands
will be translated into BINARY because the 68000 only recognizes
information coded in binary:
Thus, a NOP will be translated by %100111001110001, a RTS by %0100111
001110101 etc... and so for all instructions.
If we translate these codes from binary to HEXADECIMAL, we obtain
instructions coded in HEX:
Thus, NOP will be written: $4E71
and RTS will be written: $4E75
etc...
However,
--
You can REPLACE, in an ASSEMBLER program, an instruction
by its HEX CODE equivalent if it is declared as such in
the TEXT segment, it would suffice to write:
DC.W $4E71 instead of a NOP (or DC.B $4E, $71)
or
DC.W $4E75 instead of an RTS ... (or DC.B $4E, $75)
This remains valid for all the instructions of the 68000 (Even for
labels).
But,
----
No 68000 instruction will be coded in HEX by a WORD of type:
$A... (or $F...)
We have therefore filled this lack (we rather took advantage of it!) by coding
the LineAs functions in $A...
NB: There are also $F... routines but we will not use them
-- because they are not compatible between the OLD ROM and NEW ROM versions
of the ST.
It will therefore suffice to write DC.W $A... for the 68000 to decode this
instruction by the LineA instruction of code $A...
There are a total of 16 commands that are installed and that can
be translated this way, these are the 16 LineAs routines:
To call them simply DECLARE them in the TEXT segment:
The LineAs:
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$A000: Installs the internal table
$A001: Places 1 point on the screen
$A002: Sets the color of a screen point
$A003: Draws an arbitrary line
$A004: Draws a horizontal line
$A005: Draws a filled rectangle
$A006: Draws a filled polygon
$A007: ?
$A008: Allows text block transfer
$A009: Activates the mouse cursor
$A00A: Deactivates the mouse cursor
$A00B: Modifies the shape of the mouse cursor
$A00C: Erases a sprite
$A00D: Draws a sprite
$A00E: Copies a block of points
$A00F: Identical to VDI's CONTOUR FILL function (opcode=103)
But let's now focus on our $A000 function:
We have seen earlier that it initializes the INTERNAL TABLE in which we will place parameters. This TABLE contains 50 variables, some the size of a word and some the size of a long word. To obtain the address where the table begins, we use the function $A000:
DC.W $A000
The function provides us with the address where the table is located in A0:
We can now access all the variables in this table using an INDIRECT addressing mode. However, since the variables do not all have the same size (word or long word), the (a0)+ and (a0) addressing modes will not be used...
We will use the d(a0) addressing mode to access the different parameters of the table:
So, MOVE.W 0(a0) will place the word=0 in the 1st parameter of the table,
MOVE.W 2(a0) will place the word=0 in the parameter at a0+2,
and so on...
Therefore, we need to know the values of the relative locations of the variables in the table. Since the d(a0) syntax is not very informative, we will define (with EQU) the relative locations of all these variables:
Here they are:
; Definition of EQUIVALENCES for the INTERNAL TABLE of LineAs
; Variable NAME = Relative Displacement
v_planes EQU 0 ;number of planes
v_lin_wr EQU 2 ;bytes per write line
ticontrol EQU 4 ;address of T.I CONTROL
tiintin EQU 8 ;address of T.I INTIN
tiptsin EQU 12 ;address of T.I PTSIN
tiintout EQU 16 ;address of T.I INTOUT
tiptsout EQU 20 ;address of T.T PTSOUT
_fg_bp_1 EQU 24 ;bit 0 of color
_fg_bp_2 EQU 26 ;bit 1 of color
_fg_bp_3 EQU 28 ;bit 2 of color
_fg_bp_4 EQU 30 ;bit 3 of color
_lstlin EQU 32 ;always =-1
_ln_mask EQU 34 ;line shape for $A003
_wrt_mode EQU 36 ;WRITE MODE
_x1 EQU 38 ;X coordinate of the first point
_y1 EQU 40 ;Y coordinate of the first point
_x2 EQU 42 ;X coordinate of the second point
_y2 EQU 44 ;Y coordinate of the second point
_patptr EQU 46 ;fill address
_patmsk EQU 50 ;fill number
_multifill EQU 52 ;details later
_clip EQU 54 ;clipping flag
_xmn_clip EQU 56 ;leftmost X for clipping
_ymn_clip EQU 58 ;highest Y for clipping
_xmx_clip EQU 60 ;rightmost X for clipping
_ymx_clip EQU 62 ;lowest Y for clipping
_xacc_dda EQU 64 ;points to $8000 for TXTBLT
_dda_inc EQU 66 ;enlargement factor=$FFFF
_t_sclsts EQU 68 ;=0
_mono_status EQU 70 ;TEXT EFFECTS type
_sourcex EQU 72 ;character number in SET
_sourcey EQU 74 ;=0
_destx EQU 76 ;X coordinate of TEXT
_desty EQU 78 ;Y coordinate of TEXT
_delx EQU 80 ;character width
_dely EQU 82 ;character height
_fbase EQU 84 ;SET address
_fwidth EQU 88 ;SET X
_style EQU 90 ;FLAG for TEXT EFFECTS
_litemark EQU 92 ;shading mask
_skewmask EQU 94 ;TEXT inclination mask
_weight EQU 96 ;number of enlargement bits
_r_off EQU 98 ;offset for TEXT italic
_l_off EQU 100 ;left (Left) offset
_scale EQU 102 ;enlargement flag (1/0)
_chup EQU 104 ;TEXT rotation angle
_txt_fg EQU
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