Bit block transfer

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6.13 Text block transfer

Name:

»Text block transfer«

Line-A number:

$A008

Syntax:

Bindings für text_blt

Description:

This Line-A function outputs a single character. The source for the character must have the same buildup as in a GDOS raster font. One can can regard the font data as a large image, whose height corresponds to the character height. All characters lie close to each other in this "image". Additionally a GDOS font contains an offset table, containing the offset for each character in this large image. The parameter ade_lo of the font header contains the first ASCII character for which an image and thus also an offset is present. This offset is to be passed together with the font data to this Line-A function. The Y-offset is usually 0. As Line-A does not manage the fonts itself and also does not know the font header, corresponding parameters for the font data have to be passed. To this must be added a string of other parameters for various effects such as italic..., for instance. The following Line-A variables are used:

Variable

Meaning

wrt_mode

Writing mode, the following are possible:

REPLACE 0	Replace
TRANS 1	Transparent (OR)
XOR 2	Inverse (XOR)
INVERS 3	Inverse Transparent (XOR with not(LN_MASK))

xacc_dda

Should be set at each call to $8000

dda_inc

Scaling factor

t_sclsts

Scaling direction, i.e. whether one is enlarging or reducing

mono_status

1 if all characters have the same width, i.e. we are dealing with a non-proprtional font, else 0

sourcex

X-coordinate of the character in font to be output; can be obtained from the offset table

sourcey

Y-coordinate of the character in the font, normally 0

destx

X-coordinate of the screen position at which the character is to be output

desty

Y-coordinate of the screen position at which the character is to be output

delx

Width of the character, can also be obtained from the font header

dely

Height of the character, can also be obtained from the font header

fbase

The pointer to the font data, i.e. the image of the glyph

fwidth

Width of the font image

style

Specifies the text effects; individual bits represent individual effects and may be combined:

Bit 0	Bold
Bit 1	Light
Bit 2	Skewed ("italics")
Bit 3	Underlined (is ignored)
Bit 4	Outlined

litemask

A mask for light

skewmask

A mask for skewed

weight

The width for bold

r_off

The right offset for skewed, so more or less a parameter for the "slope" of the character

l_off

The left offset for skewed, so more or less a parameter for the "slope" of the character

scale

1, if scaling is desired

chup

Rotation angle in 1/10 degree; however, only rotation of multiples of 90 degrees are possible, i.e. values 0, 900, 1800, 2700

text_fg

Text colour

text_bg

Background colour

scrtchp

A buffer that should offer twice as much space as occupied by the character, so that Line-A can calculate the text effects

scrpt2

An index into the buffer that points to the centre of the buffer, i.e. specifies half of the bufer size

clip

1 if clipping is desired, else 0

xmn_clip

X-coordinate of the top left corner of the clipping region, if clipping is switched on

ymn_clip

Y-coordinate of the top left corner of the clipping region, if clipping is switched on

xmx_clip

X-coordinate of the bottom right corner of the clipping region, if clipping is switched on

ymx_clip

Y-coordinate of the bottom right corner of the clipping region, if clipping is switched on

The binding from TC passes a pointer to the font header, flags for scaling, style, rotation vector, foreground and background colour not to the text_blt function, but uses the separate function set_text_blt for setting the parameters in the Line-A parameter block. Data about the font are set automatically.

Return value:

The function does not return a result.

Availability:

All TOS versions.

6.13.1 Bindings for text_blt

Pure-C:

void text_blt( int16_t x, int16_t y, uint8_t c );

Assembler:

; Save registers
movem.l   D0-D2/A0-A2,-(A7)
; Pointer parameter block LINEA
move.l    pParamblk,A0
; Writing mode in LINEA.wrt_mode
move.w    wmode,(36,A0)
; Clip mode in LINEA.clip
move.w    mode,(54,A0)
; Top left clip corner, X-coordinate in LINEA.xmn_clip
move.w    cx1,(56,A0)
; Top left clip corner, Y-coordinate in LINEA.ymn_clip
move.w    cy1,(58,A0)
; Bottom right clip corner, X-coordinate in LINEA.xmx_clip
move.w    cx2,(60,A0)
; Bottom right clip corner, Y-coordinate in LINEA.ymx_clip
move.w    cy2,(62,A0)
; Put $8000 in xacc_dda
move.w    #$8000,(64,A0)
; Scaling factor in LINEA.dda_inc
move.w    dda_inc,(66,A0)
; Scaling direction in LINEA.t_sclsts
move.w    t_sclsts,(68,A0)
; Proportional font in LINEA.mono_status
move.w    mono_status,(70,A0)
; X-coordinate in font in LINEA.sourcex
move.w    sourcex,(72,A0)
; Y-coordinate in font in LINEA.sourcey
move.w    sourcey,(74,A0)
; X-destination coordinate LINEA.destx
move.w    destx,(76,A0)
; Y-destination coordinate in LINEA.desty
move.w    desty,(78,A0)
; Width of the character in LINEA.delx
move.w    delx,(80,A0)
; Height of the character LINEA.dely
move.w    dely,(82,A0)
; Start of font data in LINEA.fbase
move.l    fbase,(84,A0)
; Width of the font image in LINEA.fwidth
move.w    fwidth,(88,A0)
; Write style in LINEA.style
move.w    style,(90,A0)
; Mask for light in LINEA.litemask
move.w    litemask,(92,A0)
; Mask for skewed in LINEA.skewmask
move.w    skewmask,(94,A0)
; Width for bold in LINEA.weight
move.w    weight,(96,A0)
; Skewed offset right in LINEA.r_off
move.w    r_off,(98,A0)
; Skewed offset left in LINEA.l_off
move.w    l_off,(100,A0)
; VScaling yes/no in LINEA.scale
move.w    scale,(102,A0)
; Rotation angle in LINEA.chup
move.w    chup,(104,A0)
; Text color LINEA.text_fg
move.w    text_fg,(106,A0)
; Buffer in LINEA.scrtchp
move.l    scrtchp,(108,A0)
; Index to mid-buffer in LINEA.scrpt2
move.w    scrpt2,(112,A0)
; Background color in LINEA.text_bg
move.w    text_bg,(114,A0)
; Line-A opcode
dc.w      $A008
; Restore registers
movem.l   (A7)+,D0-D2/A0-A2

Line-A

Bit block transfer

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