source: buchla-68k/vlib/vcputs.s@ 109c83b

Last change on this file since 109c83b was 109c83b, checked in by Thomas Lopatic <thomas@…>, 7 years ago

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Line 
1* ------------------------------------------------------------------------------
2* vcputs.s -- output a character string to a 4-bit per pixel graphics window
3* Version 3 -- 1987-07-31 -- D.N. Lynx Crowe
4* (c) Copyright 1987 -- D.N. Lynx Crowe
5* ------------------------------------------------------------------------------
6*
7* vcputs(obase, nw, fg, bg, row, col, str)
8* int *obase, nw, fg, bg, row, col;
9* char *str;
10*
11* Outputs characters from the string at 'str' to an 'nw'
12* character wide 4-bit per pixel graphics window at 'obase'
13* at ('row','col'), using 'fg' as the foreground color, and
14* 'bg' as the background color. Uses cgtable[][256] as the
15* VSDD formatted character generator table.
16* No error checks are done.
17*
18* ------------------------------------------------------------------------------
19 .text
20*
21 .xdef _vcputs
22*
23 .xref _cgtable
24*
25* Argument offsets from a6:
26*
27OBASE .equ 8 * Output area base address
28NW .equ 12 * Character width of output area
29FG .equ 14 * Foreground color
30BG .equ 16 * Background color
31ROW .equ 18 * Row
32COL .equ 20 * Column
33STR .equ 22 * String base address
34*
35* Program constant definitions:
36*
37HPIX .equ 8 * Character width in pixels
38VPIX .equ 12 * Character height in pixels
39HCW .equ 4 * Horizontal character width (bytes)
40PSHIFT .equ 12 * Pixel shift into MS bits
41HSHIFT .equ 4 * Pixel right shift
42*
43 .page
44*
45* Register usage:
46*
47* d0 output word and scratch
48* d1 CG word and scratch
49* d2 pixel counter
50*
51* d3 foreground color (in the 4 ms bits)
52* d4 background color (in the 4 ms bits)
53* d5 width of the area in bytes
54* d6 scan line counter
55*
56* a0 CG table pointer
57* a1 output area scan line pointer
58* a2 input string character pointer
59*
60* a3 output area character base pointer
61*
62 .page
63*
64_vcputs: link a6,#0 * Link stack frames
65 movem.l d3-d6/a3,-(a7) * Save registers we use
66 move.w #PSHIFT,d1 * Set shift constant
67 move.w FG(a6),d3 * Setup foreground color
68 lsl.w d1,d3 * ... in ms 4 bits of d3.W
69 move.w BG(a6),d4 * Setup background color
70 lsl.w d1,d4 * ... in ms 4 bits of d4.W
71 move.w NW(a6),d5 * Get line width in d5.W
72 lsl.w #2,d5 * Multiply width by 4 for offset
73 move.w ROW(a6),d0 * Calculate output address
74 move.w #VPIX,d1 * ... VPIX
75 mulu d1,d0 * ... * ROW
76 add.w #VPIX-1,d0 * ... + VPIX-1
77 mulu d5,d0 * ... * NW
78 clr.l d1 * ...
79 move.w COL(a6),d1 * ... +
80 lsl.w #2,d1 * ... COL * 4
81 add.l d1,d0 * ...
82 add.l OBASE(a6),d0 * ... + OBASE
83 movea.l d0,a3 * Leave output address in a3
84 movea.l STR(a6),a2 * Put string address in a2
85*
86cgl0: clr.l d0 * Clear out upper bits of d0
87 move.b (a2)+,d0 * Get next character
88 beq cgl5 * Done if character EQ 0
89*
90 movea.l a3,a1 * Establish output pointer in a1
91 adda.l #HCW,a3 * Update output pointer for next char.
92 lea _cgtable,a0 * Establish CG pointer in a0
93 lsl.w #1,d0 * ... 2 * character
94 adda.w d0,a0 * ... + _cgtable address
95 move.w #VPIX-1,d6 * Set scan line counter in d6
96*
97 .page
98cgl1: move.w (a0),d1 * Get character generator word in d1
99 move.w #(HPIX/2)-1,d2 * Set pixel counter in d2
100*
101cgl2: lsr.w #HSHIFT,d0 * Shift output word right 1 pixel
102 btst.l #0,d1 * Check CG word ls bit
103 beq cgl3 * Set background color if bit EQ 0
104*
105 or.w d3,d0 * OR foreground color into output word
106 bra cgl4 * Go update CG word
107*
108cgl3: or.w d4,d0 * OR background color into output word
109*
110cgl4: lsr.w #1,d1 * Shift CG word right 1 pixel
111 dbf d2,cgl2 * Loop for first 4 pixels
112*
113 move.w d0,(a1)+ * Store first output word in scan line
114 move.w #(HPIX/2)-1,d2 * Set pixel counter in d2
115*
116cgl2a: lsr.w #HSHIFT,d0 * Shift output word right 1 pixel
117 btst.l #0,d1 * Check CG word ls bit
118 beq cgl3a * Set background color if bit EQ 0
119*
120 or.w d3,d0 * OR foreground color into output word
121 bra cgl4a * Go update CG word
122*
123cgl3a: or.w d4,d0 * OR background color into output word
124*
125cgl4a: lsr.w #1,d1 * Shift CG word right 1 pixel
126 dbf d2,cgl2a * Loop for last 4 pixels
127*
128 move.w d0,(a1) * Store second output word in scan line
129 suba.w d5,a1 * Update output pointer
130 suba.w #2,a1 * ...
131 adda.l #512,a0 * Update CG pointer for next scan line
132 dbf d6,cgl1 * Loop for all scan lines
133*
134 bra cgl0 * Loop for next character
135*
136cgl5: movem.l (a7)+,d3-d6/a3 * Restore registers
137 unlk a6 * Unlink stack frames
138 rts * Return to caller
139*
140 .end
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