source: buchla-68k/vlib/tsplot4.s@ c65a0e2

Last change on this file since c65a0e2 was 109c83b, checked in by Thomas Lopatic <thomas@…>, 7 years ago

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1* ------------------------------------------------------------------------------
2* tsplot4.s -- output characters to a 4-bit / pixel graphics window
3* with variable vertical pitch
4* Version 1 -- 1987-08-04 -- D.N. Lynx Crowe
5* (c) Copyright 1987 -- D.N. Lynx Crowe
6* ------------------------------------------------------------------------------
7*
8* tsplot4(obase, nw, fg, row, col, str. pitch)
9* int *obase, nw, fg, row, col, pitch;
10* char *str;
11*
12* Outputs characters from the string at 'str' to an 'nw'
13* character wide 4-bit per pixel graphics window at 'obase'
14* at ('row','col'), using 'fg' as the foreground color.
15* Uses cgtable[][256] as the VSDD formatted character
16* generator table. Assumes 12 bit high characters in the
17* cgtable. Uses 'pitch' as the vertical spacing between
18* character rows. No error checks are done.
19* The string must fit the output area (no overlaps, single line).
20*
21* ------------------------------------------------------------------------------
22 .text
23*
24 .xdef _tsplot4
25*
26 .xref _cgtable
27*
28* Argument offsets from a6:
29*
30OBASE .equ 8 * LONG - Output area base address
31NW .equ 12 * WORD - Character width of output area
32FG .equ 14 * WORD - Foreground color
33ROW .equ 16 * WORD - Row
34COL .equ 18 * WORD - Column
35STR .equ 20 * LONG - String base address
36PITCH .equ 24 * WORD - Vertical spacing between rows
37*
38* Program constant definitions:
39*
40HPIX .equ 8 * Character width in pixels
41VPIX .equ 12 * Character height in pixels
42HCW .equ 4 * Horizontal character width (bytes)
43PSHIFT .equ 12 * Pixel shift into MS bits
44HSHIFT .equ 4 * Pixel right shift
45*
46 .page
47*
48* Register usage:
49*
50* d0 output word and scratch
51* d1 CG word and scratch
52* d2 pixel counter
53*
54* d3 foreground color (in the 4 ms bits)
55* d4 background color (in the 4 ms bits)
56* d5 width of the area in bytes
57* d6 scan line counter
58*
59* a0 CG table pointer
60* a1 output area scan line pointer
61* a2 input string character pointer
62*
63* a3 output area character base pointer
64*
65* a6 frame pointer
66* a7 stack pointer
67*
68 .page
69*
70_tsplot4: link a6,#0 * Link stack frames
71 movem.l d3-d6/a3,-(a7) * Save registers we use
72 move.w #PSHIFT,d1 * Set shift constant
73 move.w FG(a6),d3 * Setup foreground color
74 lsl.w d1,d3 * ... in ms 4 bits of d3.W
75 move.w NW(a6),d5 * Get line width in d5.W
76 lsl.w #2,d5 * Multiply width by 4 for offset
77 move.w ROW(a6),d0 * Calculate output address
78 move.w PITCH(a6),d1 * ... PITCH
79 mulu d1,d0 * ... * ROW
80 add.w #VPIX-1,d0 * ... + VPIX-1
81 mulu d5,d0 * ... * NW
82 clr.l d1 * ...
83 move.w COL(a6),d1 * ... +
84 lsl.w #2,d1 * ... COL * 4
85 add.l d1,d0 * ...
86 add.l OBASE(a6),d0 * ... + OBASE
87 movea.l d0,a3 * Leave output address in a3
88 movea.l STR(a6),a2 * Put string address in a2
89*
90cgl0: clr.l d0 * Clear out upper bits of d0
91 move.b (a2)+,d0 * Get next character
92 beq cgl5 * Done if character EQ 0
93*
94 movea.l a3,a1 * Establish output pointer in a1
95 adda.l #HCW,a3 * Update output pointer for next char.
96 lea _cgtable,a0 * Establish CG pointer in a0
97 lsl.w #1,d0 * ... 2 * character
98 adda.w d0,a0 * ... + _cgtable address
99 move.w #VPIX-1,d6 * Set scan line counter in d6
100*
101 .page
102cgl1: move.w (a0),d1 * Get character generator word in d1
103 move.w #(HPIX/2)-1,d2 * Set pixel counter in d2
104 clr.l d4 * Get old output word as background
105 move.w (a1),d4 * ...
106 swap d4 * ...
107*
108cgl2: lsr.w #HSHIFT,d0 * Shift output word right 1 pixel
109 lsr.l #HSHIFT,d4 * Shift background word 1 pixel
110 andi.l #$FFFFF000,d4 * Mask for upper 4 bits of d4.W
111 btst.l #0,d1 * Check CG word ls bit
112 beq cgl3 * Set background color if bit EQ 0
113*
114 or.w d3,d0 * OR foreground color into output word
115 bra cgl4 * Go update CG word
116*
117cgl3: or.w d4,d0 * OR background color into output word
118*
119cgl4: lsr.w #1,d1 * Shift CG word right 1 pixel
120 dbf d2,cgl2 * Loop for first 4 pixels
121*
122 move.w d0,(a1)+ * Store first output word in scan line
123 move.w #(HPIX/2)-1,d2 * Set pixel counter in d2
124 clr.l d4 * Get old output word as background
125 move.w (a1),d4 * ...
126 swap d4 * ...
127*
128cgl2a: lsr.w #HSHIFT,d0 * Shift output word right 1 pixel
129 lsr.l #HSHIFT,d4 * Shift background word 1 pixel
130 andi.l #$FFFFF000,d4 * Mask for upper bits of d4.W
131 btst.l #0,d1 * Check CG word ls bit
132 beq cgl3a * Set background color if bit EQ 0
133*
134 or.w d3,d0 * OR foreground color into output word
135 bra cgl4a * Go update CG word
136*
137cgl3a: or.w d4,d0 * OR background color into output word
138*
139cgl4a: lsr.w #1,d1 * Shift CG word right 1 pixel
140 dbf d2,cgl2a * Loop for last 4 pixels
141*
142 move.w d0,(a1) * Store second output word in scan line
143 suba.w d5,a1 * Update output pointer
144 suba.w #2,a1 * ...
145 adda.l #512,a0 * Update CG pointer for next scan line
146 dbf d6,cgl1 * Loop for all scan lines
147*
148 bra cgl0 * Loop for next character
149*
150cgl5: movem.l (a7)+,d3-d6/a3 * Restore registers
151 unlk a6 * Unlink stack frames
152 rts * Return to caller
153*
154 .end
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