source: buchla-68k/vlib/vsplot4.s@ 109c83b

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

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1* ------------------------------------------------------------------------------
2* vsplot4.s -- output characters to a 4-bit / pixel graphics window
3* with variable vertical pitch, etc.
4* Version 1 -- 1988-10-07 -- D.N. Lynx Crowe
5* (c) Copyright 1988 -- D.N. Lynx Crowe
6* ------------------------------------------------------------------------------
7*
8* vsplot4(obase, nw, fg, row, col, str, pitch, ht, cgtab)
9* uint *obase, nw, fg, row, col, pitch, ht, cgtab[][256];
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 cgtab[][256] as the VSDD formatted character
16* generator table. Assumes 'ht' 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* This function leaves the zero pixels alone and just sets the
21* one pixels to the foreground color, allowing overlapping
22* character cells.
23* ------------------------------------------------------------------------------
24 .text
25*
26 .xdef _vsplot4
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
37HT .equ 26 * WORD - Character height
38CGTAB .equ 28 * LONG - Character generator pionter
39*
40* Program constant definitions:
41*
42HPIX .equ 8 * Character width in pixels
43HCW .equ 4 * Horizontal character width (bytes)
44PSHIFT .equ 12 * Pixel shift into MS bits
45HSHIFT .equ 4 * Pixel right shift
46*
47 .page
48*
49* Register usage:
50*
51* d0 output word and scratch
52* d1 CG word and scratch
53* d2 pixel counter
54*
55* d3 foreground color (in the 4 ms bits)
56* d4 background color (in the 4 ms bits)
57* d5 width of the area in bytes
58* d6 scan line counter
59*
60* a0 CG table pointer
61* a1 output area scan line pointer
62* a2 input string character pointer
63*
64* a3 output area character base pointer
65*
66* a6 frame pointer
67* a7 stack pointer
68*
69 .page
70*
71_vsplot4: link a6,#0 * Link stack frames
72 movem.l d3-d6/a3,-(a7) * Save registers we use
73 move.w #PSHIFT,d1 * Set shift constant
74 move.w FG(a6),d3 * Setup foreground color
75 lsl.w d1,d3 * ... in ms 4 bits of d3.W
76 move.w NW(a6),d5 * Get line width in d5.W
77 lsl.w #2,d5 * Multiply width by 4 for offset
78 move.w ROW(a6),d0 * Calculate output address
79 move.w PITCH(a6),d1 * ... PITCH
80 mulu d1,d0 * ... * ROW
81 add.w HT(a6),d0 * ... + HT-1
82 subq.w #1,d0 * ...
83 mulu d5,d0 * ... * NW
84 clr.l d1 * ...
85 move.w COL(a6),d1 * ... +
86 lsl.w #2,d1 * ... COL * 4
87 add.l d1,d0 * ...
88 add.l OBASE(a6),d0 * ... + OBASE
89 movea.l d0,a3 * Leave output address in a3
90 movea.l STR(a6),a2 * Put string address in a2
91*
92cgl0: clr.l d0 * Clear out upper bits of d0
93 move.b (a2)+,d0 * Get next character
94 beq cgl5 * Done if character EQ 0
95*
96 movea.l a3,a1 * Establish output pointer in a1
97 adda.l #HCW,a3 * Update output pointer for next char.
98 movea.l CGTAB(a6),a0 * Establish CG pointer in a0
99 lsl.w #1,d0 * ... 2 * character
100 adda.w d0,a0 * ... + cgtab address
101 move.w HT(a6),d6 * Set scan line counter in d6
102 subq.w #1,d6 * ...
103*
104 .page
105cgl1: move.w (a0),d1 * Get character generator word in d1
106 move.w #(HPIX/2)-1,d2 * Set pixel counter in d2
107 clr.l d4 * Get old output word as background
108 move.w (a1),d4 * ...
109 swap d4 * ...
110*
111cgl2: lsr.w #HSHIFT,d0 * Shift output word right 1 pixel
112 lsr.l #HSHIFT,d4 * Shift background word 1 pixel
113 andi.l #$FFFFF000,d4 * Mask for upper 4 bits of d4.W
114 btst.l #0,d1 * Check CG word ls bit
115 beq cgl3 * Set background color if bit EQ 0
116*
117 or.w d3,d0 * OR foreground color into output word
118 bra cgl4 * Go update CG word
119*
120cgl3: or.w d4,d0 * OR background color into output word
121*
122cgl4: lsr.w #1,d1 * Shift CG word right 1 pixel
123 dbf d2,cgl2 * Loop for first 4 pixels
124*
125 move.w d0,(a1)+ * Store first output word in scan line
126 move.w #(HPIX/2)-1,d2 * Set pixel counter in d2
127 clr.l d4 * Get old output word as background
128 move.w (a1),d4 * ...
129 swap d4 * ...
130*
131cgl2a: lsr.w #HSHIFT,d0 * Shift output word right 1 pixel
132 lsr.l #HSHIFT,d4 * Shift background word 1 pixel
133 andi.l #$FFFFF000,d4 * Mask for upper bits of d4.W
134 btst.l #0,d1 * Check CG word ls bit
135 beq cgl3a * Set background color if bit EQ 0
136*
137 or.w d3,d0 * OR foreground color into output word
138 bra cgl4a * Go update CG word
139*
140cgl3a: or.w d4,d0 * OR background color into output word
141*
142cgl4a: lsr.w #1,d1 * Shift CG word right 1 pixel
143 dbf d2,cgl2a * Loop for last 4 pixels
144*
145 move.w d0,(a1) * Store second output word in scan line
146 suba.w d5,a1 * Update output pointer
147 suba.w #2,a1 * ...
148 adda.l #512,a0 * Update CG pointer for next scan line
149 dbf d6,cgl1 * Loop for all scan lines
150*
151 bra cgl0 * Loop for next character
152*
153cgl5: movem.l (a7)+,d3-d6/a3 * Restore registers
154 unlk a6 * Unlink stack frames
155 rts * Return to caller
156*
157 .end
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