source: buchla-68k/vlib/vsplot4.s@ b8080f6

Last change on this file since b8080f6 was 4f508e6, checked in by Thomas Lopatic <thomas@…>, 7 years ago

Converted assembly language files.
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File size: 5.0 KB
Line 
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 = 8 | LONG - Output area base address
31NW = 12 | WORD - Character width of output area
32FG = 14 | WORD - Foreground color
33ROW = 16 | WORD - Row
34COL = 18 | WORD - Column
35STR = 20 | LONG - String base address
36PITCH = 24 | WORD - Vertical spacing between rows
37HT = 26 | WORD - Character height
38CGTAB = 28 | LONG - Character generator pionter
39
40| Program constant definitions:
41
42HPIX = 8 | Character width in pixels
43HCW = 4 | Horizontal character width (bytes)
44PSHIFT = 12 | Pixel shift into MS bits
45HSHIFT = 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 #0xFFFFF000,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 #0xFFFFF000,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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