xref: /freebsd/lib/libvgl/simple.c (revision 79483833d06343afe6b87b59b1332e186d1339f8)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 1991-1997 Søren Schmidt
5  * All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer
12  *    in this position and unchanged.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 3. The name of the author may not be used to endorse or promote products
17  *    derived from this software without specific prior written permission
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
20  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
21  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
22  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
23  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
24  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
28  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29  */
30 
31 #include <sys/cdefs.h>
32 __FBSDID("$FreeBSD$");
33 
34 #include <signal.h>
35 #include <sys/fbio.h>
36 #include "vgl.h"
37 
38 static byte VGLSavePaletteRed[256];
39 static byte VGLSavePaletteGreen[256];
40 static byte VGLSavePaletteBlue[256];
41 
42 #define ABS(a)		(((a)<0) ? -(a) : (a))
43 #define SGN(a)		(((a)<0) ? -1 : 1)
44 #define min(x, y)	(((x) < (y)) ? (x) : (y))
45 #define max(x, y)	(((x) > (y)) ? (x) : (y))
46 
47 static void
48 color2mem(u_long color, byte *b, int len)
49 {
50   switch (len) {
51   case 4:
52     b[3] = (color >> 24) & 0xff;
53     /* fallthrough */
54   case 3:
55     b[2] = (color >> 16) & 0xff;
56     /* fallthrough */
57   case 2:
58     b[1] = (color >> 8) & 0xff;
59     /* fallthrough */
60   case 1:
61   default:
62     b[0] = color & 0xff;
63     break;
64   }
65 
66   return;
67 }
68 
69 static u_long
70 mem2color(byte *b, int len)
71 {
72   u_long color = 0;
73 
74   switch (len) {
75   case 4:
76     color |= (b[3] & 0xff) << 24;
77     /* fallthrough */
78   case 3:
79     color |= (b[2] & 0xff) << 16;
80     /* fallthrough */
81   case 2:
82     color |= (b[1] & 0xff) << 8;
83     /* fallthrough */
84   case 1:
85   default:
86     color |= (b[0] & 0xff);
87     break;
88   }
89 
90   return color;
91 }
92 
93 void
94 VGLSetXY(VGLBitmap *object, int x, int y, u_long color)
95 {
96   int offset;
97   byte b[4];
98 
99   VGLCheckSwitch();
100   if (x>=0 && x<object->VXsize && y>=0 && y<object->VYsize) {
101     if (!VGLMouseFreeze(x, y, 1, 1, color)) {
102       switch (object->Type) {
103       case MEMBUF:
104       case VIDBUF8:
105         object->Bitmap[y*object->VXsize+x]=((byte)color);
106         break;
107       case VIDBUF8S:
108 	object->Bitmap[VGLSetSegment(y*object->VXsize+x)]=((byte)color);
109 	break;
110       case VIDBUF16:
111       case VIDBUF24:
112       case VIDBUF32:
113 	color2mem(color, b, object->PixelBytes);
114         bcopy(b, &object->Bitmap[(y*object->VXsize+x) * object->PixelBytes],
115 		object->PixelBytes);
116         break;
117       case VIDBUF16S:
118       case VIDBUF24S:
119       case VIDBUF32S:
120 	color2mem(color, b, object->PixelBytes);
121 	offset = VGLSetSegment((y*object->VXsize+x) * object->PixelBytes);
122 	bcopy(b, &object->Bitmap[offset], object->PixelBytes);
123 	break;
124       case VIDBUF8X:
125         outb(0x3c4, 0x02);
126         outb(0x3c5, 0x01 << (x&0x3));
127 	object->Bitmap[(unsigned)(VGLAdpInfo.va_line_width*y)+(x/4)] = ((byte)color);
128 	break;
129       case VIDBUF4S:
130 	offset = VGLSetSegment(y*VGLAdpInfo.va_line_width + x/8);
131 	goto set_planar;
132       case VIDBUF4:
133 	offset = y*VGLAdpInfo.va_line_width + x/8;
134 set_planar:
135         outb(0x3c4, 0x02); outb(0x3c5, 0x0f);
136         outb(0x3ce, 0x00); outb(0x3cf, (byte)color & 0x0f);	/* set/reset */
137         outb(0x3ce, 0x01); outb(0x3cf, 0x0f);		/* set/reset enable */
138         outb(0x3ce, 0x08); outb(0x3cf, 0x80 >> (x%8));	/* bit mask */
139 	object->Bitmap[offset] |= (byte)color;
140       }
141     }
142     VGLMouseUnFreeze();
143   }
144 }
145 
146 u_long
147 VGLGetXY(VGLBitmap *object, int x, int y)
148 {
149   int offset;
150   byte b[4];
151   int i;
152   u_long color;
153   byte mask;
154 
155   VGLCheckSwitch();
156   if (x<0 || x>=object->VXsize || y<0 || y>=object->VYsize)
157     return 0;
158   switch (object->Type) {
159     case MEMBUF:
160     case VIDBUF8:
161       return object->Bitmap[((y*object->VXsize)+x)];
162     case VIDBUF8S:
163       return object->Bitmap[VGLSetSegment(y*object->VXsize+x)];
164     case VIDBUF16:
165     case VIDBUF24:
166     case VIDBUF32:
167       bcopy(&object->Bitmap[(y*object->VXsize+x) * object->PixelBytes],
168 		b, object->PixelBytes);
169       return (mem2color(b, object->PixelBytes));
170     case VIDBUF16S:
171     case VIDBUF24S:
172     case VIDBUF32S:
173 	offset = VGLSetSegment((y*object->VXsize+x) * object->PixelBytes);
174 	bcopy(&object->Bitmap[offset], b, object->PixelBytes);
175 
176       return (mem2color(b, object->PixelBytes));
177     case VIDBUF8X:
178       outb(0x3ce, 0x04); outb(0x3cf, x & 0x3);
179       return object->Bitmap[(unsigned)(VGLAdpInfo.va_line_width*y)+(x/4)];
180     case VIDBUF4S:
181       offset = VGLSetSegment(y*VGLAdpInfo.va_line_width + x/8);
182       goto get_planar;
183     case VIDBUF4:
184       offset = y*VGLAdpInfo.va_line_width + x/8;
185 get_planar:
186       color = 0;
187       mask = 0x80 >> (x%8);
188       for (i = 0; i < VGLModeInfo.vi_planes; i++) {
189 	outb(0x3ce, 0x04); outb(0x3cf, i);
190 	color |= (((volatile VGLBitmap *)object)->Bitmap[offset] & mask) ?
191 		 (1 << i) : 0;
192       }
193       return color;
194   }
195   return 0;		/* XXX black? */
196 }
197 
198  /*
199   * Symmetric Double Step Line Algorithm by Brian Wyvill from
200   * "Graphics Gems", Academic Press, 1990.
201   */
202 
203 #define SL_SWAP(a,b)           {a^=b; b^=a; a^=b;}
204 #define SL_ABSOLUTE(i,j,k)     ( (i-j)*(k = ( (i-j)<0 ? -1 : 1)))
205 
206 void
207 plot(VGLBitmap * object, int x, int y, int flag, byte color)
208 {
209   /* non-zero flag indicates the pixels need swapping back. */
210   if (flag)
211     VGLSetXY(object, y, x, color);
212   else
213     VGLSetXY(object, x, y, color);
214 }
215 
216 
217 void
218 VGLLine(VGLBitmap *object, int x1, int y1, int x2, int y2, u_long color)
219 {
220   int dx, dy, incr1, incr2, D, x, y, xend, c, pixels_left;
221   int sign_x, sign_y, step, reverse, i;
222 
223   dx = SL_ABSOLUTE(x2, x1, sign_x);
224   dy = SL_ABSOLUTE(y2, y1, sign_y);
225   /* decide increment sign by the slope sign */
226   if (sign_x == sign_y)
227     step = 1;
228   else
229     step = -1;
230 
231   if (dy > dx) {	/* chooses axis of greatest movement (make dx) */
232     SL_SWAP(x1, y1);
233     SL_SWAP(x2, y2);
234     SL_SWAP(dx, dy);
235     reverse = 1;
236   } else
237     reverse = 0;
238   /* note error check for dx==0 should be included here */
239   if (x1 > x2) {      /* start from the smaller coordinate */
240     x = x2;
241     y = y2;
242 /*  x1 = x1;
243     y1 = y1; */
244   } else {
245     x = x1;
246     y = y1;
247     x1 = x2;
248     y1 = y2;
249   }
250 
251 
252   /* Note dx=n implies 0 - n or (dx+1) pixels to be set */
253   /* Go round loop dx/4 times then plot last 0,1,2 or 3 pixels */
254   /* In fact (dx-1)/4 as 2 pixels are already plotted */
255   xend = (dx - 1) / 4;
256   pixels_left = (dx - 1) % 4;  /* number of pixels left over at the
257            * end */
258   plot(object, x, y, reverse, color);
259   if (pixels_left < 0)
260     return;      /* plot only one pixel for zero length
261            * vectors */
262   plot(object, x1, y1, reverse, color);  /* plot first two points */
263   incr2 = 4 * dy - 2 * dx;
264   if (incr2 < 0) {    /* slope less than 1/2 */
265     c = 2 * dy;
266     incr1 = 2 * c;
267     D = incr1 - dx;
268 
269     for (i = 0; i < xend; i++) {  /* plotting loop */
270       ++x;
271       --x1;
272       if (D < 0) {
273         /* pattern 1 forwards */
274         plot(object, x, y, reverse, color);
275         plot(object, ++x, y, reverse, color);
276         /* pattern 1 backwards */
277         plot(object, x1, y1, reverse, color);
278         plot(object, --x1, y1, reverse, color);
279         D += incr1;
280       } else {
281         if (D < c) {
282           /* pattern 2 forwards */
283           plot(object, x, y, reverse, color);
284           plot(object, ++x, y += step, reverse,
285               color);
286           /* pattern 2 backwards */
287           plot(object, x1, y1, reverse, color);
288           plot(object, --x1, y1 -= step, reverse,
289               color);
290         } else {
291           /* pattern 3 forwards */
292           plot(object, x, y += step, reverse, color);
293           plot(object, ++x, y, reverse, color);
294           /* pattern 3 backwards */
295           plot(object, x1, y1 -= step, reverse,
296               color);
297           plot(object, --x1, y1, reverse, color);
298         }
299         D += incr2;
300       }
301     }      /* end for */
302 
303     /* plot last pattern */
304     if (pixels_left) {
305       if (D < 0) {
306         plot(object, ++x, y, reverse, color);  /* pattern 1 */
307         if (pixels_left > 1)
308           plot(object, ++x, y, reverse, color);
309         if (pixels_left > 2)
310           plot(object, --x1, y1, reverse, color);
311       } else {
312         if (D < c) {
313           plot(object, ++x, y, reverse, color);  /* pattern 2  */
314           if (pixels_left > 1)
315             plot(object, ++x, y += step, reverse, color);
316           if (pixels_left > 2)
317             plot(object, --x1, y1, reverse, color);
318         } else {
319           /* pattern 3 */
320           plot(object, ++x, y += step, reverse, color);
321           if (pixels_left > 1)
322             plot(object, ++x, y, reverse, color);
323           if (pixels_left > 2)
324             plot(object, --x1, y1 -= step, reverse, color);
325         }
326       }
327     }      /* end if pixels_left */
328   }
329   /* end slope < 1/2 */
330   else {        /* slope greater than 1/2 */
331     c = 2 * (dy - dx);
332     incr1 = 2 * c;
333     D = incr1 + dx;
334     for (i = 0; i < xend; i++) {
335       ++x;
336       --x1;
337       if (D > 0) {
338         /* pattern 4 forwards */
339         plot(object, x, y += step, reverse, color);
340         plot(object, ++x, y += step, reverse, color);
341         /* pattern 4 backwards */
342         plot(object, x1, y1 -= step, reverse, color);
343         plot(object, --x1, y1 -= step, reverse, color);
344         D += incr1;
345       } else {
346         if (D < c) {
347           /* pattern 2 forwards */
348           plot(object, x, y, reverse, color);
349           plot(object, ++x, y += step, reverse,
350               color);
351 
352           /* pattern 2 backwards */
353           plot(object, x1, y1, reverse, color);
354           plot(object, --x1, y1 -= step, reverse,
355               color);
356         } else {
357           /* pattern 3 forwards */
358           plot(object, x, y += step, reverse, color);
359           plot(object, ++x, y, reverse, color);
360           /* pattern 3 backwards */
361           plot(object, x1, y1 -= step, reverse, color);
362           plot(object, --x1, y1, reverse, color);
363         }
364         D += incr2;
365       }
366     }      /* end for */
367     /* plot last pattern */
368     if (pixels_left) {
369       if (D > 0) {
370         plot(object, ++x, y += step, reverse, color);  /* pattern 4 */
371         if (pixels_left > 1)
372           plot(object, ++x, y += step, reverse,
373               color);
374         if (pixels_left > 2)
375           plot(object, --x1, y1 -= step, reverse,
376               color);
377       } else {
378         if (D < c) {
379           plot(object, ++x, y, reverse, color);  /* pattern 2  */
380           if (pixels_left > 1)
381             plot(object, ++x, y += step, reverse, color);
382           if (pixels_left > 2)
383             plot(object, --x1, y1, reverse, color);
384         } else {
385           /* pattern 3 */
386           plot(object, ++x, y += step, reverse, color);
387           if (pixels_left > 1)
388             plot(object, ++x, y, reverse, color);
389           if (pixels_left > 2) {
390             if (D > c)  /* step 3 */
391               plot(object, --x1, y1 -= step, reverse, color);
392             else  /* step 2 */
393               plot(object, --x1, y1, reverse, color);
394           }
395         }
396       }
397     }
398   }
399 }
400 
401 void
402 VGLBox(VGLBitmap *object, int x1, int y1, int x2, int y2, u_long color)
403 {
404   VGLLine(object, x1, y1, x2, y1, color);
405   VGLLine(object, x2, y1, x2, y2, color);
406   VGLLine(object, x2, y2, x1, y2, color);
407   VGLLine(object, x1, y2, x1, y1, color);
408 }
409 
410 void
411 VGLFilledBox(VGLBitmap *object, int x1, int y1, int x2, int y2, u_long color)
412 {
413   int y;
414 
415   for (y=y1; y<=y2; y++) VGLLine(object, x1, y, x2, y, color);
416 }
417 
418 static inline void
419 set4pixels(VGLBitmap *object, int x, int y, int xc, int yc, u_long color)
420 {
421   if (x!=0) {
422     VGLSetXY(object, xc+x, yc+y, color);
423     VGLSetXY(object, xc-x, yc+y, color);
424     if (y!=0) {
425       VGLSetXY(object, xc+x, yc-y, color);
426       VGLSetXY(object, xc-x, yc-y, color);
427     }
428   }
429   else {
430     VGLSetXY(object, xc, yc+y, color);
431     if (y!=0)
432       VGLSetXY(object, xc, yc-y, color);
433   }
434 }
435 
436 void
437 VGLEllipse(VGLBitmap *object, int xc, int yc, int a, int b, u_long color)
438 {
439   int x = 0, y = b, asq = a*a, asq2 = a*a*2, bsq = b*b;
440   int bsq2 = b*b*2, d = bsq-asq*b+asq/4, dx = 0, dy = asq2*b;
441 
442   while (dx<dy) {
443     set4pixels(object, x, y, xc, yc, color);
444     if (d>0) {
445       y--; dy-=asq2; d-=dy;
446     }
447     x++; dx+=bsq2; d+=bsq+dx;
448   }
449   d+=(3*(asq-bsq)/2-(dx+dy))/2;
450   while (y>=0) {
451     set4pixels(object, x, y, xc, yc, color);
452     if (d<0) {
453       x++; dx+=bsq2; d+=dx;
454     }
455     y--; dy-=asq2; d+=asq-dy;
456   }
457 }
458 
459 static inline void
460 set2lines(VGLBitmap *object, int x, int y, int xc, int yc, u_long color)
461 {
462   if (x!=0) {
463     VGLLine(object, xc+x, yc+y, xc-x, yc+y, color);
464     if (y!=0)
465       VGLLine(object, xc+x, yc-y, xc-x, yc-y, color);
466   }
467   else {
468     VGLLine(object, xc, yc+y, xc, yc-y, color);
469   }
470 }
471 
472 void
473 VGLFilledEllipse(VGLBitmap *object, int xc, int yc, int a, int b, u_long color)
474 {
475   int x = 0, y = b, asq = a*a, asq2 = a*a*2, bsq = b*b;
476   int bsq2 = b*b*2, d = bsq-asq*b+asq/4, dx = 0, dy = asq2*b;
477 
478   while (dx<dy) {
479     set2lines(object, x, y, xc, yc, color);
480     if (d>0) {
481       y--; dy-=asq2; d-=dy;
482     }
483     x++; dx+=bsq2; d+=bsq+dx;
484   }
485   d+=(3*(asq-bsq)/2-(dx+dy))/2;
486   while (y>=0) {
487     set2lines(object, x, y, xc, yc, color);
488     if (d<0) {
489       x++; dx+=bsq2; d+=dx;
490     }
491     y--; dy-=asq2; d+=asq-dy;
492   }
493 }
494 
495 void
496 VGLClear(VGLBitmap *object, u_long color)
497 {
498   int offset;
499   int len;
500   int i, total = 0;
501   byte b[4];
502 
503   VGLCheckSwitch();
504   VGLMouseFreeze(0, 0, object->Xsize, object->Ysize, color); /* XXX */
505   switch (object->Type) {
506   case MEMBUF:
507   case VIDBUF8:
508     memset(object->Bitmap, (byte)color, object->VXsize*object->VYsize);
509     break;
510 
511   case VIDBUF8S:
512     for (offset = 0; offset < object->VXsize*object->VYsize; ) {
513       VGLSetSegment(offset);
514       len = min(object->VXsize*object->VYsize - offset,
515 		VGLAdpInfo.va_window_size);
516       memset(object->Bitmap, (byte)color, len);
517       offset += len;
518     }
519     break;
520   case VIDBUF16:
521   case VIDBUF24:
522   case VIDBUF32:
523     color2mem(color, b, object->PixelBytes);
524     total = object->VXsize*object->VYsize*object->PixelBytes;
525     for (i = 0; i < total; i += object->PixelBytes)
526       bcopy(b, object->Bitmap + i, object->PixelBytes);
527     break;
528 
529   case VIDBUF16S:
530   case VIDBUF24S:
531   case VIDBUF32S:
532     color2mem(color, b, object->PixelBytes);
533     total = object->VXsize*object->VYsize*object->PixelBytes;
534     for (offset = 0; offset < total; ) {
535       VGLSetSegment(offset);
536       len = min(total - offset, VGLAdpInfo.va_window_size);
537       for (i = 0; i < len; i += object->PixelBytes)
538 	bcopy(object->Bitmap + (offset + i) % VGLAdpInfo.va_window_size, b,
539 	      object->PixelBytes);
540       offset += len;
541     }
542     break;
543 
544   case VIDBUF8X:
545     /* XXX works only for Xsize % 4 = 0 */
546     outb(0x3c6, 0xff);
547     outb(0x3c4, 0x02); outb(0x3c5, 0x0f);
548     memset(object->Bitmap, (byte)color, VGLAdpInfo.va_line_width*object->VYsize);
549     break;
550 
551   case VIDBUF4:
552   case VIDBUF4S:
553     /* XXX works only for Xsize % 8 = 0 */
554     outb(0x3c4, 0x02); outb(0x3c5, 0x0f);
555     outb(0x3ce, 0x05); outb(0x3cf, 0x02);		/* mode 2 */
556     outb(0x3ce, 0x01); outb(0x3cf, 0x00);		/* set/reset enable */
557     outb(0x3ce, 0x08); outb(0x3cf, 0xff);		/* bit mask */
558     for (offset = 0; offset < VGLAdpInfo.va_line_width*object->VYsize; ) {
559       VGLSetSegment(offset);
560       len = min(object->VXsize*object->VYsize - offset,
561 		VGLAdpInfo.va_window_size);
562       memset(object->Bitmap, (byte)color, len);
563       offset += len;
564     }
565     outb(0x3ce, 0x05); outb(0x3cf, 0x00);
566     break;
567   }
568   VGLMouseUnFreeze();
569 }
570 
571 void
572 VGLRestorePalette()
573 {
574   int i;
575 
576   outb(0x3C6, 0xFF);
577   inb(0x3DA);
578   outb(0x3C8, 0x00);
579   for (i=0; i<256; i++) {
580     outb(0x3C9, VGLSavePaletteRed[i]);
581     inb(0x84);
582     outb(0x3C9, VGLSavePaletteGreen[i]);
583     inb(0x84);
584     outb(0x3C9, VGLSavePaletteBlue[i]);
585     inb(0x84);
586   }
587   inb(0x3DA);
588   outb(0x3C0, 0x20);
589 }
590 
591 void
592 VGLSavePalette()
593 {
594   int i;
595 
596   outb(0x3C6, 0xFF);
597   inb(0x3DA);
598   outb(0x3C7, 0x00);
599   for (i=0; i<256; i++) {
600     VGLSavePaletteRed[i] = inb(0x3C9);
601     inb(0x84);
602     VGLSavePaletteGreen[i] = inb(0x3C9);
603     inb(0x84);
604     VGLSavePaletteBlue[i] = inb(0x3C9);
605     inb(0x84);
606   }
607   inb(0x3DA);
608   outb(0x3C0, 0x20);
609 }
610 
611 void
612 VGLSetPalette(byte *red, byte *green, byte *blue)
613 {
614   int i;
615 
616   for (i=0; i<256; i++) {
617     VGLSavePaletteRed[i] = red[i];
618     VGLSavePaletteGreen[i] = green[i];
619     VGLSavePaletteBlue[i] = blue[i];
620   }
621   VGLCheckSwitch();
622   outb(0x3C6, 0xFF);
623   inb(0x3DA);
624   outb(0x3C8, 0x00);
625   for (i=0; i<256; i++) {
626     outb(0x3C9, VGLSavePaletteRed[i]);
627     inb(0x84);
628     outb(0x3C9, VGLSavePaletteGreen[i]);
629     inb(0x84);
630     outb(0x3C9, VGLSavePaletteBlue[i]);
631     inb(0x84);
632   }
633   inb(0x3DA);
634   outb(0x3C0, 0x20);
635 }
636 
637 void
638 VGLSetPaletteIndex(byte color, byte red, byte green, byte blue)
639 {
640   VGLSavePaletteRed[color] = red;
641   VGLSavePaletteGreen[color] = green;
642   VGLSavePaletteBlue[color] = blue;
643   VGLCheckSwitch();
644   outb(0x3C6, 0xFF);
645   inb(0x3DA);
646   outb(0x3C8, color);
647   outb(0x3C9, red); outb(0x3C9, green); outb(0x3C9, blue);
648   inb(0x3DA);
649   outb(0x3C0, 0x20);
650 }
651 
652 void
653 VGLSetBorder(byte color)
654 {
655   VGLCheckSwitch();
656   inb(0x3DA);
657   outb(0x3C0,0x11); outb(0x3C0, color);
658   inb(0x3DA);
659   outb(0x3C0, 0x20);
660 }
661 
662 void
663 VGLBlankDisplay(int blank)
664 {
665   byte val;
666 
667   VGLCheckSwitch();
668   outb(0x3C4, 0x01); val = inb(0x3C5); outb(0x3C4, 0x01);
669   outb(0x3C5, ((blank) ? (val |= 0x20) : (val &= 0xDF)));
670 }
671