wrlib/context.c

   1 /* context.c - X context management
   2  *
   3  *  Raster graphics library
   4  *
   5  *  Copyright (c) 1997, 1998, 1999 Alfredo K. Kojima
   6  *
   7  *  This library is free software; you can redistribute it and/or
   8  *  modify it under the terms of the GNU Library General Public
   9  *  License as published by the Free Software Foundation; either
  10  *  version 2 of the License, or (at your option) any later version.
  11  *
  12  *  This library is distributed in the hope that it will be useful,
  13  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  *  Library General Public License for more details.
  16  *
  17  *  You should have received a copy of the GNU Library General Public
  18  *  License along with this library; if not, write to the Free
  19  *  Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20  */
  21
  22 #include <config.h>
  23
  24 #include <X11/Xlib.h>
  25 #include <X11/Xutil.h>
  26 #include <X11/Xatom.h>
  27
  28 #include <stdio.h>
  29 #include <stdlib.h>
  30 #include <string.h>
  31 #include <assert.h>
  32
  33 #include <math.h>
  34
  35 #include "StdCmap.h"
  36
  37 #include "wraster.h"
  38
  39
  40 extern void _wraster_change_filter(int type);
  41
  42
  43 static Bool bestContext(Display *dpy, int screen_number, RContext *context);
  44
  45 static RContextAttributes DEFAULT_CONTEXT_ATTRIBS = {
  46     RC_UseSharedMemory|RC_RenderMode|RC_ColorsPerChannel, /* flags */
  47         RDitheredRendering,                    /* render_mode */
  48         4,                             /* colors_per_channel */
  49         0,
  50         0,
  51         0,
  52         0,
  53         True,                              /* use_shared_memory */
  54         RMitchellFilter,
  55         RUseStdColormap
  56 };
  57
  58
  59
  60 /*
  61  *
  62  * Colormap allocation for PseudoColor visuals:
  63  *
  64  *
  65  * switch standardColormap:
  66  *      none:
  67  *              allocate colors according to colors_per_channel
  68  *
  69  *      best/default:
  70  *              if there's a std colormap defined then use it
  71  *
  72  *              else
  73  *                      create a std colormap and set it
  74  */
  75
  76
  77
  78
  79 /*
  80  *----------------------------------------------------------------------
  81  * allocateStandardPseudoColor
  82  *      Creates the internal colormap for PseudoColor, setting the
  83  * color values according to the supplied standard colormap.
  84  *
  85  * Returns: -
  86  *
  87  * Side effects: -
  88  *
  89  * Notes: -
  90  *----------------------------------------------------------------------
  91  */
  92 static Bool
  93 allocateStandardPseudoColor(RContext *ctx, XStandardColormap *stdcmap)
  94 {
  95     int i;
  96
  97     ctx->ncolors = stdcmap->red_max * stdcmap->red_mult
  98         + stdcmap->green_max * stdcmap->green_mult
  99         + stdcmap->blue_max * stdcmap->blue_mult + 1;
 100
 101     if (ctx->ncolors <= 1) {
 102         RErrorCode = RERR_INTERNAL;
 103         puts("wraster: bad standard colormap");
 104
 105         return False;
 106     }
 107
 108     ctx->colors = malloc(sizeof(XColor)*ctx->ncolors);
 109     if (!ctx->colors) {
 110         RErrorCode = RERR_NOMEMORY;
 111
 112         return False;
 113     }
 114
 115     ctx->pixels = malloc(sizeof(unsigned long)*ctx->ncolors);
 116     if (!ctx->pixels) {
 117
 118         free(ctx->colors);
 119         ctx->colors = NULL;
 120
 121         RErrorCode = RERR_NOMEMORY;
 122
 123         return False;
 124     }
 125
 126
 127 #define calc(max,mult) (((i / stdcmap->mult) % \
 128                          (stdcmap->max + 1)) * 65535) / stdcmap->max
 129
 130     for (i = 0; i < ctx->ncolors; i++) {
 131         ctx->colors[i].pixel = i + stdcmap->base_pixel;
 132         ctx->colors[i].red = calc(red_max, red_mult);
 133         ctx->colors[i].green = calc(green_max, green_mult);
 134         ctx->colors[i].blue = calc(blue_max, blue_mult);
 135
 136         ctx->pixels[i] = ctx->colors[i].pixel;
 137     }
 138
 139 #undef calc
 140
 141     return True;
 142 }
 143
 144
 145 static Bool
 146 setupStandardColormap(RContext *ctx, Atom property)
 147 {
 148     if (!XmuLookupStandardColormap(ctx->dpy, ctx->screen_number,
 149                                    ctx->visual->visualid,
 150                                    ctx->depth, property,
 151                                    True, True)) {
 152         RErrorCode = RERR_STDCMAPFAIL;
 153
 154         return False;
 155     }
 156     return True;
 157 }
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167 static Bool
 168 allocatePseudoColor(RContext *ctx)
 169 {
 170     XColor *colors;
 171     XColor avcolors[256];
 172     int avncolors;
 173     int i, ncolors, r, g, b;
 174     int retries;
 175     int cpc = ctx->attribs->colors_per_channel;
 176
 177     ncolors = cpc * cpc * cpc;
 178
 179     if (ncolors > (1<<ctx->depth)) {
 180         /* reduce colormap size */
 181         cpc = ctx->attribs->colors_per_channel = 1<<((int)ctx->depth/3);
 182         ncolors = cpc * cpc * cpc;
 183     }
 184
 185     assert(cpc >= 2 && ncolors <= (1<<ctx->depth));
 186
 187     colors = malloc(sizeof(XColor)*ncolors);
 188     if (!colors) {
 189         RErrorCode = RERR_NOMEMORY;
 190         return False;
 191     }
 192
 193     ctx->pixels = malloc(sizeof(unsigned long)*ncolors);
 194     if (!ctx->pixels) {
 195         free(colors);
 196         RErrorCode = RERR_NOMEMORY;
 197         return False;
 198     }
 199
 200     i=0;
 201
 202     if ((ctx->attribs->flags & RC_GammaCorrection) && ctx->attribs->rgamma > 0
 203         && ctx->attribs->ggamma > 0 && ctx->attribs->bgamma > 0) {
 204         double rg, gg, bg;
 205         double tmp;
 206
 207         /* do gamma correction */
 208         rg = 1.0/ctx->attribs->rgamma;
 209         gg = 1.0/ctx->attribs->ggamma;
 210         bg = 1.0/ctx->attribs->bgamma;
 211         for (r=0; r<cpc; r++) {
 212             for (g=0; g<cpc; g++) {
 213                 for (b=0; b<cpc; b++) {
 214                     colors[i].red=(r*0xffff) / (cpc-1);
 215                     colors[i].green=(g*0xffff) / (cpc-1);
 216                     colors[i].blue=(b*0xffff) / (cpc-1);
 217                     colors[i].flags = DoRed|DoGreen|DoBlue;
 218
 219                     tmp = (double)colors[i].red / 65536.0;
 220                     colors[i].red = (unsigned short)(65536.0*pow(tmp, rg));
 221
 222                     tmp = (double)colors[i].green / 65536.0;
 223                     colors[i].green = (unsigned short)(65536.0*pow(tmp, gg));
 224
 225                     tmp = (double)colors[i].blue / 65536.0;
 226                     colors[i].blue = (unsigned short)(65536.0*pow(tmp, bg));
 227
 228                     i++;
 229                 }
 230             }
 231         }
 232
 233     } else {
 234         for (r=0; r<cpc; r++) {
 235             for (g=0; g<cpc; g++) {
 236                 for (b=0; b<cpc; b++) {
 237                     colors[i].red=(r*0xffff) / (cpc-1);
 238                     colors[i].green=(g*0xffff) / (cpc-1);
 239                     colors[i].blue=(b*0xffff) / (cpc-1);
 240                     colors[i].flags = DoRed|DoGreen|DoBlue;
 241                     i++;
 242                 }
 243             }
 244         }
 245     }
 246     /* try to allocate the colors */
 247     for (i=0; i<ncolors; i++) {
 248         if (!XAllocColor(ctx->dpy, ctx->cmap, &(colors[i]))) {
 249             colors[i].flags = 0; /* failed */
 250         } else {
 251             colors[i].flags = DoRed|DoGreen|DoBlue;
 252         }
 253     }
 254     /* try to allocate close values for the colors that couldn't
 255      * be allocated before */
 256     avncolors = (1<<ctx->depth>256 ? 256 : 1<<ctx->depth);
 257     for (i=0; i<avncolors; i++) avcolors[i].pixel = i;
 258
 259     XQueryColors(ctx->dpy, ctx->cmap, avcolors, avncolors);
 260
 261     for (i=0; i<ncolors; i++) {
 262         if (colors[i].flags==0) {
 263             int j;
 264             unsigned long cdiff=0xffffffff, diff;
 265             unsigned long closest=0;
 266
 267             retries = 2;
 268
 269             while (retries--) {
 270                 /* find closest color */
 271                 for (j=0; j<avncolors; j++) {
 272                     r = (colors[i].red - avcolors[i].red)>>8;
 273                     g = (colors[i].green - avcolors[i].green)>>8;
 274                     b = (colors[i].blue - avcolors[i].blue)>>8;
 275                     diff = r*r + g*g + b*b;
 276                     if (diff<cdiff) {
 277                         cdiff = diff;
 278                         closest = j;
 279                     }
 280                 }
 281                 /* allocate closest color found */
 282                 colors[i].red = avcolors[closest].red;
 283                 colors[i].green = avcolors[closest].green;
 284                 colors[i].blue = avcolors[closest].blue;
 285                 if (XAllocColor(ctx->dpy, ctx->cmap, &colors[i])) {
 286                     colors[i].flags = DoRed|DoGreen|DoBlue;
 287                     break; /* succeeded, don't need to retry */
 288                 }
 289 #ifdef DEBUG
 290                 printf("close color allocation failed. Retrying...\n");
 291 #endif
 292             }
 293         }
 294     }
 295
 296     ctx->colors = colors;
 297     ctx->ncolors = ncolors;
 298
 299     /* fill the pixels shortcut array */
 300     for (i = 0; i < ncolors; i++) {
 301         ctx->pixels[i] = ctx->colors[i].pixel;
 302     }
 303
 304     return True;
 305 }
 306
 307
 308 static XColor*
 309 allocateGrayScale(RContext *ctx)
 310 {
 311     XColor *colors;
 312     XColor avcolors[256];
 313     int avncolors;
 314     int i, ncolors, r, g, b;
 315     int retries;
 316     int cpc = ctx->attribs->colors_per_channel;
 317
 318     ncolors = cpc * cpc * cpc;
 319
 320     if (ctx->vclass == StaticGray) {
 321       /* we might as well use all grays */
 322       ncolors = 1<<ctx->depth;
 323     } else {
 324         if ( ncolors > (1<<ctx->depth) ) {
 325             /* reduce colormap size */
 326             cpc = ctx->attribs->colors_per_channel = 1<<((int)ctx->depth/3);
 327             ncolors = cpc * cpc * cpc;
 328         }
 329
 330         assert(cpc >= 2 && ncolors <= (1<<ctx->depth));
 331     }
 332
 333     if (ncolors>=256 && ctx->vclass==StaticGray) {
 334         /* don't need dithering for 256 levels of gray in StaticGray visual */
 335         ctx->attribs->render_mode = RBestMatchRendering;
 336     }
 337
 338     colors = malloc(sizeof(XColor)*ncolors);
 339     if (!colors) {
 340         RErrorCode = RERR_NOMEMORY;
 341         return False;
 342     }
 343     for (i=0; i<ncolors; i++) {
 344         colors[i].red=(i*0xffff) / (ncolors-1);
 345         colors[i].green=(i*0xffff) / (ncolors-1);
 346         colors[i].blue=(i*0xffff) / (ncolors-1);
 347         colors[i].flags = DoRed|DoGreen|DoBlue;
 348     }
 349     /* try to allocate the colors */
 350     for (i=0; i<ncolors; i++) {
 351 #ifdef DEBUG
 352         printf("trying:%x,%x,%x\n",colors[i].red,colors[i].green,colors[i].blue);
 353 #endif
 354         if (!XAllocColor(ctx->dpy, ctx->cmap, &(colors[i]))) {
 355             colors[i].flags = 0; /* failed */
 356 #ifdef DEBUG
 357             printf("failed:%x,%x,%x\n",colors[i].red,colors[i].green,colors[i].blue);
 358 #endif
 359         } else {
 360             colors[i].flags = DoRed|DoGreen|DoBlue;
 361 #ifdef DEBUG
 362             printf("success:%x,%x,%x\n",colors[i].red,colors[i].green,colors[i].blue);
 363 #endif
 364         }
 365     }
 366     /* try to allocate close values for the colors that couldn't
 367      * be allocated before */
 368     avncolors = (1<<ctx->depth>256 ? 256 : 1<<ctx->depth);
 369     for (i=0; i<avncolors; i++) avcolors[i].pixel = i;
 370
 371     XQueryColors(ctx->dpy, ctx->cmap, avcolors, avncolors);
 372
 373     for (i=0; i<ncolors; i++) {
 374         if (colors[i].flags==0) {
 375             int j;
 376             unsigned long cdiff=0xffffffff, diff;
 377             unsigned long closest=0;
 378
 379             retries = 2;
 380
 381             while (retries--) {
 382                 /* find closest color */
 383                 for (j=0; j<avncolors; j++) {
 384                     r = (colors[i].red - avcolors[i].red)>>8;
 385                     g = (colors[i].green - avcolors[i].green)>>8;
 386                     b = (colors[i].blue - avcolors[i].blue)>>8;
 387                     diff = r*r + g*g + b*b;
 388                     if (diff<cdiff) {
 389                         cdiff = diff;
 390                         closest = j;
 391                     }
 392                 }
 393                 /* allocate closest color found */
 394 #ifdef DEBUG
 395                 printf("best match:%x,%x,%x => %x,%x,%x\n",colors[i].red,colors[i].green,colors[i].blue,avcolors[closest].red,avcolors[closest].green,avcolors[closest].blue);
 396 #endif
 397                 colors[i].red = avcolors[closest].red;
 398                 colors[i].green = avcolors[closest].green;
 399                 colors[i].blue = avcolors[closest].blue;
 400                 if (XAllocColor(ctx->dpy, ctx->cmap, &colors[i])) {
 401                     colors[i].flags = DoRed|DoGreen|DoBlue;
 402                     break; /* succeeded, don't need to retry */
 403                 }
 404 #ifdef DEBUG
 405                 printf("close color allocation failed. Retrying...\n");
 406 #endif
 407             }
 408         }
 409     }
 410     return colors;
 411 }
 412
 413
 414 static Bool
 415 setupPseudoColorColormap(RContext *context)
 416 {
 417     Atom property = 0;
 418
 419     if (context->attribs->standard_colormap_mode == RCreateStdColormap) {
 420         property = XInternAtom(context->dpy, "RGB_DEFAULT_MAP", False);
 421
 422         if (!setupStandardColormap(context, property)) {
 423             return False;
 424         }
 425     }
 426
 427     if (context->attribs->standard_colormap_mode != RIgnoreStdColormap) {
 428         XStandardColormap *maps;
 429         int count, i;
 430
 431         if (!property) {
 432             property = XInternAtom(context->dpy, "RGB_BEST_MAP", False);
 433             if (!XGetRGBColormaps(context->dpy,
 434                                   DefaultRootWindow(context->dpy),
 435                                   &maps, &count, property)) {
 436                 maps = NULL;
 437             }
 438
 439             if (!maps) {
 440                 property = XInternAtom(context->dpy, "RGB_DEFAULT_MAP", False);
 441                 if (!XGetRGBColormaps(context->dpy,
 442                                       DefaultRootWindow(context->dpy),
 443                                       &maps, &count, property)) {
 444                     maps = NULL;
 445                 }
 446             }
 447         } else {
 448             if (!XGetRGBColormaps(context->dpy,
 449                                   DefaultRootWindow(context->dpy),
 450                                   &maps, &count, property)) {
 451                 maps = NULL;
 452             }
 453         }
 454
 455         if (maps) {
 456             int theMap = -1;
 457
 458             for (i = 0; i < count; i++) {
 459                 if (maps[i].visualid == context->visual->visualid) {
 460                     theMap = i;
 461                     break;
 462                 }
 463             }
 464
 465             if (theMap < 0) {
 466                 puts("wrlib: no std cmap found");
 467             }
 468
 469             if (theMap >= 0
 470                 && allocateStandardPseudoColor(context, &maps[theMap])) {
 471
 472                 context->std_rgb_map = XAllocStandardColormap();
 473
 474                 *context->std_rgb_map = maps[theMap];
 475
 476                 context->cmap = context->std_rgb_map->colormap;
 477
 478                 XFree(maps);
 479
 480                 return True;
 481             }
 482
 483             XFree(maps);
 484         }
 485     }
 486
 487     context->attribs->standard_colormap_mode = RIgnoreStdColormap;
 488
 489     /* RIgnoreStdColormap and fallback */
 490     return allocatePseudoColor(context);
 491 }
 492
 493
 494
 495
 496 static char*
 497 mygetenv(char *var, int scr)
 498 {
 499     char *p;
 500     char varname[64];
 501
 502     sprintf(varname, "%s%i", var, scr);
 503     p = getenv(varname);
 504     if (!p) {
 505         p = getenv(var);
 506     }
 507     return p;
 508 }
 509
 510
 511 static void
 512 gatherconfig(RContext *context, int screen_n)
 513 {
 514     char *ptr;
 515
 516     ptr = mygetenv("WRASTER_GAMMA", screen_n);
 517     if (ptr) {
 518         float g1,g2,g3;
 519         if (sscanf(ptr, "%f/%f/%f", &g1, &g2, &g3)!=3
 520             || g1<=0.0 || g2<=0.0 || g3<=0.0) {
 521             printf("wrlib: invalid value(s) for gamma correction \"%s\"\n",
 522                    ptr);
 523         } else {
 524             context->attribs->flags |= RC_GammaCorrection;
 525             context->attribs->rgamma = g1;
 526             context->attribs->ggamma = g2;
 527             context->attribs->bgamma = g3;
 528         }
 529     }
 530     ptr = mygetenv("WRASTER_COLOR_RESOLUTION", screen_n);
 531     if (ptr) {
 532         int i;
 533         if (sscanf(ptr, "%d", &i)!=1 || i<2 || i>6) {
 534             printf("wrlib: invalid value for color resolution \"%s\"\n",ptr);
 535         } else {
 536             context->attribs->flags |= RC_ColorsPerChannel;
 537             context->attribs->colors_per_channel = i;
 538         }
 539     }
 540
 541     ptr = mygetenv("WRASTER_OPTIMIZE_FOR_SPEED", screen_n);
 542     if (ptr) {
 543         context->flags.optimize_for_speed = 1;
 544     } else {
 545         context->flags.optimize_for_speed = 0;
 546     }
 547
 548 }
 549
 550
 551 static void
 552 getColormap(RContext *context, int screen_number)
 553 {
 554     Colormap cmap = None;
 555     XStandardColormap *cmaps;
 556     int ncmaps, i;
 557
 558     if (XGetRGBColormaps(context->dpy,
 559                          RootWindow(context->dpy, screen_number),
 560                          &cmaps, &ncmaps, XA_RGB_DEFAULT_MAP)) {
 561         for (i=0; i<ncmaps; ++i) {
 562             if (cmaps[i].visualid == context->visual->visualid) {
 563                 puts("ACHOU");
 564                 cmap = cmaps[i].colormap;
 565                 break;
 566             }
 567         }
 568         XFree(cmaps);
 569     }
 570     if (cmap == None) {
 571         XColor color;
 572
 573         cmap = XCreateColormap(context->dpy,
 574                                RootWindow(context->dpy, screen_number),
 575                                context->visual, AllocNone);
 576
 577         color.red = color.green = color.blue = 0;
 578         XAllocColor(context->dpy, cmap, &color);
 579         context->black = color.pixel;
 580
 581         color.red = color.green = color.blue = 0xffff;
 582         XAllocColor(context->dpy, cmap, &color);
 583         context->white = color.pixel;
 584
 585     }
 586     context->cmap = cmap;
 587 }
 588
 589
 590 static int
 591 count_offset(unsigned long mask)
 592 {
 593     int i;
 594
 595     i=0;
 596     while ((mask & 1)==0) {
 597         i++;
 598         mask = mask >> 1;
 599     }
 600     return i;
 601 }
 602
 603
 604 RContext*
 605 RCreateContext(Display *dpy, int screen_number, RContextAttributes *attribs)
 606 {
 607     RContext *context;
 608     XGCValues gcv;
 609
 610
 611     context = malloc(sizeof(RContext));
 612     if (!context) {
 613         RErrorCode = RERR_NOMEMORY;
 614         return NULL;
 615     }
 616     memset(context, 0, sizeof(RContext));
 617
 618     context->dpy = dpy;
 619
 620     context->screen_number = screen_number;
 621
 622     context->attribs = malloc(sizeof(RContextAttributes));
 623     if (!context->attribs) {
 624         free(context);
 625         RErrorCode = RERR_NOMEMORY;
 626         return NULL;
 627     }
 628     if (!attribs)
 629         *context->attribs = DEFAULT_CONTEXT_ATTRIBS;
 630     else
 631         *context->attribs = *attribs;
 632
 633     if (!(context->attribs->flags & RC_StandardColormap)) {
 634         context->attribs->standard_colormap_mode = RUseStdColormap;
 635     }
 636
 637     if (!(context->attribs->flags & RC_ScalingFilter)) {
 638         context->attribs->flags |= RC_ScalingFilter;
 639         context->attribs->scaling_filter = RMitchellFilter;
 640     }
 641
 642     /* get configuration from environment variables */
 643     gatherconfig(context, screen_number);
 644 #ifndef BENCH
 645     _wraster_change_filter(context->attribs->scaling_filter);
 646 #endif
 647     if ((context->attribs->flags & RC_VisualID)) {
 648         XVisualInfo *vinfo, templ;
 649         int nret;
 650
 651         templ.screen = screen_number;
 652         templ.visualid = context->attribs->visualid;
 653         vinfo = XGetVisualInfo(context->dpy, VisualIDMask|VisualScreenMask,
 654                                &templ, &nret);
 655         if (!vinfo || nret==0) {
 656             free(context);
 657             RErrorCode = RERR_BADVISUALID;
 658             return NULL;
 659         }
 660
 661         if (vinfo[0].visual == DefaultVisual(dpy, screen_number)) {
 662             context->attribs->flags |= RC_DefaultVisual;
 663         } else {
 664             XSetWindowAttributes attr;
 665             unsigned long mask;
 666
 667             context->visual = vinfo[0].visual;
 668             context->depth = vinfo[0].depth;
 669             context->vclass = vinfo[0].class;
 670             getColormap(context, screen_number);
 671             attr.colormap = context->cmap;
 672             attr.override_redirect = True;
 673             attr.border_pixel = 0;
 674             attr.background_pixel = 0;
 675             mask = CWBorderPixel|CWColormap|CWOverrideRedirect|CWBackPixel;
 676             context->drawable =
 677                 XCreateWindow(dpy, RootWindow(dpy, screen_number), 1, 1,
 678                               1, 1, 0, context->depth, CopyFromParent,
 679                               context->visual, mask, &attr);
 680             /*          XSetWindowColormap(dpy, context->drawable, attr.colormap);*/
 681         }
 682         XFree(vinfo);
 683     }
 684
 685     /* use default */
 686     if (!context->visual) {
 687         if ((context->attribs->flags & RC_DefaultVisual)
 688             || !bestContext(dpy, screen_number, context)) {
 689             context->visual = DefaultVisual(dpy, screen_number);
 690             context->depth = DefaultDepth(dpy, screen_number);
 691             context->cmap = DefaultColormap(dpy, screen_number);
 692             context->drawable = RootWindow(dpy, screen_number);
 693             context->black = BlackPixel(dpy, screen_number);
 694             context->white = WhitePixel(dpy, screen_number);
 695             context->vclass = context->visual->class;
 696         }
 697     }
 698
 699     gcv.function = GXcopy;
 700     gcv.graphics_exposures = False;
 701     context->copy_gc = XCreateGC(dpy, context->drawable, GCFunction
 702                                  |GCGraphicsExposures, &gcv);
 703
 704     if (context->vclass == PseudoColor || context->vclass == StaticColor) {
 705
 706         if (!setupPseudoColorColormap(context)) {
 707             return NULL;
 708         }
 709
 710     } else if (context->vclass == GrayScale || context->vclass == StaticGray) {
 711         context->colors = allocateGrayScale(context);
 712         if (!context->colors) {
 713             return NULL;
 714         }
 715     } else if (context->vclass == TrueColor) {
 716         /* calc offsets to create a TrueColor pixel */
 717         context->red_offset = count_offset(context->visual->red_mask);
 718         context->green_offset = count_offset(context->visual->green_mask);
 719         context->blue_offset = count_offset(context->visual->blue_mask);
 720         /* disable dithering on 24 bits visuals */
 721         if (context->depth >= 24)
 722             context->attribs->render_mode = RBestMatchRendering;
 723     }
 724
 725     /* check avaiability of MIT-SHM */
 726 #ifdef XSHM
 727     if (!(context->attribs->flags & RC_UseSharedMemory)) {
 728         context->attribs->flags |= RC_UseSharedMemory;
 729         context->attribs->use_shared_memory = True;
 730     }
 731
 732     if (context->attribs->use_shared_memory) {
 733         int major, minor;
 734         Bool sharedPixmaps;
 735
 736         context->flags.use_shared_pixmap = 0;
 737
 738         if (!XShmQueryVersion(context->dpy, &major, &minor, &sharedPixmaps)) {
 739             context->attribs->use_shared_memory = False;
 740         } else {
 741             if (XShmPixmapFormat(context->dpy)==ZPixmap)
 742                 context->flags.use_shared_pixmap = sharedPixmaps;
 743         }
 744     }
 745 #endif
 746
 747     return context;
 748 }
 749
 750
 751 static Bool
 752 bestContext(Display *dpy, int screen_number, RContext *context)
 753 {
 754     XVisualInfo *vinfo=NULL, rvinfo;
 755     int best = -1, numvis, i;
 756     long flags;
 757     XSetWindowAttributes attr;
 758
 759     rvinfo.class  = TrueColor;
 760     rvinfo.screen = screen_number;
 761     flags = VisualClassMask | VisualScreenMask;
 762
 763     vinfo = XGetVisualInfo(dpy, flags, &rvinfo, &numvis);
 764     if (vinfo) {     /* look for a TrueColor, 24-bit or more (pref 24) */
 765         for (i=numvis-1, best = -1; i>=0; i--) {
 766             if (vinfo[i].depth == 24) best = i;
 767             else if (vinfo[i].depth>24 && best<0) best = i;
 768         }
 769     }
 770
 771 #if 0
 772     if (best == -1) {   /* look for a DirectColor, 24-bit or more (pref 24) */
 773         rvinfo.class = DirectColor;
 774         if (vinfo) XFree((char *) vinfo);
 775         vinfo = XGetVisualInfo(dpy, flags, &rvinfo, &numvis);
 776         if (vinfo) {
 777             for (i=0, best = -1; i<numvis; i++) {
 778                 if (vinfo[i].depth == 24) best = i;
 779                 else if (vinfo[i].depth>24 && best<0) best = i;
 780             }
 781         }
 782     }
 783 #endif
 784     if (best > -1) {
 785         context->visual = vinfo[best].visual;
 786         context->depth = vinfo[best].depth;
 787         context->vclass = vinfo[best].class;
 788         getColormap(context, screen_number);
 789         attr.colormap = context->cmap;
 790         attr.override_redirect = True;
 791         attr.border_pixel = 0;
 792         context->drawable =
 793             XCreateWindow(dpy, RootWindow(dpy, screen_number),
 794                           1, 1, 1, 1, 0, context->depth,
 795                           CopyFromParent, context->visual,
 796                           CWBorderPixel|CWColormap|CWOverrideRedirect, &attr);
 797 /*      XSetWindowColormap(dpy, context->drawable, context->cmap);*/
 798     }
 799     if (vinfo) XFree((char *) vinfo);
 800
 801     if (best < 0)
 802         return False;
 803     else
 804         return True;
 805 }