wrlib/context.c

   1 /* context.c - X context management
   2  *
   3  * Raster graphics library
   4  *
   5  * Copyright (c) 1997-2003 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., 51 Franklin St, Fifth Floor, Boston,
  20  *  MA 02110-1301, USA.
  21  */
  22
  23 #include <config.h>
  24
  25 #include <X11/Xlib.h>
  26 #include <X11/Xutil.h>
  27 #include <X11/Xatom.h>
  28 #include <X11/Xmu/StdCmap.h>
  29
  30 #include <stdio.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33 #include <assert.h>
  34
  35 #include <math.h>
  36
  37 #include "wraster.h"
  38
  39 extern void _wraster_change_filter(int type);
  40
  41 static Bool bestContext(Display * dpy, int screen_number, RContext * context);
  42
  43 static RContextAttributes DEFAULT_CONTEXT_ATTRIBS = {
  44         RC_UseSharedMemory | RC_RenderMode | RC_ColorsPerChannel,       /* flags */
  45         RDitheredRendering,     /* render_mode */
  46         4,                      /* colors_per_channel */
  47         0,
  48         0,
  49         0,
  50         0,
  51         True,                   /* use_shared_memory */
  52         RMitchellFilter,
  53         RUseStdColormap
  54 };
  55
  56 /*
  57  *
  58  * Colormap allocation for PseudoColor visuals:
  59  *
  60  *
  61  * switch standardColormap:
  62  *      none:
  63  *              allocate colors according to colors_per_channel
  64  *
  65  *      best/default:
  66  *              if there's a std colormap defined then use it
  67  *
  68  *              else
  69  *                      create a std colormap and set it
  70  */
  71
  72 /*
  73  *----------------------------------------------------------------------
  74  * allocateStandardPseudoColor
  75  *      Creates the internal colormap for PseudoColor, setting the
  76  * color values according to the supplied standard colormap.
  77  *
  78  * Returns: -
  79  *
  80  * Side effects: -
  81  *
  82  * Notes: -
  83  *----------------------------------------------------------------------
  84  */
  85 static Bool allocateStandardPseudoColor(RContext * ctx, XStandardColormap * stdcmap)
  86 {
  87         int i;
  88
  89         ctx->ncolors = stdcmap->red_max * stdcmap->red_mult
  90             + stdcmap->green_max * stdcmap->green_mult + stdcmap->blue_max * stdcmap->blue_mult + 1;
  91
  92         if (ctx->ncolors <= 1) {
  93                 RErrorCode = RERR_INTERNAL;
  94                 puts("wraster: bad standard colormap");
  95
  96                 return False;
  97         }
  98
  99         ctx->colors = malloc(sizeof(XColor) * ctx->ncolors);
 100         if (!ctx->colors) {
 101                 RErrorCode = RERR_NOMEMORY;
 102
 103                 return False;
 104         }
 105
 106         ctx->pixels = malloc(sizeof(unsigned long) * ctx->ncolors);
 107         if (!ctx->pixels) {
 108
 109                 free(ctx->colors);
 110                 ctx->colors = NULL;
 111
 112                 RErrorCode = RERR_NOMEMORY;
 113
 114                 return False;
 115         }
 116
 117 #define calc(max,mult) (((i / stdcmap->mult) % \
 118     (stdcmap->max + 1)) * 65535) / stdcmap->max
 119
 120         for (i = 0; i < ctx->ncolors; i++) {
 121                 ctx->colors[i].pixel = i + stdcmap->base_pixel;
 122                 ctx->colors[i].red = calc(red_max, red_mult);
 123                 ctx->colors[i].green = calc(green_max, green_mult);
 124                 ctx->colors[i].blue = calc(blue_max, blue_mult);
 125
 126                 ctx->pixels[i] = ctx->colors[i].pixel;
 127         }
 128
 129 #undef calc
 130
 131         return True;
 132 }
 133
 134 static Bool setupStandardColormap(RContext * ctx, Atom property)
 135 {
 136         if (!XmuLookupStandardColormap(ctx->dpy, ctx->screen_number,
 137                                        ctx->visual->visualid, ctx->depth, property, True, True)) {
 138                 RErrorCode = RERR_STDCMAPFAIL;
 139
 140                 return False;
 141         }
 142         return True;
 143 }
 144
 145 static Bool allocatePseudoColor(RContext * ctx)
 146 {
 147         XColor *colors;
 148         XColor avcolors[256];
 149         int avncolors;
 150         int i, ncolors, r, g, b;
 151         int retries;
 152         int cpc = ctx->attribs->colors_per_channel;
 153
 154         ncolors = cpc * cpc * cpc;
 155
 156         if (ncolors > (1 << ctx->depth)) {
 157                 /* reduce colormap size */
 158                 cpc = ctx->attribs->colors_per_channel = 1 << ((int)ctx->depth / 3);
 159                 ncolors = cpc * cpc * cpc;
 160         }
 161
 162         assert(cpc >= 2 && ncolors <= (1 << ctx->depth));
 163
 164         colors = malloc(sizeof(XColor) * ncolors);
 165         if (!colors) {
 166                 RErrorCode = RERR_NOMEMORY;
 167                 return False;
 168         }
 169
 170         ctx->pixels = malloc(sizeof(unsigned long) * ncolors);
 171         if (!ctx->pixels) {
 172                 free(colors);
 173                 RErrorCode = RERR_NOMEMORY;
 174                 return False;
 175         }
 176
 177         i = 0;
 178
 179         if ((ctx->attribs->flags & RC_GammaCorrection) && ctx->attribs->rgamma > 0
 180             && ctx->attribs->ggamma > 0 && ctx->attribs->bgamma > 0) {
 181                 double rg, gg, bg;
 182                 double tmp;
 183
 184                 /* do gamma correction */
 185                 rg = 1.0 / ctx->attribs->rgamma;
 186                 gg = 1.0 / ctx->attribs->ggamma;
 187                 bg = 1.0 / ctx->attribs->bgamma;
 188                 for (r = 0; r < cpc; r++) {
 189                         for (g = 0; g < cpc; g++) {
 190                                 for (b = 0; b < cpc; b++) {
 191                                         colors[i].red = (r * 0xffff) / (cpc - 1);
 192                                         colors[i].green = (g * 0xffff) / (cpc - 1);
 193                                         colors[i].blue = (b * 0xffff) / (cpc - 1);
 194                                         colors[i].flags = DoRed | DoGreen | DoBlue;
 195
 196                                         tmp = (double)colors[i].red / 65536.0;
 197                                         colors[i].red = (unsigned short)(65536.0 * pow(tmp, rg));
 198
 199                                         tmp = (double)colors[i].green / 65536.0;
 200                                         colors[i].green = (unsigned short)(65536.0 * pow(tmp, gg));
 201
 202                                         tmp = (double)colors[i].blue / 65536.0;
 203                                         colors[i].blue = (unsigned short)(65536.0 * pow(tmp, bg));
 204
 205                                         i++;
 206                                 }
 207                         }
 208                 }
 209
 210         } else {
 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                                         i++;
 219                                 }
 220                         }
 221                 }
 222         }
 223         /* try to allocate the colors */
 224         for (i = 0; i < ncolors; i++) {
 225                 if (!XAllocColor(ctx->dpy, ctx->cmap, &(colors[i]))) {
 226                         colors[i].flags = 0;    /* failed */
 227                 } else {
 228                         colors[i].flags = DoRed | DoGreen | DoBlue;
 229                 }
 230         }
 231         /* try to allocate close values for the colors that couldn't
 232          * be allocated before */
 233         avncolors = (1 << ctx->depth > 256 ? 256 : 1 << ctx->depth);
 234         for (i = 0; i < avncolors; i++)
 235                 avcolors[i].pixel = i;
 236
 237         XQueryColors(ctx->dpy, ctx->cmap, avcolors, avncolors);
 238
 239         for (i = 0; i < ncolors; i++) {
 240                 if (colors[i].flags == 0) {
 241                         int j;
 242                         unsigned long cdiff = 0xffffffff, diff;
 243                         unsigned long closest = 0;
 244
 245                         retries = 2;
 246
 247                         while (retries--) {
 248                                 /* find closest color */
 249                                 for (j = 0; j < avncolors; j++) {
 250                                         r = (colors[i].red - avcolors[i].red) >> 8;
 251                                         g = (colors[i].green - avcolors[i].green) >> 8;
 252                                         b = (colors[i].blue - avcolors[i].blue) >> 8;
 253                                         diff = r * r + g * g + b * b;
 254                                         if (diff < cdiff) {
 255                                                 cdiff = diff;
 256                                                 closest = j;
 257                                         }
 258                                 }
 259                                 /* allocate closest color found */
 260                                 colors[i].red = avcolors[closest].red;
 261                                 colors[i].green = avcolors[closest].green;
 262                                 colors[i].blue = avcolors[closest].blue;
 263                                 if (XAllocColor(ctx->dpy, ctx->cmap, &colors[i])) {
 264                                         colors[i].flags = DoRed | DoGreen | DoBlue;
 265                                         break;  /* succeeded, don't need to retry */
 266                                 }
 267 #ifdef WRLIB_DEBUG
 268                                 fputs("close color allocation failed. Retrying...\n", stderr);
 269 #endif
 270                         }
 271                 }
 272         }
 273
 274         ctx->colors = colors;
 275         ctx->ncolors = ncolors;
 276
 277         /* fill the pixels shortcut array */
 278         for (i = 0; i < ncolors; i++) {
 279                 ctx->pixels[i] = ctx->colors[i].pixel;
 280         }
 281
 282         return True;
 283 }
 284
 285 static XColor *allocateGrayScale(RContext * ctx)
 286 {
 287         XColor *colors;
 288         XColor avcolors[256];
 289         int avncolors;
 290         int i, ncolors, r, g, b;
 291         int retries;
 292         int cpc = ctx->attribs->colors_per_channel;
 293
 294         ncolors = cpc * cpc * cpc;
 295
 296         if (ctx->vclass == StaticGray) {
 297                 /* we might as well use all grays */
 298                 ncolors = 1 << ctx->depth;
 299         } else {
 300                 if (ncolors > (1 << ctx->depth)) {
 301                         /* reduce colormap size */
 302                         cpc = ctx->attribs->colors_per_channel = 1 << ((int)ctx->depth / 3);
 303                         ncolors = cpc * cpc * cpc;
 304                 }
 305
 306                 assert(cpc >= 2 && ncolors <= (1 << ctx->depth));
 307         }
 308
 309         if (ncolors >= 256 && ctx->vclass == StaticGray) {
 310                 /* don't need dithering for 256 levels of gray in StaticGray visual */
 311                 ctx->attribs->render_mode = RBestMatchRendering;
 312         }
 313
 314         colors = malloc(sizeof(XColor) * ncolors);
 315         if (!colors) {
 316                 RErrorCode = RERR_NOMEMORY;
 317                 return False;
 318         }
 319         for (i = 0; i < ncolors; i++) {
 320                 colors[i].red = (i * 0xffff) / (ncolors - 1);
 321                 colors[i].green = (i * 0xffff) / (ncolors - 1);
 322                 colors[i].blue = (i * 0xffff) / (ncolors - 1);
 323                 colors[i].flags = DoRed | DoGreen | DoBlue;
 324         }
 325         /* try to allocate the colors */
 326         for (i = 0; i < ncolors; i++) {
 327 #ifdef WRLIB_DEBUG
 328                 fprintf(stderr, "trying:%x,%x,%x\n", colors[i].red, colors[i].green, colors[i].blue);
 329 #endif
 330                 if (!XAllocColor(ctx->dpy, ctx->cmap, &(colors[i]))) {
 331                         colors[i].flags = 0;    /* failed */
 332 #ifdef WRLIB_DEBUG
 333                         fprintf(stderr, "failed:%x,%x,%x\n", colors[i].red, colors[i].green, colors[i].blue);
 334 #endif
 335                 } else {
 336                         colors[i].flags = DoRed | DoGreen | DoBlue;
 337 #ifdef WRLIB_DEBUG
 338                         fprintf(stderr, "success:%x,%x,%x\n", colors[i].red, colors[i].green, colors[i].blue);
 339 #endif
 340                 }
 341         }
 342         /* try to allocate close values for the colors that couldn't
 343          * be allocated before */
 344         avncolors = (1 << ctx->depth > 256 ? 256 : 1 << ctx->depth);
 345         for (i = 0; i < avncolors; i++)
 346                 avcolors[i].pixel = i;
 347
 348         XQueryColors(ctx->dpy, ctx->cmap, avcolors, avncolors);
 349
 350         for (i = 0; i < ncolors; i++) {
 351                 if (colors[i].flags == 0) {
 352                         int j;
 353                         unsigned long cdiff = 0xffffffff, diff;
 354                         unsigned long closest = 0;
 355
 356                         retries = 2;
 357
 358                         while (retries--) {
 359                                 /* find closest color */
 360                                 for (j = 0; j < avncolors; j++) {
 361                                         r = (colors[i].red - avcolors[i].red) >> 8;
 362                                         g = (colors[i].green - avcolors[i].green) >> 8;
 363                                         b = (colors[i].blue - avcolors[i].blue) >> 8;
 364                                         diff = r * r + g * g + b * b;
 365                                         if (diff < cdiff) {
 366                                                 cdiff = diff;
 367                                                 closest = j;
 368                                         }
 369                                 }
 370                                 /* allocate closest color found */
 371 #ifdef WRLIB_DEBUG
 372                                 fprintf(stderr, "best match:%x,%x,%x => %x,%x,%x\n",
 373                                         colors[i].red, colors[i].green, colors[i].blue,
 374                                         avcolors[closest].red, avcolors[closest].green, avcolors[closest].blue);
 375 #endif
 376                                 colors[i].red = avcolors[closest].red;
 377                                 colors[i].green = avcolors[closest].green;
 378                                 colors[i].blue = avcolors[closest].blue;
 379                                 if (XAllocColor(ctx->dpy, ctx->cmap, &colors[i])) {
 380                                         colors[i].flags = DoRed | DoGreen | DoBlue;
 381                                         break;  /* succeeded, don't need to retry */
 382                                 }
 383 #ifdef WRLIB_DEBUG
 384                                 fputs("close color allocation failed. Retrying...\n", stderr);
 385 #endif
 386                         }
 387                 }
 388         }
 389         return colors;
 390 }
 391
 392 static Bool setupPseudoColorColormap(RContext * context)
 393 {
 394         Atom property = 0;
 395
 396         if (context->attribs->standard_colormap_mode == RCreateStdColormap) {
 397                 property = XInternAtom(context->dpy, "RGB_DEFAULT_MAP", False);
 398
 399                 if (!setupStandardColormap(context, property)) {
 400                         return False;
 401                 }
 402         }
 403
 404         if (context->attribs->standard_colormap_mode != RIgnoreStdColormap) {
 405                 XStandardColormap *maps;
 406                 int count, i;
 407
 408                 if (!property) {
 409                         property = XInternAtom(context->dpy, "RGB_BEST_MAP", False);
 410                         if (!XGetRGBColormaps(context->dpy,
 411                                               DefaultRootWindow(context->dpy), &maps, &count, property)) {
 412                                 maps = NULL;
 413                         }
 414
 415                         if (!maps) {
 416                                 property = XInternAtom(context->dpy, "RGB_DEFAULT_MAP", False);
 417                                 if (!XGetRGBColormaps(context->dpy,
 418                                                       DefaultRootWindow(context->dpy), &maps, &count, property)) {
 419                                         maps = NULL;
 420                                 }
 421                         }
 422                 } else {
 423                         if (!XGetRGBColormaps(context->dpy,
 424                                               DefaultRootWindow(context->dpy), &maps, &count, property)) {
 425                                 maps = NULL;
 426                         }
 427                 }
 428
 429                 if (maps) {
 430                         int theMap = -1;
 431
 432                         for (i = 0; i < count; i++) {
 433                                 if (maps[i].visualid == context->visual->visualid) {
 434                                         theMap = i;
 435                                         break;
 436                                 }
 437                         }
 438
 439                         if (theMap < 0) {
 440                                 puts("wrlib: no std cmap found");
 441                         }
 442
 443                         if (theMap >= 0 && allocateStandardPseudoColor(context, &maps[theMap])) {
 444
 445                                 context->std_rgb_map = XAllocStandardColormap();
 446
 447                                 *context->std_rgb_map = maps[theMap];
 448
 449                                 context->cmap = context->std_rgb_map->colormap;
 450
 451                                 XFree(maps);
 452
 453                                 return True;
 454                         }
 455
 456                         XFree(maps);
 457                 }
 458         }
 459
 460         context->attribs->standard_colormap_mode = RIgnoreStdColormap;
 461
 462         /* RIgnoreStdColormap and fallback */
 463         return allocatePseudoColor(context);
 464 }
 465
 466 static char *mygetenv(const char *var, int scr)
 467 {
 468         char *p;
 469         char varname[64];
 470
 471         snprintf(varname, sizeof(varname), "%s%i", var, scr);
 472         p = getenv(varname);
 473         if (!p) {
 474                 p = getenv(var);
 475         }
 476         return p;
 477 }
 478
 479 static void gatherconfig(RContext * context, int screen_n)
 480 {
 481         char *ptr;
 482
 483         ptr = mygetenv("WRASTER_GAMMA", screen_n);
 484         if (ptr) {
 485                 float g1, g2, g3;
 486                 if (sscanf(ptr, "%f/%f/%f", &g1, &g2, &g3) != 3 || g1 <= 0.0 || g2 <= 0.0 || g3 <= 0.0) {
 487                         printf("wrlib: invalid value(s) for gamma correction \"%s\"\n", ptr);
 488                 } else {
 489                         context->attribs->flags |= RC_GammaCorrection;
 490                         context->attribs->rgamma = g1;
 491                         context->attribs->ggamma = g2;
 492                         context->attribs->bgamma = g3;
 493                 }
 494         }
 495         ptr = mygetenv("WRASTER_COLOR_RESOLUTION", screen_n);
 496         if (ptr) {
 497                 int i;
 498                 if (sscanf(ptr, "%d", &i) != 1 || i < 2 || i > 6) {
 499                         printf("wrlib: invalid value for color resolution \"%s\"\n", ptr);
 500                 } else {
 501                         context->attribs->flags |= RC_ColorsPerChannel;
 502                         context->attribs->colors_per_channel = i;
 503                 }
 504         }
 505 }
 506
 507 static void getColormap(RContext * context, int screen_number)
 508 {
 509         Colormap cmap = None;
 510         XStandardColormap *cmaps;
 511         int ncmaps, i;
 512
 513         if (XGetRGBColormaps(context->dpy,
 514                              RootWindow(context->dpy, screen_number), &cmaps, &ncmaps, XA_RGB_DEFAULT_MAP)) {
 515                 for (i = 0; i < ncmaps; ++i) {
 516                         if (cmaps[i].visualid == context->visual->visualid) {
 517                                 cmap = cmaps[i].colormap;
 518                                 break;
 519                         }
 520                 }
 521                 XFree(cmaps);
 522         }
 523         if (cmap == None) {
 524                 XColor color;
 525
 526                 cmap = XCreateColormap(context->dpy,
 527                                        RootWindow(context->dpy, screen_number), context->visual, AllocNone);
 528
 529                 color.red = color.green = color.blue = 0;
 530                 XAllocColor(context->dpy, cmap, &color);
 531                 context->black = color.pixel;
 532
 533                 color.red = color.green = color.blue = 0xffff;
 534                 XAllocColor(context->dpy, cmap, &color);
 535                 context->white = color.pixel;
 536
 537         }
 538         context->cmap = cmap;
 539 }
 540
 541 static int count_offset(unsigned long mask)
 542 {
 543         int i;
 544
 545         i = 0;
 546         while ((mask & 1) == 0) {
 547                 i++;
 548                 mask = mask >> 1;
 549         }
 550         return i;
 551 }
 552
 553 RContext *RCreateContext(Display * dpy, int screen_number, const RContextAttributes * attribs)
 554 {
 555         RContext *context;
 556         XGCValues gcv;
 557
 558         context = malloc(sizeof(RContext));
 559         if (!context) {
 560                 RErrorCode = RERR_NOMEMORY;
 561                 return NULL;
 562         }
 563         memset(context, 0, sizeof(RContext));
 564
 565         context->dpy = dpy;
 566
 567         context->screen_number = screen_number;
 568
 569         context->attribs = malloc(sizeof(RContextAttributes));
 570         if (!context->attribs) {
 571                 free(context);
 572                 RErrorCode = RERR_NOMEMORY;
 573                 return NULL;
 574         }
 575         if (!attribs)
 576                 *context->attribs = DEFAULT_CONTEXT_ATTRIBS;
 577         else
 578                 *context->attribs = *attribs;
 579
 580         if (!(context->attribs->flags & RC_StandardColormap)) {
 581                 context->attribs->standard_colormap_mode = RUseStdColormap;
 582         }
 583
 584         if (!(context->attribs->flags & RC_ScalingFilter)) {
 585                 context->attribs->flags |= RC_ScalingFilter;
 586                 context->attribs->scaling_filter = RMitchellFilter;
 587         }
 588
 589         /* get configuration from environment variables */
 590         gatherconfig(context, screen_number);
 591         _wraster_change_filter(context->attribs->scaling_filter);
 592         if ((context->attribs->flags & RC_VisualID)) {
 593                 XVisualInfo *vinfo, templ;
 594                 int nret;
 595
 596                 templ.screen = screen_number;
 597                 templ.visualid = context->attribs->visualid;
 598                 vinfo = XGetVisualInfo(context->dpy, VisualIDMask | VisualScreenMask, &templ, &nret);
 599                 if (!vinfo || nret == 0) {
 600                         free(context);
 601                         RErrorCode = RERR_BADVISUALID;
 602                         return NULL;
 603                 }
 604
 605                 if (vinfo[0].visual == DefaultVisual(dpy, screen_number)) {
 606                         context->attribs->flags |= RC_DefaultVisual;
 607                 } else {
 608                         XSetWindowAttributes attr;
 609                         unsigned long mask;
 610
 611                         context->visual = vinfo[0].visual;
 612                         context->depth = vinfo[0].depth;
 613                         context->vclass = vinfo[0].class;
 614                         getColormap(context, screen_number);
 615                         attr.colormap = context->cmap;
 616                         attr.override_redirect = True;
 617                         attr.border_pixel = 0;
 618                         attr.background_pixel = 0;
 619                         mask = CWBorderPixel | CWColormap | CWOverrideRedirect | CWBackPixel;
 620                         context->drawable =
 621                             XCreateWindow(dpy, RootWindow(dpy, screen_number), 1, 1,
 622                                           1, 1, 0, context->depth, CopyFromParent, context->visual, mask, &attr);
 623                 }
 624                 XFree(vinfo);
 625         }
 626
 627         /* use default */
 628         if (!context->visual) {
 629                 if ((context->attribs->flags & RC_DefaultVisual)
 630                     || !bestContext(dpy, screen_number, context)) {
 631                         context->visual = DefaultVisual(dpy, screen_number);
 632                         context->depth = DefaultDepth(dpy, screen_number);
 633                         context->cmap = DefaultColormap(dpy, screen_number);
 634                         context->drawable = RootWindow(dpy, screen_number);
 635                         context->black = BlackPixel(dpy, screen_number);
 636                         context->white = WhitePixel(dpy, screen_number);
 637                         context->vclass = context->visual->class;
 638                 }
 639         }
 640
 641         gcv.function = GXcopy;
 642         gcv.graphics_exposures = False;
 643         context->copy_gc = XCreateGC(dpy, context->drawable, GCFunction | GCGraphicsExposures, &gcv);
 644
 645         if (context->vclass == PseudoColor || context->vclass == StaticColor) {
 646                 if (!setupPseudoColorColormap(context)) {
 647                         free(context);
 648                         return NULL;
 649                 }
 650         } else if (context->vclass == GrayScale || context->vclass == StaticGray) {
 651                 context->colors = allocateGrayScale(context);
 652                 if (!context->colors) {
 653                         free(context);
 654                         return NULL;
 655                 }
 656         } else if (context->vclass == TrueColor) {
 657                 /* calc offsets to create a TrueColor pixel */
 658                 context->red_offset = count_offset(context->visual->red_mask);
 659                 context->green_offset = count_offset(context->visual->green_mask);
 660                 context->blue_offset = count_offset(context->visual->blue_mask);
 661                 /* disable dithering on 24 bits visuals */
 662                 if (context->depth >= 24)
 663                         context->attribs->render_mode = RBestMatchRendering;
 664         }
 665
 666         /* check avaiability of MIT-SHM */
 667 #ifdef XSHM
 668         if (!(context->attribs->flags & RC_UseSharedMemory)) {
 669                 context->attribs->flags |= RC_UseSharedMemory;
 670                 context->attribs->use_shared_memory = True;
 671         }
 672
 673         if (context->attribs->use_shared_memory) {
 674                 int major, minor;
 675                 Bool sharedPixmaps;
 676
 677                 context->flags.use_shared_pixmap = 0;
 678
 679                 if (!XShmQueryVersion(context->dpy, &major, &minor, &sharedPixmaps)) {
 680                         context->attribs->use_shared_memory = False;
 681                 } else {
 682                         if (XShmPixmapFormat(context->dpy) == ZPixmap)
 683                                 context->flags.use_shared_pixmap = sharedPixmaps;
 684                 }
 685         }
 686 #endif
 687
 688         return context;
 689 }
 690
 691 static Bool bestContext(Display * dpy, int screen_number, RContext * context)
 692 {
 693         XVisualInfo *vinfo = NULL, rvinfo;
 694         int best = -1, numvis, i;
 695         long flags;
 696         XSetWindowAttributes attr;
 697
 698         rvinfo.class = TrueColor;
 699         rvinfo.screen = screen_number;
 700         flags = VisualClassMask | VisualScreenMask;
 701
 702         vinfo = XGetVisualInfo(dpy, flags, &rvinfo, &numvis);
 703         if (vinfo) {            /* look for a TrueColor, 24-bit or more (pref 24) */
 704                 for (i = numvis - 1, best = -1; i >= 0; i--) {
 705                         if (vinfo[i].depth == 24)
 706                                 best = i;
 707                         else if (vinfo[i].depth > 24 && best < 0)
 708                                 best = i;
 709                 }
 710         }
 711         if (best > -1) {
 712                 context->visual = vinfo[best].visual;
 713                 context->depth = vinfo[best].depth;
 714                 context->vclass = vinfo[best].class;
 715                 getColormap(context, screen_number);
 716                 attr.colormap = context->cmap;
 717                 attr.override_redirect = True;
 718                 attr.border_pixel = 0;
 719                 context->drawable =
 720                     XCreateWindow(dpy, RootWindow(dpy, screen_number),
 721                                   1, 1, 1, 1, 0, context->depth,
 722                                   CopyFromParent, context->visual,
 723                                   CWBorderPixel | CWColormap | CWOverrideRedirect, &attr);
 724         }
 725         if (vinfo)
 726                 XFree((char *)vinfo);
 727
 728         if (best < 0)
 729                 return False;
 730         else
 731                 return True;
 732 }