summaryrefslogtreecommitdiffstats
path: root/src/mesa/drivers/x11/xmesaP.h
blob: 6a6c9ef6004c63392c0c28bb9983c011da7a077c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
/*
 * Mesa 3-D graphics library
 * Version:  7.1
 *
 * Copyright (C) 1999-2007  Brian Paul   All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */


#ifndef XMESAP_H
#define XMESAP_H


#include "xmesa.h"
#include "main/mtypes.h"
#if defined(FX)
#include "GL/fxmesa.h"
#include "xm_glide.h"
#endif
#ifdef XFree86Server
#include "xm_image.h"
#endif


extern _glthread_Mutex _xmesa_lock;

extern XMesaBuffer XMesaBufferList;

/* for PF_8R8G8B24 pixel format */
typedef struct {
   GLubyte b;
   GLubyte g;
   GLubyte r;
} bgr_t;


struct xmesa_renderbuffer;


/* Function pointer for clearing color buffers */
typedef void (*ClearFunc)( GLcontext *ctx, struct xmesa_renderbuffer *xrb,
                           GLint x, GLint y, GLint width, GLint height );




/** Framebuffer pixel formats */
enum pixel_format {
   PF_Index,		/**< Color Index mode */
   PF_Truecolor,	/**< TrueColor or DirectColor, any depth */
   PF_Dither_True,	/**< TrueColor with dithering */
   PF_8A8R8G8B,		/**< 32-bit TrueColor:  8-A, 8-R, 8-G, 8-B bits */
   PF_8A8B8G8R,		/**< 32-bit TrueColor:  8-A, 8-B, 8-G, 8-R bits */
   PF_8R8G8B,		/**< 32-bit TrueColor:  8-R, 8-G, 8-B bits */
   PF_8R8G8B24,		/**< 24-bit TrueColor:  8-R, 8-G, 8-B bits */
   PF_5R6G5B,		/**< 16-bit TrueColor:  5-R, 6-G, 5-B bits */
   PF_Dither,		/**< Color-mapped RGB with dither */
   PF_Lookup,		/**< Color-mapped RGB without dither */
   PF_HPCR,		/**< HP Color Recovery (ad@lms.be 30/08/95) */
   PF_1Bit,		/**< monochrome dithering of RGB */
   PF_Grayscale,	/**< Grayscale or StaticGray */
   PF_Dither_5R6G5B	/**< 16-bit dithered TrueColor: 5-R, 6-G, 5-B */
};


/**
 * Visual inforation, derived from GLvisual.
 * Basically corresponds to an XVisualInfo.
 */
struct xmesa_visual {
   GLvisual mesa_visual;	/* Device independent visual parameters */
   XMesaDisplay *display;	/* The X11 display */
#ifdef XFree86Server
   GLint ColormapEntries;
   GLint nplanes;
#else
   XMesaVisualInfo visinfo;	/* X's visual info (pointer to private copy) */
   XVisualInfo *vishandle;	/* Only used in fakeglx.c */
#endif
   GLint BitsPerPixel;		/* True bits per pixel for XImages */

   GLboolean ximage_flag;	/* Use XImage for back buffer (not pixmap)? */

   enum pixel_format dithered_pf;  /* Pixel format when dithering */
   enum pixel_format undithered_pf;/* Pixel format when not dithering */

   GLfloat RedGamma;		/* Gamma values, 1.0 is default */
   GLfloat GreenGamma;
   GLfloat BlueGamma;

   /* For PF_TRUECOLOR */
   GLint rshift, gshift, bshift;/* Pixel color component shifts */
   GLubyte Kernel[16];		/* Dither kernel */
   unsigned long RtoPixel[512];	/* RGB to pixel conversion */
   unsigned long GtoPixel[512];
   unsigned long BtoPixel[512];
   GLubyte PixelToR[256];	/* Pixel to RGB conversion */
   GLubyte PixelToG[256];
   GLubyte PixelToB[256];

   /* For PF_HPCR */
   short       hpcr_rgbTbl[3][256];
   GLboolean   hpcr_clear_flag;
   GLubyte     hpcr_clear_ximage_pattern[2][16];
   XMesaImage *hpcr_clear_ximage;
   XMesaPixmap hpcr_clear_pixmap;

   /* For PF_1BIT */
   int bitFlip;
};


/**
 * Context info, derived from GLcontext.
 * Basically corresponds to a GLXContext.
 */
struct xmesa_context {
   GLcontext mesa;		/* the core library context (containment) */
   XMesaVisual xm_visual;	/* Describes the buffers */
   XMesaBuffer xm_buffer;	/* current span/point/line/triangle buffer */

   XMesaDisplay *display;	/* == xm_visual->display */
   GLboolean swapbytes;		/* Host byte order != display byte order? */
   GLboolean direct;		/* Direct rendering context? */

   enum pixel_format pixelformat;

   GLubyte clearcolor[4];		/* current clearing color */
   unsigned long clearpixel;		/* current clearing pixel value */
};


/**
 * Types of X/GLX drawables we might render into.
 */
typedef enum {
   WINDOW,          /* An X window */
   GLXWINDOW,       /* GLX window */
   PIXMAP,          /* GLX pixmap */
   PBUFFER          /* GLX Pbuffer */
} BufferType;


/** Values for db_mode: */
/*@{*/
#define BACK_PIXMAP	1
#define BACK_XIMAGE	2
/*@}*/


/**
 * An xmesa_renderbuffer represents the back or front color buffer.
 * For the front color buffer:
 *    <drawable> is the X window
 * For the back color buffer:
 *    Either <ximage> or <pixmap> will be used, never both.
 * In any case, <drawable> always equals <pixmap>.
 * For stand-alone Mesa, we could merge <drawable> and <pixmap> into one
 * field.  We don't do that for the server-side GLcore module because
 * pixmaps and drawables are different and we'd need a bunch of casts.
 */
struct xmesa_renderbuffer
{
   struct gl_renderbuffer Base;  /* Base class */

   XMesaBuffer Parent;  /**< The XMesaBuffer this renderbuffer belongs to */
   XMesaDrawable drawable;	/* Usually the X window ID */
   XMesaPixmap pixmap;	/* Back color buffer */
   XMesaImage *ximage;	/* The back buffer, if not using a Pixmap */

   GLubyte *origin1;	/* used for PIXEL_ADDR1 macro */
   GLint width1;
   GLushort *origin2;	/* used for PIXEL_ADDR2 macro */
   GLint width2;
   GLubyte *origin3;	/* used for PIXEL_ADDR3 macro */
   GLint width3;
   GLuint *origin4;	/* used for PIXEL_ADDR4 macro */
   GLint width4;

   GLint bottom;	/* used for FLIP macro, equals height - 1 */

   ClearFunc clearFunc;
};


/**
 * Framebuffer information, derived from.
 * Basically corresponds to a GLXDrawable.
 */
struct xmesa_buffer {
   GLframebuffer mesa_buffer;	/* depth, stencil, accum, etc buffers */
				/* This MUST BE FIRST! */
   GLboolean wasCurrent;	/* was ever the current buffer? */
   XMesaVisual xm_visual;	/* the X/Mesa visual */

   XMesaDisplay *display;
   BufferType type;             /* window, pixmap, pbuffer or glxwindow */

   struct xmesa_renderbuffer *frontxrb; /* front color renderbuffer */
   struct xmesa_renderbuffer *backxrb;  /* back color renderbuffer */

   XMesaColormap cmap;		/* the X colormap */

   unsigned long selectedEvents;/* for pbuffers only */

   GLint db_mode;		/* 0 = single buffered */
				/* BACK_PIXMAP = use Pixmap for back buffer */
				/* BACK_XIMAGE = use XImage for back buffer */
   GLboolean swAlpha;

   GLuint shm;			/* X Shared Memory extension status:	*/
				/*    0 = not available			*/
				/*    1 = XImage support available	*/
				/*    2 = Pixmap support available too	*/
#if defined(USE_XSHM) && !defined(XFree86Server)
   XShmSegmentInfo shminfo;
#endif

   XMesaImage *rowimage;	/* Used for optimized span writing */
   XMesaPixmap stipple_pixmap;	/* For polygon stippling */
   XMesaGC stipple_gc;		/* For polygon stippling */

   XMesaGC gc;			/* scratch GC for span, line, tri drawing */
   XMesaGC cleargc;		/* GC for clearing the color buffer */
   XMesaGC swapgc;		/* GC for swapping the color buffers */

   /* The following are here instead of in the XMesaVisual
    * because they depend on the window's colormap.
    */

   /* For PF_DITHER, PF_LOOKUP, PF_GRAYSCALE */
   unsigned long color_table[576];	/* RGB -> pixel value */

   /* For PF_DITHER, PF_LOOKUP, PF_GRAYSCALE */
   GLubyte pixel_to_r[65536];		/* pixel value -> red */
   GLubyte pixel_to_g[65536];		/* pixel value -> green */
   GLubyte pixel_to_b[65536];		/* pixel value -> blue */

   /* Used to do XAllocColor/XFreeColors accounting: */
   int num_alloced;
#if defined(XFree86Server)
   Pixel alloced_colors[256];
#else
   unsigned long alloced_colors[256];
#endif

#if defined( FX )
   /* For 3Dfx Glide only */
   GLboolean FXisHackUsable;	/* Can we render into window? */
   GLboolean FXwindowHack;	/* Are we rendering into a window? */
   fxMesaContext FXctx;
#endif

   /* GLX_EXT_texture_from_pixmap */
   GLint TextureTarget; /** GLX_TEXTURE_1D_EXT, for example */
   GLint TextureFormat; /** GLX_TEXTURE_FORMAT_RGB_EXT, for example */
   GLint TextureMipmap; /** 0 or 1 */

   struct xmesa_buffer *Next;	/* Linked list pointer: */
};


/**
 * If pixelformat==PF_TRUECOLOR:
 */
#define PACK_TRUECOLOR( PIXEL, R, G, B )	\
   PIXEL = xmesa->xm_visual->RtoPixel[R]	\
         | xmesa->xm_visual->GtoPixel[G]	\
         | xmesa->xm_visual->BtoPixel[B];	\


/**
 * If pixelformat==PF_TRUEDITHER:
 */
#define PACK_TRUEDITHER( PIXEL, X, Y, R, G, B )			\
{								\
   int d = xmesa->xm_visual->Kernel[((X)&3) | (((Y)&3)<<2)];	\
   PIXEL = xmesa->xm_visual->RtoPixel[(R)+d]			\
         | xmesa->xm_visual->GtoPixel[(G)+d]			\
         | xmesa->xm_visual->BtoPixel[(B)+d];			\
}



/**
 * If pixelformat==PF_8A8B8G8R:
 */
#define PACK_8A8B8G8R( R, G, B, A )	\
	( ((A) << 24) | ((B) << 16) | ((G) << 8) | (R) )


/**
 * Like PACK_8A8B8G8R() but don't use alpha.  This is usually an acceptable
 * shortcut.
 */
#define PACK_8B8G8R( R, G, B )   ( ((B) << 16) | ((G) << 8) | (R) )



/**
 * If pixelformat==PF_8R8G8B:
 */
#define PACK_8R8G8B( R, G, B)	 ( ((R) << 16) | ((G) << 8) | (B) )


/**
 * If pixelformat==PF_5R6G5B:
 */
#define PACK_5R6G5B( R, G, B)	 ( (((R) & 0xf8) << 8) | (((G) & 0xfc) << 3) | ((B) >> 3) )


/**
 * If pixelformat==PF_8A8R8G8B:
 */
#define PACK_8A8R8G8B( R, G, B, A )	\
	( ((A) << 24) | ((R) << 16) | ((G) << 8) | (B) )



/**
 * If pixelformat==PF_DITHER:
 *
 * Improved 8-bit RGB dithering code contributed by Bob Mercier
 * (mercier@hollywood.cinenet.net).  Thanks Bob!
 */
#ifdef DITHER666
# define DITH_R   6
# define DITH_G   6
# define DITH_B   6
# define DITH_MIX(r,g,b)  (((r) * DITH_G + (g)) * DITH_B + (b))
#else
# define DITH_R	5
# define DITH_G	9
# define DITH_B	5
# define DITH_MIX(r,g,b)  (((g) << 6) | ((b) << 3) | (r))
#endif
#define DITH_DX	4
#define DITH_DY	4
#define DITH_N	(DITH_DX * DITH_DY)

#define _dither(C, c, d)   (((unsigned)((DITH_N * (C - 1) + 1) * c + d)) >> 12)

#define MAXC	256
extern const int xmesa_kernel8[DITH_DY * DITH_DX];

/* Dither for random X,Y */
#define DITHER_SETUP						\
	int __d;						\
	unsigned long *ctable = XMESA_BUFFER(ctx->DrawBuffer)->color_table;

#define DITHER( X, Y, R, G, B )				\
	(__d = xmesa_kernel8[(((Y)&3)<<2) | ((X)&3)],	\
	 ctable[DITH_MIX(_dither(DITH_R, (R), __d),	\
		         _dither(DITH_G, (G), __d),	\
		         _dither(DITH_B, (B), __d))])

/* Dither for random X, fixed Y */
#define XDITHER_SETUP(Y)					\
	int __d;						\
	unsigned long *ctable = XMESA_BUFFER(ctx->DrawBuffer)->color_table;	\
	const int *kernel = &xmesa_kernel8[ ((Y)&3) << 2 ];

#define XDITHER( X, R, G, B )				\
	(__d = kernel[(X)&3],				\
	ctable[DITH_MIX(_dither(DITH_R, (R), __d),	\
		        _dither(DITH_G, (G), __d),	\
		        _dither(DITH_B, (B), __d))])



/*
 * Dithering for flat-shaded triangles.  Precompute all 16 possible
 * pixel values given the triangle's RGB color.  Contributed by Martin Shenk.
 */
#define FLAT_DITHER_SETUP( R, G, B )					\
	GLushort ditherValues[16];					\
	{								\
	   unsigned long *ctable = XMESA_BUFFER(ctx->DrawBuffer)->color_table;	\
	   int msdr = (DITH_N*((DITH_R)-1)+1) * (R);			\
	   int msdg = (DITH_N*((DITH_G)-1)+1) * (G);			\
	   int msdb = (DITH_N*((DITH_B)-1)+1) * (B);			\
	   int i;							\
	   for (i=0;i<16;i++) {						\
	      int k = xmesa_kernel8[i];					\
	      int j = DITH_MIX( (msdr+k)>>12, (msdg+k)>>12, (msdb+k)>>12 );\
	      ditherValues[i] = (GLushort) ctable[j];			\
	   }								\
        }

#define FLAT_DITHER_ROW_SETUP(Y)					\
	GLushort *ditherRow = ditherValues + ( ((Y)&3) << 2);

#define FLAT_DITHER(X)  ditherRow[(X)&3]



/**
 * If pixelformat==PF_LOOKUP:
 */
#define _dither_lookup(C, c)   (((unsigned)((DITH_N * (C - 1) + 1) * c)) >> 12)

#define LOOKUP_SETUP						\
	unsigned long *ctable = XMESA_BUFFER(ctx->DrawBuffer)->color_table

#define LOOKUP( R, G, B )				\
	ctable[DITH_MIX(_dither_lookup(DITH_R, (R)),	\
		        _dither_lookup(DITH_G, (G)),	\
		        _dither_lookup(DITH_B, (B)))]


/**
 * If pixelformat==PF_HPCR:
 *
 *      HP Color Recovery dithering               (ad@lms.be 30/08/95)
 *      HP has on it's 8-bit 700-series computers, a feature called
 *      'Color Recovery'.  This allows near 24-bit output (so they say).
 *      It is enabled by selecting the 8-bit  TrueColor  visual AND
 *      corresponding  colormap (see tkInitWindow) AND doing some special
 *      dither.
 */
extern const short xmesa_HPCR_DRGB[3][2][16];

#define DITHER_HPCR( X, Y, R, G, B )					   \
  ( ((xmesa->xm_visual->hpcr_rgbTbl[0][R] + xmesa_HPCR_DRGB[0][(Y)&1][(X)&15]) & 0xE0)     \
  |(((xmesa->xm_visual->hpcr_rgbTbl[1][G] + xmesa_HPCR_DRGB[1][(Y)&1][(X)&15]) & 0xE0)>>3) \
  | ((xmesa->xm_visual->hpcr_rgbTbl[2][B] + xmesa_HPCR_DRGB[2][(Y)&1][(X)&15])>>6)	   \
  )



/**
 * If pixelformat==PF_1BIT:
 */
extern const int xmesa_kernel1[16];

#define SETUP_1BIT  int bitFlip = xmesa->xm_visual->bitFlip
#define DITHER_1BIT( X, Y, R, G, B )	\
	(( ((int)(R)+(int)(G)+(int)(B)) > xmesa_kernel1[(((Y)&3) << 2) | ((X)&3)] ) ^ bitFlip)



/**
 * If pixelformat==PF_GRAYSCALE:
 */
#define GRAY_RGB( R, G, B )   XMESA_BUFFER(ctx->DrawBuffer)->color_table[((R) + (G) + (B))/3]



/**
 * Converts a GL window Y coord to an X window Y coord:
 */
#define YFLIP(XRB, Y)  ((XRB)->bottom - (Y))


/**
 * Return the address of a 1, 2 or 4-byte pixel in the buffer's XImage:
 * X==0 is left, Y==0 is bottom.
 */
#define PIXEL_ADDR1(XRB, X, Y)  \
   ( (XRB)->origin1 - (Y) * (XRB)->width1 + (X) )

#define PIXEL_ADDR2(XRB, X, Y)  \
   ( (XRB)->origin2 - (Y) * (XRB)->width2 + (X) )

#define PIXEL_ADDR3(XRB, X, Y)  \
   ( (bgr_t *) ( (XRB)->origin3 - (Y) * (XRB)->width3 + 3 * (X) ))

#define PIXEL_ADDR4(XRB, X, Y)  \
   ( (XRB)->origin4 - (Y) * (XRB)->width4 + (X) )



/*
 * External functions:
 */

extern struct xmesa_renderbuffer *
xmesa_new_renderbuffer(GLcontext *ctx, GLuint name, const GLvisual *visual,
                       GLboolean backBuffer);

extern void
xmesa_delete_framebuffer(struct gl_framebuffer *fb);

extern XMesaBuffer
xmesa_find_buffer(XMesaDisplay *dpy, XMesaColormap cmap, XMesaBuffer notThis);

extern unsigned long
xmesa_color_to_pixel( GLcontext *ctx,
                      GLubyte r, GLubyte g, GLubyte b, GLubyte a,
                      GLuint pixelFormat );

extern void
xmesa_get_window_size(XMesaDisplay *dpy, XMesaBuffer b,
                      GLuint *width, GLuint *height);

extern void
xmesa_check_and_update_buffer_size(XMesaContext xmctx, XMesaBuffer drawBuffer);

extern void
xmesa_init_driver_functions( XMesaVisual xmvisual,
                             struct dd_function_table *driver );

extern void
xmesa_update_state( GLcontext *ctx, GLbitfield new_state );

extern void
xmesa_set_renderbuffer_funcs(struct xmesa_renderbuffer *xrb,
                             enum pixel_format pixelformat, GLint depth);

extern void
xmesa_destroy_buffers_on_display(XMesaDisplay *dpy);


/**
 * Using a function instead of an ordinary cast is safer.
 */
static INLINE struct xmesa_renderbuffer *
xmesa_renderbuffer(struct gl_renderbuffer *rb)
{
   return (struct xmesa_renderbuffer *) rb;
}


/**
 * Return pointer to XMesaContext corresponding to a Mesa GLcontext.
 * Since we're using structure containment, it's just a cast!.
 */
static INLINE XMesaContext
XMESA_CONTEXT(GLcontext *ctx)
{
   return (XMesaContext) ctx;
}


/**
 * Return pointer to XMesaBuffer corresponding to a Mesa GLframebuffer.
 * Since we're using structure containment, it's just a cast!.
 */
static INLINE XMesaBuffer
XMESA_BUFFER(GLframebuffer *b)
{
   return (XMesaBuffer) b;
}


/* Plugged into the software rasterizer.  Try to use internal
 * swrast-style point, line and triangle functions.
 */
extern void xmesa_choose_point( GLcontext *ctx );
extern void xmesa_choose_line( GLcontext *ctx );
extern void xmesa_choose_triangle( GLcontext *ctx );


extern void xmesa_register_swrast_functions( GLcontext *ctx );



#define ENABLE_EXT_texure_compression_s3tc 0 /* SW texture compression */

#ifdef XFree86Server
#define ENABLE_EXT_timer_query 0
#elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
#define ENABLE_EXT_timer_query 1 /* should have 64-bit GLuint64EXT */
#else
#define ENABLE_EXT_timer_query 0 /* may not have 64-bit GLuint64EXT */
#endif

#endif