xref: /haiku/src/add-ons/accelerants/nvidia/Overlay.c (revision 2b76973fa2401f7a5edf68e6470f3d3210cbcff3)
1 /* Written by Rudolf Cornelissen 05/2002-5/2009 */
2 
3 /* Note on 'missing features' in BeOS 5.0.3 and DANO:
4  * BeOS needs to define more colorspaces! It would be nice if BeOS would support the FourCC 'definitions'
5  * of colorspaces. These colorspaces are 32bit words, so it could be simply done (or is it already so?)
6  */
7 
8 #define MODULE_BIT 0x00000400
9 
10 #include "acc_std.h"
11 
12 /* define the supported overlay input colorspaces */
13 /* It would be nice to have the YUV4:2:0 2-plane mode implemented also later on, but the Be colorspace
14  * definitions (in GraphicsDefs.h, R5.0.3 and DANO5.1d0) do not include this one... */
15 static uint32 overlay_colorspaces [] = { (uint32)B_YCbCr422, (uint32)B_NO_COLOR_SPACE };
16 
17 uint32 OVERLAY_COUNT(const display_mode *dm)
18 // This method is never used AFAIK though it *is* exported on R5.0.3 and DANO.
19 // Does someone know howto invoke it?
20 {
21 	LOG(4,("Overlay: count called\n"));
22 
23 	/* check for NULL pointer */
24 	if (dm == NULL)
25 	{
26 		LOG(4,("Overlay: No display mode specified!\n"));
27 	}
28 	/* apparantly overlay count should report the number of 'overlay units' on the card */
29 	return 1;
30 }
31 
32 const uint32 *OVERLAY_SUPPORTED_SPACES(const display_mode *dm)
33 // This method is never used AFAIK though it *is* exported on R5.0.3 and DANO.
34 // Does someone know howto invoke it?
35 {
36 	LOG(4,("Overlay: supported_spaces called.\n"));
37 
38 	/* check for NULL pointer */
39 	if (dm == NULL)
40 	{
41 		LOG(4,("Overlay: No display mode specified!\n"));
42 		return NULL;
43 	}
44 
45 	/* assuming interlaced VGA is not supported */
46 	if (dm->timing.flags & B_TIMING_INTERLACED)
47 	{
48 		return NULL;
49 	}
50 	/* return a B_NO_COLOR_SPACE terminated list */
51 	return &overlay_colorspaces[0];
52 }
53 
54 uint32 OVERLAY_SUPPORTED_FEATURES(uint32 a_color_space)
55 // This method is never used AFAIK. On R5.0.3 and DANO it is not even exported!
56 {
57 	LOG(4,("Overlay: supported_features: color_space $%08x\n",a_color_space));
58 
59 	/* check what features are supported for the current overlaybitmap colorspace */
60 	switch (a_color_space)
61 	{
62 	default:
63 			return
64 				( B_OVERLAY_KEYING_USES_ALPHA 	 |
65 				  B_OVERLAY_COLOR_KEY 			 |
66 				  B_OVERLAY_HORIZONTAL_FILTERING |
67 				  B_OVERLAY_VERTICAL_FILTERING );
68 	}
69 }
70 
71 const overlay_buffer *ALLOCATE_OVERLAY_BUFFER(color_space cs, uint16 width, uint16 height)
72 {
73 	int offset = 0;					/* used to determine next buffer to create */
74 	uint32 adress, adress2, temp32;	/* used to calculate buffer adresses */
75 	uint32 oldsize = 0;				/* used to 'squeeze' new buffers between already existing ones */
76 	int cnt;						/* loopcounter */
77 
78 	/* acquire the shared benaphore */
79 	AQUIRE_BEN(si->overlay.lock)
80 
81 	LOG(4,("Overlay: cardRAM_start = $%08x\n",(uint32)((uint8*)si->framebuffer)));
82 	LOG(4,("Overlay: cardRAM_start_DMA = $%08x\n",(uint32)((uint8*)si->framebuffer_pci)));
83 	LOG(4,("Overlay: cardRAM_size = %3.3fMb\n",(si->ps.memory_size / (1024.0 * 1024.0))));
84 
85 	/* find first empty slot (room for another buffer?) */
86 	for (offset = 0; offset < MAXBUFFERS; offset++)
87 	{
88 		if (si->overlay.myBuffer[offset].buffer == NULL) break;
89 	}
90 
91 	LOG(4,("Overlay: Allocate_buffer offset = %d\n",offset));
92 
93 	if (offset < MAXBUFFERS)
94 	/* setup new scaler input buffer */
95 	{
96 		switch (cs)
97 		{
98 			case B_YCbCr422:
99 					if (si->ps.card_arch < NV10A)
100 					{
101 						/* check if slopspace is needed: RIVA128 and TNT need ~0x000f. */
102 						si->overlay.myBuffer[offset].width = ((width + 0x000f) & ~0x000f);
103 					}
104 					else
105 					{
106 						/* check if slopspace is needed: GeForce need ~0x001f. */
107 						/* fixme:
108 						 * update needed for GF DVDmax support to adhere to CRTC2 constraints?? */
109 						si->overlay.myBuffer[offset].width = ((width + 0x001f) & ~0x001f);
110 					}
111 					si->overlay.myBuffer[offset].bytes_per_row = 2 * si->overlay.myBuffer[offset].width;
112 
113 					/* check if the requested horizontal pitch is supported: */
114 					//fixme: tune for GF and TNT...
115 					if (si->overlay.myBuffer[offset].width > 4088)
116 					{
117 						LOG(4,("Overlay: Sorry, requested buffer pitch not supported, aborted\n"));
118 
119 						/* release the shared benaphore */
120 						RELEASE_BEN(si->overlay.lock)
121 
122 						return NULL;
123 					}
124 					break;
125 			default:
126 					/* unsupported colorspace! */
127 					LOG(4,("Overlay: Sorry, colorspace $%08x not supported, aborted\n",cs));
128 
129 					/* release the shared benaphore */
130 					RELEASE_BEN(si->overlay.lock)
131 
132 					return NULL;
133 					break;
134 		}
135 
136 		/* checkout input picture size */
137 		switch (si->ps.card_arch) {
138 		case NV04A:
139 			/* all DVD's are OK, but HDTV 1280x720p is not: it displays ghost images
140 			 * (still find exact limit..) */
141 
142 			/* check if the requested buffer width is supported */
143 			if (si->overlay.myBuffer[offset].width > 1024) {
144 				LOG(4,("Overlay: Sorry, requested buffer width not supported, aborted\n"));
145 
146 				/* release the shared benaphore */
147 				RELEASE_BEN(si->overlay.lock)
148 				return NULL;
149 			}
150 			/* check if the requested buffer height is supported */
151 			if (height > 1024) {
152 				LOG(4,("Overlay: Sorry, requested buffer height not supported, aborted\n"));
153 
154 				/* release the shared benaphore */
155 				RELEASE_BEN(si->overlay.lock)
156 				return NULL;
157 			}
158 			break;
159 		default:
160 			/* HDTV 1920x1080p is confirmed OK on NV11 and higher cards */
161 
162 			/* check if the requested buffer width is supported */
163 			if (si->overlay.myBuffer[offset].width > 1920) {
164 				LOG(4,("Overlay: Sorry, requested buffer width not supported, aborted\n"));
165 
166 				/* release the shared benaphore */
167 				RELEASE_BEN(si->overlay.lock)
168 				return NULL;
169 			}
170 			/* check if the requested buffer height is supported */
171 			if (height > 1080) {
172 				LOG(4,("Overlay: Sorry, requested buffer height not supported, aborted\n"));
173 
174 				/* release the shared benaphore */
175 				RELEASE_BEN(si->overlay.lock)
176 				return NULL;
177 			}
178 			break;
179 		}
180 
181 		/* store slopspace (in pixels) for each bitmap for use by 'overlay unit' (BES) */
182 		si->overlay.myBufInfo[offset].slopspace = si->overlay.myBuffer[offset].width - width;
183 
184 		si->overlay.myBuffer[offset].space = cs;
185 		si->overlay.myBuffer[offset].height = height;
186 
187 		/* we define the overlay buffers to reside 'in the back' of the cards RAM */
188 		/* NOTE to app programmers:
189 		 * Beware that an app using overlay needs to track workspace switches and screenprefs
190 		 * changes. If such an action is detected, the app needs to reset it's pointers to the
191 		 * newly created overlay bitmaps, which will be assigned by BeOS automatically after such
192 		 * an event. (Also the app needs to respect the new overlay_constraints that will be applicable!)
193 		 *
194 		 * It is entirely possible that new bitmaps may *not* be re-setup at all, or less of them
195 		 * than previously setup by the app might be re-setup. This is due to cardRAM restraints then.
196 		 * This means that the app should also check for NULL pointers returned by the bitmaps,
197 		 * and if this happens, it needs to fallback to single buffered overlay or even fallback to
198 		 * bitmap output for the new situation. */
199 
200 		/* Another NOTE for app programmers:
201 		 * A *positive* side-effect of assigning the first overlay buffer exactly at the end of the
202 		 * cardRAM is that apps that try to write beyond the buffer's space get a segfault immediately.
203 		 * This *greatly* simplifies tracking such errors!
204 		 * Of course such errors may lead to strange effects in the app or driver behaviour if they are
205 		 * not hunted down and removed.. */
206 
207 		/* calculate first free RAM adress in card:
208 		 * Driver setup is as follows:
209 		 * card base: 		- hardware cursor bitmap (if used),
210 		 * directly above	- screen memory for both heads */
211 		adress2 = (((uint32)((uint8*)si->fbc.frame_buffer)) +	/* cursor already included here */
212 			(si->fbc.bytes_per_row * si->dm.virtual_height));	/* size in bytes of screen(s) */
213 		LOG(4,("Overlay: first free cardRAM virtual adress $%08x\n", adress2));
214 
215 		/* calculate 'preliminary' buffer size including slopspace */
216 		oldsize = si->overlay.myBufInfo[offset].size;
217 		si->overlay.myBufInfo[offset].size =
218 			si->overlay.myBuffer[offset].bytes_per_row * si->overlay.myBuffer[offset].height;
219 
220 		/* calculate virtual memory adress that would be needed for a new bitmap */
221 		/* NOTE to app programmers:
222 		 * For testing app behaviour regarding workspace switches or screen prefs changes to settings
223 		 * that do not have enough cardRAM left for allocation of overlay bitmaps, you need a card with
224 		 * a low amount of RAM. Or you can set in the file nv.settings for example:
225 		 * memory 8 #8Mb RAM on card
226 		 * and reboot (this simulates 8Mb RAM on the card).
227 		 *
228 		 * If you switch now to settings: 1600x1200x32bit (single head) the app needs to fallback to
229 		 * bitmap output or maybe single buffered overlay output if small bitmaps are used. */
230 
231 		adress = (((uint32)((uint8*)si->framebuffer)) + si->ps.memory_size);
232 		/* Keep some extra distance as a workaround for certain bugs (see
233 		 * DriverInterface.h for an explanation). */
234 		if (si->ps.card_arch < NV40A)
235 			adress -= PRE_NV40_OFFSET;
236 		else
237 			adress -= NV40_PLUS_OFFSET;
238 
239 		for (cnt = 0; cnt <= offset; cnt++)
240 		{
241 			adress -= si->overlay.myBufInfo[cnt].size;
242 		}
243 
244 		/* the > G200 scalers require buffers to be aligned to 16 byte pages cardRAM offset, G200 can do with
245 		 * 8 byte pages cardRAM offset. Compatible settings used, has no real downside consequences here */
246 
247 		/* Check if we need to modify the buffers starting adress and thus the size */
248 		/* calculate 'would be' cardRAM offset */
249 		temp32 = (adress - ((uint32)((vuint32 *)si->framebuffer)));
250 		/* check if it is aligned */
251 		if (temp32 != (temp32 & 0xfffffff0))
252 		{
253 			/* update the (already calculated) buffersize to get it aligned */
254 			si->overlay.myBufInfo[offset].size += (temp32 - (temp32 & 0xfffffff0));
255 			/* update the (already calculated) adress to get it aligned */
256 			adress -= (temp32 - (temp32 & 0xfffffff0));
257 		}
258 		LOG(4,("Overlay: new buffer needs virtual adress $%08x\n", adress));
259 
260 		/* First check now if buffer to be defined is 'last one' in memory (speaking backwards):
261 		 * this is done to prevent a large buffer getting created in the space a small buffer
262 		 * occupied earlier, if not all buffers created were deleted.
263 		 * Note also that the app can delete the buffers in any order desired. */
264 
265 		/* NOTE to app programmers:
266 		 * If you are going to delete a overlay buffer you created, you should delete them *all* and
267 		 * then re-create only the new ones needed. This way you are sure not to get unused memory-
268 		 * space in between your overlay buffers for instance, so cardRAM is used 'to the max'.
269 		 * If you don't, you might not get a buffer at all if you are trying to set up a larger one
270 		 * than before.
271 		 * (Indeed: not all buffers *have* to be of the same type and size...) */
272 
273 		for (cnt = offset; cnt < MAXBUFFERS; cnt++)
274 		{
275 			if (si->overlay.myBuffer[cnt].buffer != NULL)
276 			{
277 				/* Check if the new buffer would fit into the space the single old one used here */
278 				if (si->overlay.myBufInfo[offset].size <= oldsize)
279 				{
280 					/* It does, so we reset to the old size and adresses to prevent the space from shrinking
281 					 * if we get here again... */
282 					adress -= (oldsize - si->overlay.myBufInfo[offset].size);
283 					si->overlay.myBufInfo[offset].size = oldsize;
284 					LOG(4,("Overlay: 'squeezing' in buffer:\n"
285 						   "Overlay: resetting it to virtual adress $%08x and size $%08x\n", adress,oldsize));
286 					/* force exiting the FOR loop */
287 					cnt = MAXBUFFERS;
288 				}
289 				else
290 				{
291 					/* nogo, sorry */
292 					LOG(4,("Overlay: Other buffer(s) exist after this one:\n"
293 						   "Overlay: not enough space to 'squeeze' this one in, aborted\n"));
294 
295 					/* Reset to the old size to prevent the space from 'growing' if we get here again... */
296 					si->overlay.myBufInfo[offset].size = oldsize;
297 
298 					/* release the shared benaphore */
299 					RELEASE_BEN(si->overlay.lock)
300 
301 					return NULL;
302 				}
303 			}
304 		}
305 
306 		/* check if we have enough space to setup this new bitmap
307 		 * (preventing overlap of desktop RAMspace & overlay bitmap RAMspace here) */
308 		if (adress < adress2)
309 		/* nope, sorry */
310 		{
311 			LOG(4,("Overlay: Sorry, no more space for buffers: aborted\n"));
312 
313 			/* release the shared benaphore */
314 			RELEASE_BEN(si->overlay.lock)
315 
316 			return NULL;
317 		}
318 		/* continue buffer setup */
319 		si->overlay.myBuffer[offset].buffer = (void *) adress;
320 
321 		/* calculate physical memory adress (for dma use) */
322 		adress = (((uint32)((uint8*)si->framebuffer_pci)) + si->ps.memory_size);
323 		/* Keep some extra distance as a workaround for certain bugs (see
324 		 * DriverInterface.h for an explanation). */
325 		if (si->ps.card_arch < NV40A)
326 			adress -= PRE_NV40_OFFSET;
327 		else
328 			adress -= NV40_PLUS_OFFSET;
329 
330 		for (cnt = 0; cnt <= offset; cnt++)
331 		{
332 			adress -= si->overlay.myBufInfo[cnt].size;
333 		}
334 		/* this adress is already aligned to the scaler's requirements (via the already modified sizes) */
335 		si->overlay.myBuffer[offset].buffer_dma = (void *) adress;
336 
337 		LOG(4,("Overlay: New buffer: addr $%08x, dma_addr $%08x, color space $%08x\n",
338 			(uint32)((uint8*)si->overlay.myBuffer[offset].buffer),
339 			(uint32)((uint8*)si->overlay.myBuffer[offset].buffer_dma), cs));
340 		LOG(4,("Overlay: New buffer's size is $%08x\n", si->overlay.myBufInfo[offset].size));
341 
342 		/* release the shared benaphore */
343 		RELEASE_BEN(si->overlay.lock)
344 
345 		return &si->overlay.myBuffer[offset];
346 	}
347 	else
348 	/* sorry, no more room for buffers */
349 	{
350 		LOG(4,("Overlay: Sorry, no more space for buffers: aborted\n"));
351 
352 		/* release the shared benaphore */
353 		RELEASE_BEN(si->overlay.lock)
354 
355 		return NULL;
356 	}
357 }
358 
359 status_t RELEASE_OVERLAY_BUFFER(const overlay_buffer *ob)
360 /* Note that the user can delete the buffers in any order desired! */
361 {
362 	int offset = 0;
363 
364 	if (ob != NULL)
365 	{
366 		/* find the buffer */
367 		for (offset = 0; offset < MAXBUFFERS; offset++)
368 		{
369 			if (si->overlay.myBuffer[offset].buffer == ob->buffer) break;
370 		}
371 
372 		if (offset < MAXBUFFERS)
373 		/* delete current buffer */
374 		{
375 			si->overlay.myBuffer[offset].buffer = NULL;
376 			si->overlay.myBuffer[offset].buffer_dma = NULL;
377 
378 			LOG(4,("Overlay: Release_buffer offset = %d, buffer released\n",offset));
379 
380 			return B_OK;
381 		}
382 		else
383 		{
384 			/* this is no buffer of ours! */
385 			LOG(4,("Overlay: Release_overlay_buffer: not ours, aborted!\n"));
386 
387 			return B_ERROR;
388 		}
389 	}
390 	else
391 	/* no buffer specified! */
392 	{
393 		LOG(4,("Overlay: Release_overlay_buffer: no buffer specified, aborted!\n"));
394 
395 		return B_ERROR;
396 	}
397 }
398 
399 status_t GET_OVERLAY_CONSTRAINTS
400 	(const display_mode *dm, const overlay_buffer *ob, overlay_constraints *oc)
401 {
402 	int offset = 0;
403 
404 	LOG(4,("Overlay: Get_overlay_constraints called\n"));
405 
406 	/* check for NULL pointers */
407 	if ((dm == NULL) || (ob == NULL) || (oc == NULL))
408 	{
409 		LOG(4,("Overlay: Get_overlay_constraints: Null pointer(s) detected!\n"));
410 		return B_ERROR;
411 	}
412 
413 	/* find the buffer */
414 	for (offset = 0; offset < MAXBUFFERS; offset++)
415 	{
416 		if (si->overlay.myBuffer[offset].buffer == ob->buffer) break;
417 	}
418 
419 	if (offset < MAXBUFFERS)
420 	{
421 		/* scaler input (values are in pixels) */
422 		oc->view.h_alignment = 0;
423 		oc->view.v_alignment = 0;
424 
425 		switch (ob->space)
426 		{
427 			case B_YCbCr422:
428 					if (si->ps.card_arch < NV10A)
429 					{
430 						/* RIVA128 and TNT need 15.
431 						 * Note: this has to be in sync with the slopspace setup during buffer allocation.. */
432 						oc->view.width_alignment = 15;
433 					}
434 					else
435 					{
436 						/* GeForce need 31.
437 						 * Note: this has to be in sync with the slopspace setup during buffer allocation.. */
438 						oc->view.width_alignment = 31;
439 					}
440 					break;
441 			default:
442 					/* we should not be here, but set the worst-case value just to be safe anyway */
443 					oc->view.width_alignment = 31;
444 					break;
445 		}
446 
447 		oc->view.height_alignment = 0;
448 		oc->view.width.min = 1;
449 		oc->view.height.min = 2; /* two fields */
450 		oc->view.width.max = ob->width;
451 		oc->view.height.max = ob->height;
452 
453 		/* scaler output restrictions */
454 		oc->window.h_alignment = 0;
455 		oc->window.v_alignment = 0;
456 		oc->window.width_alignment = 0;
457 		oc->window.height_alignment = 0;
458 		oc->window.width.min = 2;
459 		/* GeForce cards can output upto and including 2046 pixels in width */
460 		//fixme: how about TNT?
461 		if (dm->virtual_width > 2046)
462 		{
463 			oc->window.width.max = 2046;
464 		}
465 		else
466 		{
467 			oc->window.width.max = dm->virtual_width;
468 		}
469 		oc->window.height.min = 2;
470 		/* GeForce cards can output upto and including 2046 pixels in height */
471 		//fixme: how about TNT?
472 		if (dm->virtual_height > 2046)
473 		{
474 			oc->window.height.max = 2046;
475 		}
476 		else
477 		{
478 			oc->window.height.max = dm->virtual_height;
479 		}
480 
481 		/* GeForce scaling restrictions */
482 		switch (si->ps.card_arch)
483 		{
484 		case NV04A:
485 			/* Riva128-TNT2 series have an old BES engine... */
486 			oc->h_scale.min = 1.0;
487 			oc->v_scale.min = 1.0;
488 			break;
489 		case NV30A:
490 		case NV40A:
491 			/* GeForceFX series and up have a new BES engine... */
492 			oc->h_scale.min = 0.5;
493 			oc->v_scale.min = 0.5;
494 			/* NV31 (confirmed GeForceFX 5600) has NV20A scaling limits!
495 			 * So let it fall through... */
496 			if (si->ps.card_type != NV31) break;
497 		default:
498 			/* the rest in between... */
499 			oc->h_scale.min = 0.125;
500 			oc->v_scale.min = 0.125;
501 			break;
502 		}
503 		/* all cards have a upscaling limit of 8.0 (see official nVidia specsheets) */
504 		oc->h_scale.max = 8.0;
505 		oc->v_scale.max = 8.0;
506 
507 		return B_OK;
508 	}
509 	else
510 	{
511 		/* this is no buffer of ours! */
512 		LOG(4,("Overlay: Get_overlay_constraints: buffer is not ours, aborted!\n"));
513 
514 		return B_ERROR;
515 	}
516 }
517 
518 overlay_token ALLOCATE_OVERLAY(void)
519 {
520 	uint32 tmpToken;
521 	LOG(4,("Overlay: Allocate_overlay called: "));
522 
523 	/* come up with a token */
524 	tmpToken = 0x12345678;
525 
526 	/* acquire the shared benaphore */
527 	AQUIRE_BEN(si->overlay.lock)
528 
529 	/* overlay unit already in use? */
530 	if (si->overlay.myToken == NULL)
531 	/* overlay unit is available */
532 	{
533 		LOG(4,("succesfull\n"));
534 
535 		si->overlay.myToken = &tmpToken;
536 
537 		/* release the shared benaphore */
538 		RELEASE_BEN(si->overlay.lock)
539 
540 		return si->overlay.myToken;
541 	}
542 	else
543 	/* sorry, overlay unit is occupied */
544 	{
545 		LOG(4,("failed: already in use!\n"));
546 
547 		/* release the shared benaphore */
548 		RELEASE_BEN(si->overlay.lock)
549 
550 		return NULL;
551 	}
552 }
553 
554 status_t RELEASE_OVERLAY(overlay_token ot)
555 {
556 	LOG(4,("Overlay: Release_overlay called: "));
557 
558 	/* is this call for real? */
559 	if ((ot == NULL) || (si->overlay.myToken == NULL) || (ot != si->overlay.myToken))
560 	/* nope, abort */
561 	{
562 		LOG(4,("failed, not in use!\n"));
563 
564 		return B_ERROR;
565 	}
566 	else
567 	/* call is for real */
568 	{
569 
570 		nv_release_bes();
571 
572 		LOG(4,("succesfull\n"));
573 
574 		si->overlay.myToken = NULL;
575 		return B_OK;
576 	}
577 }
578 
579 status_t CONFIGURE_OVERLAY
580 	(overlay_token ot, const overlay_buffer *ob, const overlay_window *ow, const overlay_view *ov)
581 {
582 	int offset = 0; /* used for buffer index */
583 
584 	LOG(4,("Overlay: Configure_overlay called: "));
585 
586 	/* Note:
587 	 * When a Workspace switch, screen prefs change, or overlay app shutdown occurs, BeOS will
588 	 * release all overlay buffers. The buffer currently displayed at that moment, may need some
589 	 * 'hardware releasing' in the CONFIGURE_OVERLAY routine. This is why CONFIGURE_OVERLAY gets
590 	 * called one more time then, with a null pointer for overlay_window and overlay_view, while
591 	 * the currently displayed overlay_buffer is given.
592 	 * The G200-G550 do not need to do anything on such an occasion, so we simply return if we
593 	 * get called then. */
594 	if ((ow == NULL) || (ov == NULL))
595 	{
596 		LOG(4,("output properties changed\n"));
597 
598 		return B_OK;
599 	}
600 
601 	/* Note:
602 	 * If during overlay use the screen prefs are changed, or the workspace has changed, it
603 	 * may be that we were not able to re-allocate the requested overlay buffers (or only partly)
604 	 * due to lack of cardRAM. If the app does not respond properly to this, we might end up
605 	 * with a NULL pointer instead of a overlay_buffer to work with here.
606 	 * Of course, we need to abort then to prevent the system from 'going down'.
607 	 * The app will probably crash because it will want to write into this non-existant buffer
608 	 * at some point. */
609 	if (ob == NULL)
610 	{
611 		LOG(4,("no overlay buffer specified\n"));
612 
613 		return B_ERROR;
614 	}
615 
616 	/* is this call done by the app that owns us? */
617 	if ((ot == NULL) || (si->overlay.myToken == NULL) || (ot != si->overlay.myToken))
618 	/* nope, abort */
619 	{
620 		LOG(4,("failed\n"));
621 
622 		return B_ERROR;
623 	}
624 	else
625 	/* call is for real */
626 	{
627 		/* find the buffer's offset */
628 		for (offset = 0; offset < MAXBUFFERS; offset++)
629 		{
630 			if (si->overlay.myBuffer[offset].buffer == ob->buffer) break;
631 		}
632 
633 		if (offset < MAXBUFFERS)
634 		{
635 			LOG(4,("succesfull, switching to buffer %d\n", offset));
636 
637 			/* program overlay hardware */
638 			nv_configure_bes(ob, ow, ov, offset);
639 
640 			return B_OK;
641 		}
642 		else
643 		{
644 			/* this is no buffer of ours! */
645 			LOG(4,("buffer is not ours, aborted!\n"));
646 
647 			return B_ERROR;
648 		}
649 	}
650 }
651