til: fixup til_fb_fragment_t.texture fragmenting

Until now when fragmenting with a texture present the texture
pointer was simply copied through to the new logical fragment.
The problem with that is when sampling pixels from the texture in
a nested frame scenario, the locations didn't align with the
placement of the logical fragment.

With this change when the incoming fragment has a texture, the
output fragment gets some uninitialized memory attached in the
outgoing fragment's texture pointer.  Then the fragmenter is
expected to do the same populating of res_fragment->texture it
already did for res_fragment, just relative to
fragment->texture->{buf,stride,pitch} etc.

It's a bit hairy/janky because til_fb_fragment_t.texture is just
a pointer to another til_fb_fragment_t.  So the ephemeral/logical
fragments fragmenting/tiling produces which tend to just be
sitting on the stack need to get another til_fb_fragment_t
instance somewhere and made available at the ephemeral
til_fb_fragment_t's .texture member.  We don't want to be
allocating and freeing these things constantly, so for now I'm
just ad-hoc stowing the pointer of an adjacent on-stack texture
fragment in the .texture member when the incoming fragment has a
texture.  But this is gross because the rest of the fragment
contents don't get initialized _at_all_, and currently if the
incoming fragment has no texture the res_fragment->texture member
isn't even initialized.  The fragmenters aren't really supposed
to be expecting anything sensible in *res_fragment, but now we're
making use of res_fragment->texture *if* fragment->texture is
set.  This is just gross.

So there's a bunch of asserts sprinkled around to help police
this fragility for now, but if someone writes new fragmenters
there's a good chance this will trip them up.

1 files changed, 10 insertions, 2 deletions

diff --git a/src/til_threads.c b/src/til_threads.c
index e2c8a97..9e55a29 100644
--- a/src/til_threads.c
+++ b/src/til_threads.c
@@ -63,7 +63,11 @@ static void * thread_func(void *_thread)
 			 * which may require a consistent mapping of CPU to fragnum across frames.
 			 */
 			for (;;) {
-				til_fb_fragment_t	frag, *frag_ptr = &frag;
+				til_fb_fragment_t	texture, frag, *frag_ptr = &frag;
+
+				/* XXX: jank alert, need to cleanup texture integration TODO */
+				if ((*(threads->fragment_ptr))->texture)
+					frag.texture = &texture; /* provide space, but the fragmenter must populate it */
 
 				while (!__sync_bool_compare_and_swap(&threads->next_fragment, frag_num, frag_num + 1));
 
@@ -76,7 +80,11 @@ static void * thread_func(void *_thread)
 		} else { /* render *any* available fragment */
 			for (;;) {
 				unsigned		frag_num;
-				til_fb_fragment_t	frag, *frag_ptr = &frag;
+				til_fb_fragment_t	texture, frag, *frag_ptr = &frag;
+
+				/* XXX: jank alert, need to cleanup texture integration TODO */
+				if ((*(threads->fragment_ptr))->texture)
+					frag.texture = &texture; /* provide space, but the fragmenter must populate it */
 
 				frag_num = __sync_fetch_and_add(&threads->next_fragment, 1);