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, 27 insertions, 1 deletions

diff --git a/src/modules/montage/montage.c b/src/modules/montage/montage.c
index eaf8be7..1191a60 100644
--- a/src/modules/montage/montage.c
+++ b/src/modules/montage/montage.c
@@ -120,6 +120,9 @@ static int montage_fragment_tile(const til_fb_fragment_t *fragment, unsigned til
 	unsigned	w = fragment->width / tile_width, h = fragment->height / tile_height;
 	unsigned	x, y, xoff, yoff;
 
+	assert(fragment);
+	assert(res_fragment);
+
 #if 0
 	/* total coverage isn't important in montage, leave blank gaps */
 	/* I'm keeping this here for posterity though and to record a TODO:
@@ -142,8 +145,31 @@ static int montage_fragment_tile(const til_fb_fragment_t *fragment, unsigned til
 	xoff = x * tile_width;
 	yoff = y * tile_height;
 
+	if (fragment->texture) {
+		assert(res_fragment->texture);
+		assert(fragment->frame_width == fragment->texture->frame_width);
+		assert(fragment->frame_height == fragment->texture->frame_height);
+		assert(fragment->width == fragment->texture->width);
+		assert(fragment->height == fragment->texture->height);
+		assert(fragment->x == fragment->texture->x);
+		assert(fragment->y == fragment->texture->y);
+
+		*(res_fragment->texture) = (til_fb_fragment_t){
+					.buf = fragment->texture->buf + (yoff * fragment->texture->pitch) + xoff,
+					.x = 0,								/* fragment is a new frame */
+					.y = 0,								/* fragment is a new frame */
+					.width = MIN(fragment->width - xoff, tile_width),
+					.height = MIN(fragment->height - yoff, tile_height),
+					.frame_width = MIN(fragment->width - xoff, tile_width),		/* fragment is a new frame */
+					.frame_height = MIN(fragment->height - yoff, tile_height),	/* fragment is a new frame */
+					.stride = fragment->texture->stride + (fragment->width - MIN(fragment->width - xoff, tile_width)),
+					.pitch = fragment->texture->pitch,
+					.cleared = fragment->texture->cleared,
+				};
+	}
+
 	*res_fragment = (til_fb_fragment_t){
-				.texture = fragment->texture,
+				.texture = fragment->texture ? res_fragment->texture : NULL,
 				.buf = fragment->buf + (yoff * fragment->pitch) + xoff,
 				.x = 0,								/* fragment is a new frame */
 				.y = 0,								/* fragment is a new frame */