I've created an overlay with an alpha channel (a tga file) and used Nems' Tools VTF editor to create the texture with a transparent background. However, the overlay only works when applied to walls.

When I'm in Hammer, I can add overlays to both walls and floors/ceilings and, initially, they appear to show up correctly. However, when I run the map only the overlays on the walls show up in Portal. Also, if I save the map, close hammer, and re-open the map in Hammer, then the overlays only show on the walls but not on the floors or ceilings.

Anybody know what's going on?

Have you checked if those ceilings/floors are func_brushes or world brushes? func_brushes don't accept overlays.

The other possibility is that the material you are using for ceilings and floors contain the parameter "$nodecal" "1". What textures are you using there?

Thanks, josepezdj. I've had another play and I've sussed it.

The brushes were all world brushes but the ones on the floor and ceiling had previously been cut using the clipping tool. I deleted the brushes and redrew new ones and the overlays now work OK. Looks like using the clipping tool can have some undesirable effects.

Did you clip before or after applying the overlays? The clipping tool causes the brush faces property of overlays to be cleared. You might want to try choosing the "Brush Face" property, select the picker button and then click all the brushes it needs to apply to.

I had clipped before applying the overlay.

I realize that clipping affects existing overlays and in the past I have had to re-apply overlays when the brush they were on had been clipped - but this is the first time I've come across an example where the resultant brush refuses to accept an overlay (and that includes both my custom overlay as well as built in overlays.

albian wrote:
Looks like using the clipping tool can have some undesirable effects.

It's not about an undesirable effect, it's the way things work :p Every info_overlay entity needs a brush face number to be applied to. Each new brush that you create into Hammer gets automatically a set of 6 numbers, one per brush face. When you use the clipping tool, you are actually creating new brushes by dividing one already existing brush in more brushes: all of them get automatically a new brush face numbers...

Do as TeamSpen suggested to avoid re-creating the overlays: open it's properties, go to "Brush faces" and use the picker tool to select the brush side/s you'll want it to be applied to, and you're done

OK, so I'm still getting problems with overlays not showing up on some brushes and have concluded that it's not the clipping tool to blame. To be honest, it could possibly be some kind of compiler bug. I'm working with a large map (see stats below) and am occasionally finding brushes that don't accept overlays. The overlays appear to be there in the editor when first added but don't appear when the map is compiled - and also, if I close the map and re-open it, then they don't appear in the editor (just the little overlay icon is displayed).

I just tried a test where I had one brush where the overlay wasn't being display. I deleted everything in the map except for this brush and the overlay, surrounded it with a hollowed out cube, and then compiled it - with this very simply map, the overlay was displayed correctly. SO I still can't work out why it wasn't being display in my original map.

Stats for my map:
Object names Objects/Maxobjs Memory / Maxmem Fullness
------------ --------------- --------------- --------
models 414/1024 19872/49152 (40.4%)
brushes 4410/8192 52920/98304 (53.8%)
brushsides 33686/65536 269488/524288 (51.4%)
planes 23360/65536 467200/1310720 (35.6%)
vertexes 20945/65536 251340/786432 (32.0%)
nodes 8597/65536 275104/2097152 (13.1%)
texinfos 2512/12288 180864/884736 (20.4%)
texdata 256/2048 8192/65536 (12.5%)
dispinfos 0/0 0/0 ( 0.0%)
disp_verts 0/0 0/0 ( 0.0%)
disp_tris 0/0 0/0 ( 0.0%)
disp_multiblend 0/0 0/0 ( 0.0%)
disp_lmsamples 0/0 0/0 ( 0.0%)
faces 12039/65536 674184/3670016 (18.4%)
hdr faces 0/65536 0/3670016 ( 0.0%)
origfaces 8126/65536 455056/3670016 (12.4%)
facebrushes 2964/0 5928/0 ( 0.0%)
facebrushlists 12039/0 48156/0 ( 0.0%)
leaves 9012/65536 288384/2097152 (13.8%)
leaffaces 13941/65536 27882/131072 (21.3%)
leafbrushes 10115/65536 20230/131072 (15.4%)
areas 19/256 152/2048 ( 7.4%)
surfedges 86858/512000 347432/2048000 (17.0%)
edges 50779/256000 203116/1024000 (19.8%)
LDR worldlights 743/8192 74300/819200 ( 9.1%)
HDR worldlights 0/8192 0/819200 ( 0.0%)
leafwaterdata 6/32768 72/393216 ( 0.0%)
waterstrips 883/32768 8830/327680 ( 2.7%)
waterverts 0/65536 0/786432 ( 0.0%)
waterindices 14316/65536 28632/131072 (21.8%)
cubemapsamples 7/1024 112/16384 ( 0.7%)
overlays 151/512 53152/180224 (29.5%)
LDR lightdata [variable] 15196052/0 ( 0.0%)
HDR lightdata [variable] 0/0 ( 0.0%)
visdata [variable] 487644/16777216 ( 2.9%)
entdata [variable] 534113/393216 (135.8%) VERY FULL!
LDR ambient table 9012/65536 36048/262144 (13.8%)
HDR ambient table 9012/65536 36048/262144 (13.8%)
LDR leaf ambient 29989/65536 839692/1835008 (45.8%)
HDR leaf ambient 9012/65536 252336/1835008 (13.8%)
occluders 0/0 0/0 ( 0.0%)
occluder polygons 0/0 0/0 ( 0.0%)
occluder vert ind 0/0 0/0 ( 0.0%)
detail props [variable] 1/12 ( 8.3%)
static props [variable] 1/113702 ( 0.0%)
pakfile [variable] 623135/0 ( 0.0%)
physics [variable] 1629327/4194304 (38.8%)
physics terrain [variable] 2/1048576 ( 0.0%)