For beta9+ :

Meters are now composited as follows (most things are optional, new stuff disables old images):


1) meter_bg_mcp meter_bg_tcp meter_bg_mcp_master
These can have pink lines to control stretching, yellow lines to allow extents outside of the actual meter.
If they have alpha channel it is blended (inside the meter) against the VU background color (interlacing color) from the theme; outside the meter it blends with the tcp/mcp background etc.

2) meter_bg_v meter_bg_h
These can have pink lines to control stretching, and alpha channel

3) meter_strip_v meter_strip_h meter_strip_v_rms
No pink/yellow line support.
Can have alpha, but CAUTION in this, especially relating to differences l/r on meter_strip_v, etc, as the scaling
may make the alpha useless. Using a constant alpha value might be a nice way to go.

These are each 8 slices (left to right for meter_strip_v, top to bottom for meter_strip_h):
  1) unlit
  2) lit
  3) unlit (clipped channel)
  4) lit (clipped channel)
  5) unlit (record armed)
  6) lit (record armed)
  7) unlit (clipped channel) (record armed)
  8) lit (clipped channel) (record armed)

4) meter_clip_h meter_clip_v
Can have pink lines, alpha. Scaled across the entire clip area. 
 
Two slices (left to right for meter_clip_h, top to bottom for meter_clip_v -- note that this is opposite of the strips)
  1) unlit
  2) lit

4a) meter_clip_v_rms meter_clip_v_rms2
Similar to #4, except RMS clip (and RMS-good area for meter_clip_v_rms2). Pink lines and alpha OK.

5) meter_ol_v meter_ol_h
Can have pink lines to control stretching, and alpha channel (Which you would always want to use!). Drawn over
the same rect as meter_bg_h/v

6) meter_ol_mcp meter_ol_tcp meter_ol_mcp_master
Pink lines supported, must use alpha. Same rect as meter_bg_mcp/etc (outside of meter area, over most controls). 
If you want a nice shine that extends out, you'd use this.

7) meter_mute meter_automute meter_unsolo meter_solodim meter_foldermute
Drawn, if present, instead of the text that labels these things at the top/right of the meter. Scaled to fit (and 
preserve aspect, at least somewhat stupidly), but can support pinkline etc too, though I think the aspect ratio
calculation might get confused by the pinkness. Probably want to use alpha channelage too.

Other notes:

If meter_strip_v is set, then the old mcp_vu image is ignored, etc
mcp_master images often fallback to the mcp version if necessary

Layouts can use image subdirectories for meters, too.

WALTER:
  set tcp.meter.vu.div [2] 
   ; to set division between channels (it may be reduced if necessary to fit the channels,
   ; but only as a last resort
      second field describes spacing logic:
         = 0 for new default, put all space in middle if possible
         = 1 for center, increasing middle by 1px max
         = -1 for all even division/sizes
         = -2 for uneven sized elements

   
      master.mcp.meter.vu.rmsdiv -- 
          first value = division between RMS and normal channels 
          second value = adjust RMS area size in rms+peak mode 
      master.mcp.meter.rmsreadout.color (color of rms readout on master)
      *.meter.readout.color (two color pairs with alpha, for normal and clipped states)
      *.meter.scale.color.unlit.top -- two colors (fg and shadow)
      *.meter.scale.color.unlit.bottom -- two colors (fg and shadow)
      *.meter.scale.color.lit.top -- two colors (fg and shadow)
      *.meter.scale.color.lit.bottom -- two colors (fg and shadow)

      *.meter.inputlabel.color -- one color (text label for recarmed input)
      *.meter.inputlabelbox.color -- two colors (bg and fg) of recarmed input box (with alpha)