first off, credit should go again to ydnar and rgoer for developing the excellent alphamod volume brushes, which without, our mapping would be a lot slower and more painful.
the blending will work in any q3 engine game that uses ydnar`s q3map2, although we need at least version 2.5.14
edit: updated shaders as recommended by ydnar to use q3map_baseshaders
image 257 shows a piece of hand built ground with shallow bumps, although for this type of blending it could be totally flat and or have steep angles like a rock face, ie the angles aren`t very important.
the trisouped brushes are painted with caulk on all but the top faces, where a simple lightmapped grass shader is used, but almost any shader or plain tex could be used on the top face.
also note the shapes of the tris brushes aren`t all the same in my example, so neatly aligned grids of trisouping are no longer needed, like with the old indexmap and meta shader terrain blending.
textures/_ratty_terrain/grass
{
qer_editorimage textures/_ratty_terrain/green_terrain.tga
q3map_lightmapsampleoffset 16
q3map_lightmapmergable
q3map_shadeangle 178
q3map_tcmod rotate 33
q3map_nonplanar
q3map_forcemeta
q3map_tcgen ivector ( 512 0 0 ) ( 0 512 0 )
surfaceparm grasssteps
{
map textures/stone/mxrock0b.tga
}
{
map $lightmap
blendfunc filter
}
}
image 258 shows two smaller areas I`ve selected and painted with a dirt shader, again almost any shader or plain tex could be used for those.
textures/_ratty_terrain/base6
{
q3map_lightmapsampleoffset 16
q3map_shadeangle 178
q3map_nonplanar
q3map_forcemeta
}
textures/_ratty_terrain/dirt
{
qer_editorimage textures/_ratty_terrain/brown_terrain.tga
q3map_baseshader textures/_ratty_terrain/base6
q3map_tcmod rotate 33
q3map_tcgen ivector ( 256 0 0 ) ( 0 256 0 )
surfaceparm grasssteps
{
map textures/_ratty_terrain/ratty_dirt_m03.tga // dirt
//rgbgen const ( 0.6 0 0 ) // uncomment to debug
}
{
map $lightmap
blendfunc filter
}
}
image 259 shows one of the dirt areas cloned and “regioned” off, ie all other brushes are hidden from view.
the clones are then grouped and painted with a nodraw shader on all but their top faces, where the blend shader is painted… the func_group doesnt need any additional keys added to it, just its classname.
around the outside, but still part of the group, are the alphamod volume brushes which can be any size and shape, as long as they enclose the specific verts, from the other grouped brushes that we want faded… the shader for them is below the nodraw and blend shaders.
textures/_ratty_water/nodraw_nonsolid_trans
{
qer_editorimage textures/_ratty_terrain/nodraw_water.tga
qer_trans 0.5
surfaceparm nonsolid
surfaceparm nodraw
surfaceparm trans
}
textures/_ratty_terrain/base1
{
q3map_shadeangle 178
q3map_tcmod rotate -66
q3map_nonplanar
q3map_forcemeta
q3map_nolightmap
surfaceparm nonsolid
surfaceparm nomarks
surfaceparm trans
}
textures/_ratty_terrain/dirt_volume_blend
{
qer_editorimage textures/_ratty_terrain/red_grey_terrain.tga
q3map_baseshader textures/_ratty_terrain/base1
q3map_tcgen ivector ( 256 0 0 ) ( 0 256 0 )
//cull disable // uncomment to debug
polygonoffset
{
map textures/_ratty_terrain/ratty_dirt_m03.tga // dirt
rgbgen vertex
//rgbgen const ( 0.5 0 0 ) // uncomment to debug
alphagen oneminusvertex // inverses the value of the volume alpha
alphafunc ge128
}
}
textures/_ratty_water/alpha_0
{
qer_editorimage textures/_ratty_terrain/alpha_0.tga
qer_trans 0.75
q3map_alphamod volume
q3map_alphamod scale 0
surfaceparm nonsolid
surfaceparm nodraw
surfaceparm trans
}
image 262 shows the original rtcw dirt tex and the alpha channel I made for it, note the gamma is quite high although there is still some contrast.
image 263 is a shot of psp7, and the right side image shows where I layered in some slightly darker staining, around the middle of what will become the alpha channel, using psp`s multiply blending.
although the staining could be around the border where the tex would tile in game, which is how I set up some of my rock tex alpha channels.
Im assuming photoshop would have similar ways of blending layers? ...and possibly easier to use, but I like psp7 partly as its cheap but also because I like it`s interface.
anyway… the left side image shows the gamma altered, grayscale version of the original dirt tex before the staining was layered in.
I also found the more speckled the layers are, the better the eventual blend results will be, as these types of tex filtering then help the map`s vertex alpha and shaders alphafunc, determine where to break up the tiled blend tex in game.
ie the resulting blending is more dithered and natural looking, then a smooth linear gradient would produce which is what the old terrain. meta shaders used.
if your making your own tex and or alpha channel, almost any alpha channel would work, providing its gamma is high enough, so dont be put off if any of you aren`t familiar with a paint program.
back to the map…
image 260 shows both the dirt areas which can be grouped into one func_group.
the important thing here is I cloned some more of the original grass brushes, around the outer edge of the volume brushes, and added them to the group, then painted them to use the same nodraw and blend shaders as above.
note, I also deleted any brushes that dont have at least one vert enclosed by a volume brush, as they wont be visible in game, so are redundant and probably would add to the over draw if left in as I`m assuming they would still need to be culled by the alphafunc, thus wasting fps.
if the blend area was larger or it`s trisouping was made of smaller brushes, then most of the middle of the group could be deleted.
it also doesn`t matter if two or more blend areas are touching each other, as long as there are at least two tris brushes, separating any volume brushes from different areas… other wise the volume brushes cancel each other out, and the blending would result in more of a visibly “joined” area, rather then two or more “separate” but nearby areas of dirt.
image 261 shows the selected groups overlapping the original grass brushes and the simple non blended dirt brushes, in the middle of the blending brushes.
hopefully it should be more obvious what were doing here, but in case its not, here`s roughly how it works.
the non blended dirt brushes are drawn as normal in game with little or no overdraw, so are the grass brushes.
the alphamod volume brushes produce a solid, 100% opaque border, which the polygon offset, decal type blending, fades towards from it`s 100% translucent edges, which are dithered looking like the dotproduct terrain blending.
this covers up the noticeable seems between the dirt and the grass brushes, although it does produce some overdraw, but as I only use alphafunc ge128, and not the slower but more precise blendfunc blend, then this is still quicker then most multi layered dotproduct shaders take to draw, and a more flexible system to work with, as we can control almost exactly where we want the blending to be.
note, the blended brushes could use a different color channel instead of dirt… eg sand, so it could be dirt areas blending into sand, blending into grass.
k, that may look a little odd as the sand would appear to surround the dirt areas in this example, although we dont have to have closed areas, so they could be borders between fields, or a winding dirt path with grass on either side... technically the principle would be the exactly same, and Im sure some of you will find creative uses for this 
image 264 is a high up, in game shot with r_showtris 1, looking down on the dirt areas with no blending.
an rgbgen const ( 0.6 0 0 ) is used to color the dirt red for debugging purposes… ie this makes it much easier to see where there are hard edged borders between the dirt and grass.
the values are normalized rgb, ie between 0.0 and 1.0
image 265 shows the same scene but now with the dirt blending, again colored red, clearly showing a dithered dot product type edge… notice how it “bleeds” over the white tris lines.
side note, I found the best dotproduct results are when the angles of the tris are tweaked vertically, so any dotproduct blends don`t lie sharply along tris edges, ie we want them bleeding over instead of cut off.
image 238 shows an example of this, which I`ll cover in more detail in another tutorial.
image 266 shows just the blending colored red with no showtris.
I often use the cull disable lines in my shaders, when debugging so I can view in game the blending from underneath, this is especially useful when doing dot product or volume blending on rock or mountain faces, which I`ll be covering in my next tutorial …as well as showing a couple of methods to reduce the amount of tex tiling patterns, using volume blending and alpha channeled decals.
although the latter method is mostly redundant now, but some mappers might still find it useful to know.
image 267 shows the final blending result in game with the camera at normal player head height, although I also took the shot with cg_drawgun 0.
imo, this is worth mentioning as sometimes the apparent camera height or scale of the tex and or brush work can be deceptive, especially if there are no man made buildings or models like trees to use as scale ref.
more relevant in this case, note the non blended dirt in the lower left of the pic is slightly darker then the blended dirt, although I quite like this result.
but if it was too obvious then I would use the q3map_vertexscale to lower the gamma of the blend tex, which remember is rgbgen vertex lit, as opposed to lightmapped lit.
this is to save on fps, and because it`s difficult to blend the lightmap stages, but some mappers will probably pref to use all lightmap shaders where possible.
and lastly for now… I`m sure most of you will agree, the blending between the dirt and grass is very natural looking, even more so then the old linear blends of terrain meta shaders :drink:
