I've just found that the mtl_specBump which comes with 3DGS supports a specular map in the texture alpha channel, so it uses a specular map if you add an alpha channel to the texture

that's a once-color gloss map as lostclimate said. Real specmaps are colored.(the one on the wiki supports that, lostclimate's shader.)

Don't want to be nitpicking, but I think that's wrong.

A gloss map affects the "power" parameter in specular equation. This parameter tells how sharp the highlights are, something very glossy makes sharp highlights and something not glossy makes wide diffuse highlights.

A specular map is something different, it determines the brightness of the highlights. It can be monochrome or colored but its still a specular map.

Gamestudio shaders support specular maps, not gloss maps.

And the shader on the Wiki, if you mean the "Old Normalmapping with specular map", I would not recommend it, it's multi-pass and much slower than the gamestudio shaders. If you really need different colors for a specular map its better to modify the gamestudio shader.

@losticmate :
Just go to User ressources, to find the model and download link
it works well with normal map only and the standard library shader mlt_Bump from A8.
It's reaaly strange A8 don't have the real normal map/specular map on it's library !

Specularity is just a reflection of light, but no real reflection, it is some fake. So you see a light spot on your surface, wandering in realtime angled to the light source. The size of this light spot can be controlled by the glossiness value. The brightness / strength of this value can be controlled by a spec value. For realistic materials it is better to use a texture to control the specularity. High reflective parts like ice or metal are brighter, almost white and surfaces with low or no reflection are darker (textiles, wood).

Color is not really needed. Black and white can encode the strength of light reflection. If you need to simulate a red light, that reflects on your surface, then it is better to just change the spec light as one RGB value in the shader or as a parameter of this shader. With this in mind the alpha-channel indeed can store the spec map, while another parameter can control the spec color and yet another for the glossiness.

And actually this is how all these engines work when you look into their material editors. You see slots for diffuse and normal. Sometimes you have to add a spec map, sometimes it has to be stored in the alpha channel of the diffuse map. And then there is a slider for glossiness and a color-dialog for the spec color.

And when you want to simulate it really realistic, then you can change the spec color during the game, fitting to the next light color. Maybe even a little transition zone has to be built. But often this makes only a minor difference so most materials just use white spec color.

Well i'm ok Machinery_Frank !

But for a model having clothes parts, metal parts of armor , all in one texture, specularity is important and makes the difference, depending on your level lightening and type of game !
If you have far view for RPG action , yes simple specular color would do the work !
If you make the model with attached sperated parts, a simple full specular on metal parts can be ok !
it really depends on the model type, if it's a big driven
car, specular on scratches with a specular map could make the difference !

I think it can be tried also to view what can be the possible good solutions.

I really hope A8 to have that type of shader and why not , a panel to choose the shader and normal map, spec map on slots !
for shader with

I guess you did not understand. When you copy a specular map into the alpha channel of the diffuse map, then you have all the featues you mentioned. It is the same spec texture with the only limitation that it is made from grey tones instead of color.

In fact, specular maps are generally variations of grey,
for color you have the diffuse map
Even if i know some made shaders taking account of color
for the specular part.
For my use , grey variations are already complete i don't need
color information for specular, so yes, a shader with a specular
on alpha instead of separate texture would suffice.

and that shader would be the default gamestudio shaders?

the default mtl_specBump shader supports a gery-scale specular map in the alpha channel of the texture.