rasterizer & transparency & framebuffer

[pinkplum]

Hi there,

I'm trying to write a shader that use transparency with rasterizer and put each passes into user framebuffer. For some reasons, I found that the output for each pass doesn't look right.

Can anyone shed some light on this?

I tried 'rast useopacity' but still doesn't work.

[haggi]

If you render with rasterizer, the alpha value is used as transparency value. e.g. I wrote a hair shader where I simply forgot to set the alpha value of the *result. So it was still 0 and in rasterizer I could not see anyting where in scanline everything worked fine.

So you can either set the alpha value to a desired number or you can set the opacity explicitly with mi_opacity_set() if it differs from your alpha.

[pinkplum]

thanks for the answer haggi.

I've already set the alpha value, and also tried the mi_opacity_set.
I'm writing hair shader as well and I tried to do the tip fade by setting alpha to 1 at root and interpolate to 0 at tip.

I tried my shader with one single hair, I can see the result with the opacity but it doesn't look right to me.

It has the opacity but it doesn't seem to be 1 at root and 0 at tip after all. but when I wrote out the same output to framebuffer the result in framebuffer came out as I expected.

But the problem is I like the look of the result that doesn't look right and I don't know how it got that way.

[Puppet]

Please show you result images.
You may view source code from another hair shaders (for example p_HairTK) how it works with rasterizer.

[Puppet]

In theory code scheme should be like this:

if(transparency && state->options->scanline != 'r')
{
	mi_trace_transparent(&trans_color, state);
	result = inv_alpha * trans_color;
}

result += color * diffuse * alpha;

if(state->options->scanline != 'r')
	color_pass = color * alpha;

mi_fb_get(state, color_pass_buf, get_color_pass);
color_pass = get_color_pass * inv_alpha + color_pass;
mi_fb_put(state, color_pass_buf, &color_pass);

Ups, sorry, it was old post

[RGhost77]

In theory code scheme should be like this:
Ups, sorry, it was old post

Anyway, in 3ds max 2011 and 2012 rasterizer calculates wrong transparency. (mr sa 3.8 working well, it seems this is max's bug)

[bart]

So please specify what versions we are talking about here.
There are controls per-framebuffer which could possiblyl affect the calculations.

Also, if you are going to be using mi_fb_get, your shader network layout and calling order may matter. Ie, you'd probably want to make sure that there is a valid value representing the object layer behind the transparency.