On Monday 09 January 2012 10:31:24 Stuart Buchanan wrote:
> On Mon, Jan 9, 2012 at 10:00 AM, <thorsten.i.renk wrote:
> >> I don't think the Model matrix will help you much either, as IIRC
> >> (0,0,0) is the center of the earth spheroid.
> >
> > Hm, the line is
> >
> > gl_Position = gl_ModelViewProjectionMatrix * gl_Position;
> >
> > Doesn't gl_ModelViewProjectionMatrix transform things into 2d screen
> > coordinates?
>
> Correct (hence my reference to the Model matrix, rather than
> ModelViewProjection matrix).
>
> > Would it work if I use a different matrix instead? Apparently
> >
> > vec4 groundPoint = gl_ModelViewMatrix * vec4(0.0, 0.0, 0.0, 1.0);
> >
> > can be used to generate the zero altitude point just below the current
> > view, so then the length of the difference vector dotted with an 'up'
> > normal would represent altitude (?)
>
> I didn't know that.
>
> >> What do you need it for? sunrise/sunset lighting?
> >
> > Yes, the earthShade factor should affect objects dependent on their
> > altitude, basically I want glowing high-altitude clouds whereas the
> > lower
> > clouds are still dark.
>
> Thought so. That would be yet another nice effect to add :)
>
> On Mon, Jan 9, 2012 at 10:08 AM, Emilian Huminiuc wrote:
> > In the transition shader (and the other terrain shaders), using
> > gl_Vertex.z works as a good aproximation (it's used to determine if
> > there should be snow painted, sometimes it behaves funny, but it's
> > generally reliable enough), but for clouds maybe using the final value
> > of gl_Position.z might give you what you want?
>
> The gl_Vertex of the terrain has a different coordinate system
> (presumably based on
> (0,0,0) being the center of the tile at sealevel?) than the clouds
> (where (0,0,0) is the
> center of the sprite).
>
> -Stuart
>
I know that, that's why I suggested the final position, which should be
actually given by ecPosition.z. (At least for fogging the trees that works as
expected, I assume the trees use roughly the same approach).
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