Alpha Shadows > Buffer Lamp???

Okay, I’ve experimented and I’ve searched high and low and I find the same question asked repeatedly with no absolutely, unequivocally definitive answer… so I’ll ask myself…

Is it possible - at all - for an alpha-mapped texture to cast a shadow using buffered spot lamps or is ray tracing essential?

If buffered lamps can’t do it - is it technically feasible (feature request)?

I’m trying to get a soft, semi-opaque tree shadow in a scene using only scanline/buffer renderer. If it can’t be done then I guess I’ll have to use layers or nodes to separate the ray-trace lamp from the rest of the scene or map a shadow texture where I want the shadow to appear?


Noooooo, that’s not the answer I’m looking for. What I need to hear is “Sure you can use buffer lamps, just press the XYZAB button”. Or even “Damn, didn’t we commit that change yet? I’ll get right on to it now - I know it’s here somewhere”

The problem is that I’m trying to build a reasonably complex scene (for me) and the point of the exercise is to exploit buffer lamps all the way and avoid ray tracing completely. I’m figuring it’s the only way I’ll ever really come to grips with buffered shadows.

Oh well, thanks anyway :frowning:

Well where do you think the speed advantage of buffer lamps comes from?
They just do a depth lookup, and the result is either shadow or no shadow. Softening comes through filtering the results of adjacent map entries.

The only solution to this are “deep shadow maps”, they are quite a bit more complex though, definitely not something every other renderer features…
But it has been brought up a few times when irregual shadow buffers has been implemented, so maybe in a few releases…


I thought about modelling it but there’s two problems: 1: It’s a tree shape and 2: The mesh would be opaque and I need it to be transparent.

For now, I’ll compromise by just using a “layer” lamp set to ray shadow for this part.

Hopefully I’ll have something to post in WIP soon enough and then I can get ideas on alternative solutions. I’m finding some very interesting idiosyncrasies with buffer lamps, especially “Shadow Only” spots.


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Actually, I thought the same thing a short while ago. I’ll have to look up the docs. If I can project a negative image, to remove light, that would work well.


Okay, so an image texture on a spot lamp looks promising - except the image seems to project with respect to global co-ords, no matter hwich options I choose. So, if I tilt the textured lamp, the texture stays put - it doesn’t tilt or stretch or anything. If I move the lamp closer/further away, the projected image stays put - it doesn’t change size at all, but the lamp perimeter does.

In other words, it doesn’t work like a projected image, which I’m sure it should but I can’t find much info on it at all. So, if someone can point me toward a recent tute or doc, that would be greatly appreciated.


Typical. Within two minutes of posting I find the answer In a four year old doc. Use the “View” button. I thought I’d tried all three options before, but obviously not.


Sorry RB, I was editing my previous post but apparently forgot to hit “send”. So, I got it to work as expected with “View” in the Texture and Input panel.

Textures seem to have some serious issues in 2.43 (Mac anyway). Loading them is problematic and buggy. I’m going to post my WIP in the WIP forum now so you can see what I’ve been up to.

Thanks for your help so far. I’ll probably have more shadow/lamp questions before I’m finished.