You don’t need yafray for this because caustics aren’t involved with projectors due to there being no refraction in the slide. The way I see it, you can do it 3 ways:
- make a mesh for the slide and screen and a spotlight.
- map an image onto the slide and set raytransp on. Set fresnel between 1 and 3 and factor between 1 and 1.5.
- select the screen (projected mesh) and set it’s material with trashad on so it receives the transparent shadows.
This way is slow because it uses ray shadows. It can cause artifacts on the projection. It’s also difficult to adjust the projected image (especially brightness).
Just put the image directly onto the screen. This can be done via UVs or just resizing the texture in the map to section. This would mean that if you move the projector, you have to adjust the UVs every time. For that reason alone I don’t recommend it.
Map the image onto the light. At the right of the spotlight panel, add the image as a texture, make the coordinates use view instead of global. Now, this mapping squares out your image so you have to adjust the size to fit the aspect ratio of your image.
This method tiles your image though (does anyone know how to turn off tiling?), and it also seems to warp the edges (I guess because it’s mapped to a light that projects spherically - so you might have to warp your images to counter this). The good thing about this method is you don’t have to move the images if you want to move the projector.
However, I don’t know if you plan on animating the slides changing. If so, method 3 gets a bit tricky. You could maybe get away with animating the textures but I don’t know how you do this or if you can with lights.
Here are pictures of methods 1 and 3. I reckon method 1 might be best for it being easy and accurate. But you’d have to figure out how to make the projected image brighter. It can possibly be done by adding a texture to the screen and using some effect to darken the colours. BTW, in the first image, the white dots are the artifacts caused by method 1. The second image is a bit squished as I forgot to change the aspect ratio but you can see it’s clearer. I used a halo spotlight so you can see where it is.
Because I’m using geocities, you have to click the link and when you see the page fail, hit return in the location bar. Either that or copy/paste the urls: