I have recently completed a fire tutorial found in the Blender Art Magazine issue 16, Burn Them All. I have two questions the first is that it will on render about the first thirty frames. I also tried the demo file that came with the magazine and it did the same thing only it didn’t even do 30. The other question I had is that is there a way to render just the fire with an alpha background and then combine that with a regular render or movie. I think that I could do this but it won’t render the background as alpha. Or is there a way that the node composition or whatever it is called will affect only the fire and not the surrounding things.
I’'m new to Blender and I have just been working through that same tutorial. I think I can help with your first question. The problem is that the animated sphere you create on page 40 shrinks to size 0 at frame 30. I don’t know why the tutorial says to do this because it makes all the spheres disappear in the render. I set it to a little greater than 0 and I can render all the way to frame 250.
I have another question. I could not get the lattice deform to work with particles flowing from the monkey head and had to switch to a plane for my emitter. When I tried with the monkey the particles would start being emitted in empty space above the head (I used the lattice vertex group just like the tutorial said so as to not deform the monkey mesh). Did you get that to work?
I also found I had to do the following
Page 40 - do a set smooth on the sphere
Page 40 - turn the shadow option off in the shaders panel for the sphere
I’ve now been looking at your second question and I think I’ve figured it out. The trick is to use layers and Render Layers (two different but related concepts) and the node editor. The chapters of the manual on layers and Render Layers will explain all this better than I can.
Here is an outline of the steps, the manual will help fill in the details.
Place your fire on one layer (e.g layer 1) and other objects on another layer (e.g layer 2). Make
sure you make your lamp and camera shared objects between the two layers so that the second layer has light etc (using M and shift clicking the layer buttons the appear in Object mode).
Bring up the Render buttons and look at the Render Layers panel
Set the default Render Layer 1 to contain only the first layer with the fire (by clicking the buttons in the bottom set of 20)
Create a new Render Layer (2) and set this to contain only the second layer (again using those bottom buttons).
Now using the top set of 20 buttons use shift+click to make sure both layers are selected for rendering.
Bring up the node editor. Add new->Input->Render Layer and set it to Render Layer 2 (the new one you created.)
Create an Add->Color->Mix node at the end of your fire node chain.
Plug the end result of the fire node chain into one image input of the new add node.
Plug the image from the Render Layer 2 node into the other image input of the add node.
Use add or mix modes and adjust the fac
Plug the output into composite and viewer output nodes
Actually I was a little wrong in my previous post. As well as the layers and render layers you also need to use the green screen technique on one layer and add matte nodes to that render layer in the node editor. With this you can make the background transparent and combine the images so that the
fire composite noodle does not effect the other layer and both combine properly.
I’ve been working further on this. I’m new so can’t post any links as yet but I was a little incorrect above. As well as Render Layers you need to put the transparency back into your fire noodle. I found I could do this by taking the image output and linking it to a map value node. The output of the map value node then goes to a set alpha node which takes as it’s other input the fire image. You now have the fire with transparency to mix (e.g using alpha over) with other background objects.
