**System Information**
Intel Core i7, 8 Gb RAM, AMD Radeon HD 7700
Windows 7 x64
**Blender Version**
Broken: 2.76, 2.77
Worked: no information
**Short description of error**
When all materials on scene are using Nodes, it isn't possible to use node-based alpha maps. This case is quite confusing so I've created a test file to explain it:
1. Open the attached file {F314462}and switch from Material to Rendered shading mode. You will see that alpha mapping doesn't work. If you'll move the Alpha slider in material Transparency option you will see that alpha itself actually does work, but it doesn't respect any kind of map attached to it.
2. Select the bottom plane and you will notice that Receive Transparent option is turned on. Now disable Use Nodes option and alpha mask will work.
**Exact steps for others to reproduce the error**
Here is an approximate way to reproduce the whole thing:
1. Create two planes, one above the other. There should be a default Sun lamp with Ray Shadow turned on, if your scene doesn't have one, create it as well.
2. Apply material to the bottom plane, turn on Receive Transparent option.
3. Apply material to the top plane, turn on Transparency, turn on Use Nodes and reattach its material where needed. At this point we still have two opaque materials.
4. Create some kind of black and white mask: it could be a vertex paint or a black and white image.
5. Apply the mask by connecting it to the Alpha channel of the Output Node or create Extended Material and attach the mask into its Alpha input and then connect Material and Output alphas. At this point you should see the effect of the mask in Material Shading mode.
6. Render your scene or just switch the viewport Shading mode to Rendered and you will see that black and white map work as expected and drops transparent shadow on a bottom plane.
7. Now select the bottom plane, turn on Use Nodes in its material and reattach its material where needed. At this point you will see that Receive Transparent option doesn't work anymore despite the fact that it is still turned on.
The key point here seems to be that it isn't possible to use alpha maps by attaching them into Alpha slots when another material is using nodes as well. It is still possible to attach the same map directly inside material via texture slots and it will work as expected, but it won't be possible to attach vertex colors that way and there won't be any way to use node mixing capabilities so this can become a real problem for those who is still using Blender Render. Yes, it isn't as popular as Cycles, but it's still a part of Blender and it is still quite useful for simple tasks.
{F314462}