If you place an object in front of another object, activate transparency with raytracing for the front object and put a image/movie texture on the background object with 'screen' mapping selected for the background object, any part of the background object behind the transparent object shows light gray. You cannot see through the transparent object.
I have tested with flat planes, 3D objects with and without a subdivision surface modifier – the bug is very easy to reproduce and shows up on Windows and Ubuntu Linux.
I have attached a simple blend file with a transparent cube (raytrace selected) in front of two planes with an image texture. The plane on the right has Generated coordinates and works fine, the one on the left uses screen coordinates and when rendered shows gray behind the cube.
The Blender build number is: 2.26.0 r34161
Tested on AMD Phenom II X4 940 with a ATI 2400 HD graphics card and 3 GiB RAM.
WinXP and Ubuntu Linux 10.10.
Description
Description
Event Timeline
Raytracing has no information about screen space, which makes this option fail. The screen mapping feature was added like 12 years ago, and hasn't changed much... a reason why it doesn't support easily newer features we've added. I'll make a note on this case for when we'll refresh our internal shader system for 2.6
As you can see, we've got some work ahead:
http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Tools#Rendering