I had another idea to just test the alpha values for 50% alpha and then skip writing to the frame buffer and that didn't work either (framebuffer is full of false pixels anyway). Instead of banging my head into the wall I just steped back and thought about needing this feature at all and no, there is no need for that in this game: I can just delete or don't use anything with multiple alpha layers. For example the palm had 3 layers of palm leaves, but I killed 2 of them and no everything is working perfectly (I still have to sort objects and to render first solid, then alpha materials, but thats pretty fast). I'm happy I got this solved :-)

The Editor was also improved a bit and everything needed for a full mission can be set there. As you can see on the screenshot there are a couple of new features for the map: Roads, some more neutral objects and some enemy units. Shadows and shaders would be nice too, but there is no time for that right now. Maybe I will be able to put that into the engine next week.

Moving around with the tank and aim and shoot on stuff should work tomorrow. Effects and AI won't be complete till christmas, there will be most likely only a couple of standard effects. Also collision detection is another big issue.