How to make an alpha texture for a simple particle

Game Engine Game Engine Support and Discussion
1

Hi all,

I am trying to follow an old tutorial on how to make a particle emitter. I get most of the tutorial (for 2.49) but I get stuck when trying to make a simple particle with transparent background from a plane.

So, how do you do this? I have tried to find tutorials, but most are with 2.49b and are useless as the layout and button grouping has changed. If someone can run through the steps or point to an updated tutorial I would be grateful.

Many thanks

Paul

2

Particles aside, we often want to map a partially transparent image to an object, often a plane. Is that what you are asking? How to create an image in Gimp or whatever that has areas of total and/or partial transparency?

3

Sorry I didnt make myself clear:

I can make an emitter to add objects (the polygon planes) via logic blocks.

What I need to know is how to map a simple .png onto a plane that has alpha transparency. The .png itself is a simple black and white texture.

4

Ok, so the png has transparency? If you loaded it into Gimp you’d be able to see some grey and white squares through parts of the image? Ok. Blender might be able to make black transparent but I’ve always prepared transparency in Gimp (apart from fontsheets and I did that once about a year ago). So what follows should work for images that already have transparency.

I’m not running blender atm so I might make a slip. Bung down a plane and give it a material. Go down to Z transparency and check the box and wind the slider down to 0. Go to Properties > Mesh and click the + to add UV texture. Don’t worry about naming it. While you are there you might as well check a box making it two sided. Go to Properties > Texture and select “Image or Movie” and a little beneath that you can load the image file. Beneath that, Mapping it might be, there’s a button labelled Generated. Click that and select UV. Further down theres a vertical column of check boxes. Check one labelled Alpha. And by now you might see your image on the plane. If not put the mouse into the 3d view and wheel it to refresh the display. If that doesn’t work, I’ve made a slip or haven’t been able to point out the landmarks well enough.

5

Equip’s right - that’s basically everything that you need to know. If you have just a white and black image, you can also use the Add blending mode instead of Alpha, but it’s usually easier when you know exactly which pixels will be transparent and which won’t be.

6

Thanks for the info!

Cheers

Paul

7

See if you can make a basic soft shadow that you can sit just above the floor beneath a roughly spherical object.

In Gimp start a new image say 256 x 256. White background. Put a solid black circle in the center about 120 pixels in diameter.

Give it heaps of Gaussian blur almost to the edges of the image but make sure there is still some pure white at the edge.

On the color swatch on the toolbox, switch black with white.

Now somewhere on the main menu you’ll find “Color to Alpha”. Click that and you should see a nice smooth blend from black to transparent to use as a soft blob shadow. With a bit of trial and error you can save it as a png.

Then you’ll see how you can draw and blur other shapes to be the faked shadows of various objects. If the object’s stationary or just moves around on a flat surface you can parent the shadow or fade it or scale it if the object lifts off the floor.