Semi-transparent image?

How would you make part of an image semi-transparent in 2d?
Meaning like you can see the image(meaning maskimage wont work), but you can also see whats under it. I need to use it for a glow effect, because I have a glowing bullet, and the glow outline around it shows, and blocks out the background(which looks weird) How would I make it so that you can see the glow but also the background?

In 3D, I suppose. I'm not sure if you can use 2D images with 'alpha'. However, using 3D to simulate 2D should work.

Hmm, I really need it to be 2d. But thanks anyway.

I heard somwhere that one of the image formats support alpha. Anyone know if thats true and if so which one?

PNG and TGA support alpha but the alpha bits are not used for 2d images. You'll need to use textures unless there is a 3d party library out there.

I'm not sure, but i think, if you make a .bmp file, the black parts of the image are invisible. I made something like a glow effect to, and it worked fine.

In 2d if you are trying to perform alpha blending (transparency) then you will need to use the writepixelfast/readpixelfast commands - first read the background image's pixel color components (it may be stored in a bank or array for a reasonable speed increase), read the pixel color of the pixel in the image you want to alpha blend, calculate the new red/green/blue components values based on these figures and the alpha value for the pixel (this could also be all stored in an array or bank for a reasonable speed increase) then you will need to draw the resulting pixel with writepixelfast.

This obviously means you have to iterate through all the pixels in the image - however one way you can optimise it by not performing the calculation for pixels which are completely transparent or completely opaque.

something like this :

(I may have taken some of this from the code archives a long time ago, it is very useful)

RGB=readpixelfast(x,y,imagebuffer(your image handle goes here))
BRGB=readpixelfast(x,y,backbuffer()) ;background rgb value
Alpha#=0.5 ;for example 50% transparent.
;if you want each pixel to have its own Alpha value you will need to store this yourself as blitz3d/blitzplus in 2d cannot read the alpha values using the readpixel commands, however you can store them in a bank by either creating your own image format or by obtaining the alpha values from the image files directly when loading
		
bR = (BRGB Shr 16) And 255
bG = (BRGB Shr 8 ) And 255
bB = (BRGB       ) And 255
dR = Float(((RGB Shr 16) And 255) - bR)*Alpha#  
dG = Float(((RGB Shr 8 ) And 255) - bG)*Alpha#
dB = Float(((RGB       ) And 255) - bB)*Alpha#
RGB=((bR+dR) Shl 16) Or ((bG+dG) Shl 8) Or (bB+dB)
				
writepixelfast x,y,RGB,backbuffer()

Something like that should get you started..

you can also make some of the pixels black
(mask color) so that you can see through it