How to set up alpha blending to correct for dark edges?

beginners
#1

Hello!

I’m drawing a bunch of particles that have a fragment shader defined like this:

outputColor.rgb = someColor.rgb;
outputColor.a = 1. - smoothstep(0.25, 0.45, distFromCenter);

and blending set up like this

glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

and I almost get what I expected, circles with smooth, but dark edges. As if the blending with the background somehow darkens the color.

image

Any tips on how to approach this?
Thanks

#2

How should it look like? I mean what is that you are looking for?

#3

Let me show you how the above image looks if I set the alpha to 100% (in this case it won’t be a circle, but a completely opaque square).

image

The edges between the shapes blend perfectly (I mean, there is no blending, because alpha for each shape is 100%).

But if start fading the edges (with alpha), it all falls apart, look:

image

#4

How are you drawing each circle? and how is the blend happening?
can you try calling
ofEnableBlendMode(OF_BLENDMODE_ALPHA);
instead of the GL call you are using?
if it does not work try the other blend modes

///
///     OF_BLENDMODE_DISABLED
///     OF_BLENDMODE_ALPHA
///     OF_BLENDMODE_ADD
///     OF_BLENDMODE_SUBTRACT
///     OF_BLENDMODE_MULTIPLY
///     OF_BLENDMODE_SCREEN
///

I recall seeing something similar in the forum. try searching for issues with blending and alpha.