OpenGL - blending

0
votes

I have raycasting with this kind of color blending in for cycle in PS

 actual = <some color loaded from texture>;
 actual.a *= 0.05; //reduce the alpha to have a more transparent result 

 //Front to back blending  
 actual.rgb *= actual.a;
 last = (1.0 - last.a) * actual + last;

Can this equation be rewritten to use OpenGL 3 blending functions ? The goal is to remove cycle from PS by rendering more qauds over themselves

So far I am using this: glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA), but result looks different

EDIT:

last = cumulated color (aka. final color)    
actual = current color from texture
2
openglblending
Could you please clarify what last and and actual are? Is actual the current source color and last is the destination color, is last the current value in the framebuffer? - thokra
@thokra I have edited the question - Martin Perry

2 Answers

0
votes

The main problem is that you still have to premultiply the source color with the alpha value in your shader (actual.rgb *= actual.a).

I think for blending you have to use this function:

glBlendFunc(GL_ONE_MINUS_DST_ALPHA, GL_ONE);
glBlendEquation(GL_FUNC_ADD):
0
votes

glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) - by using this, you have formula like:

last.rgb = actual.a * actual.rgb + ( 1.0 - actual.a ) * last.rgb;

It's completely different from yours shader formula:

actual.rgb *= actual.a;

last = (1.0 - last.a) * actual + last;

So, you have different result.