OpenGL Multiplicative Blending mode
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I'm trying to draw an image on top of a fully opaque background, using additive blending or multiplicative blending depending on a toggle.
Both work, but the alpha of the image gets ignored when doing multiplicative blending, while in additive it's working.
For additive I have:
glBlendFunc(GL_SRC_ALPHA, GL_ONE);
For multiplicative I have:
glBlendFunc(GL_DST_COLOR, GL_ZERO);
Additive works as expected, multiplicative ignores the alpha.
I am aware I can swap shaders to achieve what I want, but if I could do it through glBlendFunc it would be much better.
opengl
add a comment |
I'm trying to draw an image on top of a fully opaque background, using additive blending or multiplicative blending depending on a toggle.
Both work, but the alpha of the image gets ignored when doing multiplicative blending, while in additive it's working.
For additive I have:
glBlendFunc(GL_SRC_ALPHA, GL_ONE);
For multiplicative I have:
glBlendFunc(GL_DST_COLOR, GL_ZERO);
Additive works as expected, multiplicative ignores the alpha.
I am aware I can swap shaders to achieve what I want, but if I could do it through glBlendFunc it would be much better.
opengl
How should "multiplicative blending" incorporate the alpha?
– Nicol Bolas
Dec 30 '18 at 20:27
Maximum alpha should behave like it does, minimum alpha should leave the background unchanged, in the middle it should interpolate. It's what most image editing software does. Is it possible through glBlendFunc?
– evilpudding
Dec 30 '18 at 20:37
2
"in the middle it should interpolate" Interpolate between what and what? You want linear interpolation between two values, but one of them is neither the source nor destination colors. Write down the math you actually want done, and then see if that fits into OpenGL's blending math.
– Nicol Bolas
Dec 30 '18 at 20:45
final = dest.rgb * (1.0f - src.a) + (dest.rgb * src.rgb * src.a) I think it's this. Does it make sense?
– evilpudding
Dec 30 '18 at 20:55
When I said interpolate between them, I meant the maximum and minimum alpha states, wherealpha = 0
meant the image doesn't get drawn at all, andalpha = 1
isdest.rgb * src.rgb
, which is whatglBlendFunc(GL_DST_COLOR, GL_ZERO);
yields.
– evilpudding
Dec 30 '18 at 21:03
add a comment |
I'm trying to draw an image on top of a fully opaque background, using additive blending or multiplicative blending depending on a toggle.
Both work, but the alpha of the image gets ignored when doing multiplicative blending, while in additive it's working.
For additive I have:
glBlendFunc(GL_SRC_ALPHA, GL_ONE);
For multiplicative I have:
glBlendFunc(GL_DST_COLOR, GL_ZERO);
Additive works as expected, multiplicative ignores the alpha.
I am aware I can swap shaders to achieve what I want, but if I could do it through glBlendFunc it would be much better.
opengl
I'm trying to draw an image on top of a fully opaque background, using additive blending or multiplicative blending depending on a toggle.
Both work, but the alpha of the image gets ignored when doing multiplicative blending, while in additive it's working.
For additive I have:
glBlendFunc(GL_SRC_ALPHA, GL_ONE);
For multiplicative I have:
glBlendFunc(GL_DST_COLOR, GL_ZERO);
Additive works as expected, multiplicative ignores the alpha.
I am aware I can swap shaders to achieve what I want, but if I could do it through glBlendFunc it would be much better.
opengl
opengl
edited Jan 1 at 4:27
![](https://i.stack.imgur.com/tyWaU.png?s=32&g=1)
![](https://i.stack.imgur.com/tyWaU.png?s=32&g=1)
genpfault
41.9k95398
41.9k95398
asked Dec 30 '18 at 20:21
evilpuddingevilpudding
105
105
How should "multiplicative blending" incorporate the alpha?
– Nicol Bolas
Dec 30 '18 at 20:27
Maximum alpha should behave like it does, minimum alpha should leave the background unchanged, in the middle it should interpolate. It's what most image editing software does. Is it possible through glBlendFunc?
– evilpudding
Dec 30 '18 at 20:37
2
"in the middle it should interpolate" Interpolate between what and what? You want linear interpolation between two values, but one of them is neither the source nor destination colors. Write down the math you actually want done, and then see if that fits into OpenGL's blending math.
– Nicol Bolas
Dec 30 '18 at 20:45
final = dest.rgb * (1.0f - src.a) + (dest.rgb * src.rgb * src.a) I think it's this. Does it make sense?
– evilpudding
Dec 30 '18 at 20:55
When I said interpolate between them, I meant the maximum and minimum alpha states, wherealpha = 0
meant the image doesn't get drawn at all, andalpha = 1
isdest.rgb * src.rgb
, which is whatglBlendFunc(GL_DST_COLOR, GL_ZERO);
yields.
– evilpudding
Dec 30 '18 at 21:03
add a comment |
How should "multiplicative blending" incorporate the alpha?
– Nicol Bolas
Dec 30 '18 at 20:27
Maximum alpha should behave like it does, minimum alpha should leave the background unchanged, in the middle it should interpolate. It's what most image editing software does. Is it possible through glBlendFunc?
– evilpudding
Dec 30 '18 at 20:37
2
"in the middle it should interpolate" Interpolate between what and what? You want linear interpolation between two values, but one of them is neither the source nor destination colors. Write down the math you actually want done, and then see if that fits into OpenGL's blending math.
– Nicol Bolas
Dec 30 '18 at 20:45
final = dest.rgb * (1.0f - src.a) + (dest.rgb * src.rgb * src.a) I think it's this. Does it make sense?
– evilpudding
Dec 30 '18 at 20:55
When I said interpolate between them, I meant the maximum and minimum alpha states, wherealpha = 0
meant the image doesn't get drawn at all, andalpha = 1
isdest.rgb * src.rgb
, which is whatglBlendFunc(GL_DST_COLOR, GL_ZERO);
yields.
– evilpudding
Dec 30 '18 at 21:03
How should "multiplicative blending" incorporate the alpha?
– Nicol Bolas
Dec 30 '18 at 20:27
How should "multiplicative blending" incorporate the alpha?
– Nicol Bolas
Dec 30 '18 at 20:27
Maximum alpha should behave like it does, minimum alpha should leave the background unchanged, in the middle it should interpolate. It's what most image editing software does. Is it possible through glBlendFunc?
– evilpudding
Dec 30 '18 at 20:37
Maximum alpha should behave like it does, minimum alpha should leave the background unchanged, in the middle it should interpolate. It's what most image editing software does. Is it possible through glBlendFunc?
– evilpudding
Dec 30 '18 at 20:37
2
2
"in the middle it should interpolate" Interpolate between what and what? You want linear interpolation between two values, but one of them is neither the source nor destination colors. Write down the math you actually want done, and then see if that fits into OpenGL's blending math.
– Nicol Bolas
Dec 30 '18 at 20:45
"in the middle it should interpolate" Interpolate between what and what? You want linear interpolation between two values, but one of them is neither the source nor destination colors. Write down the math you actually want done, and then see if that fits into OpenGL's blending math.
– Nicol Bolas
Dec 30 '18 at 20:45
final = dest.rgb * (1.0f - src.a) + (dest.rgb * src.rgb * src.a) I think it's this. Does it make sense?
– evilpudding
Dec 30 '18 at 20:55
final = dest.rgb * (1.0f - src.a) + (dest.rgb * src.rgb * src.a) I think it's this. Does it make sense?
– evilpudding
Dec 30 '18 at 20:55
When I said interpolate between them, I meant the maximum and minimum alpha states, where
alpha = 0
meant the image doesn't get drawn at all, and alpha = 1
is dest.rgb * src.rgb
, which is what glBlendFunc(GL_DST_COLOR, GL_ZERO);
yields.– evilpudding
Dec 30 '18 at 21:03
When I said interpolate between them, I meant the maximum and minimum alpha states, where
alpha = 0
meant the image doesn't get drawn at all, and alpha = 1
is dest.rgb * src.rgb
, which is what glBlendFunc(GL_DST_COLOR, GL_ZERO);
yields.– evilpudding
Dec 30 '18 at 21:03
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How should "multiplicative blending" incorporate the alpha?
– Nicol Bolas
Dec 30 '18 at 20:27
Maximum alpha should behave like it does, minimum alpha should leave the background unchanged, in the middle it should interpolate. It's what most image editing software does. Is it possible through glBlendFunc?
– evilpudding
Dec 30 '18 at 20:37
2
"in the middle it should interpolate" Interpolate between what and what? You want linear interpolation between two values, but one of them is neither the source nor destination colors. Write down the math you actually want done, and then see if that fits into OpenGL's blending math.
– Nicol Bolas
Dec 30 '18 at 20:45
final = dest.rgb * (1.0f - src.a) + (dest.rgb * src.rgb * src.a) I think it's this. Does it make sense?
– evilpudding
Dec 30 '18 at 20:55
When I said interpolate between them, I meant the maximum and minimum alpha states, where
alpha = 0
meant the image doesn't get drawn at all, andalpha = 1
isdest.rgb * src.rgb
, which is whatglBlendFunc(GL_DST_COLOR, GL_ZERO);
yields.– evilpudding
Dec 30 '18 at 21:03