# What's the meaning of GL\_ONE\_MINUS\_SRC1\_ALPHA?

**URL:** <https://community.khronos.org/t/whats-the-meaning-of-gl-one-minus-src1-alpha/111989>\
**Category:** OpenGL: Advanced Coding\
**Tags:** opengles\
**Created:** [July 22, 2025, 7:46am UTC](https://community.khronos.org/t/whats-the-meaning-of-gl-one-minus-src1-alpha/111989 "2025-07-22T07:46:26Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![gpu22](https://community.khronos.org/letter_avatar_proxy/v4/letter/g/919ad9/32.png) [@gpu22](https://community.khronos.org/u/gpu22)\
**Post date:** [July 22, 2025, 7:46am UTC](https://community.khronos.org/t/whats-the-meaning-of-gl-one-minus-src1-alpha/111989/1 "2025-07-22T07:46:27Z")

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what’s the difference between GL\_ONE\_MINUS\_SRC1\_ALPHA and GL\_ONE\_MINUS\_SRC\_ALPHA ? Thanks!  
eg.  
glBlendFunc(GR\_GL\_ONE, GL\_ONE\_MINUS\_SRC\_ALPHA)  
glBlendFunc(GR\_GL\_ONE, GL\_ONE\_MINUS\_SRC1\_ALPHA)

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**Author:** ![Veryzon](https://community.khronos.org/user_avatar/community.khronos.org/veryzon/32/12266_2.png) [@Veryzon](https://community.khronos.org/u/Veryzon)\
**Post date:** [July 22, 2025, 8:23am UTC](https://community.khronos.org/t/whats-the-meaning-of-gl-one-minus-src1-alpha/111989/2 "2025-07-22T08:23:19Z")

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When dual-source blending is used (with multiple outputs from the fragment shader), you have two source, thus two alpha values.  
SRC\_ALPHA is the default and is assumed to be SRC0, which is gl\_FragData[0].a, and SRC1\_ALPHA is gl\_FragData[1].a.

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<div class="post-metadata">

**Author:** ![gpu22](https://community.khronos.org/letter_avatar_proxy/v4/letter/g/919ad9/32.png) [@gpu22](https://community.khronos.org/u/gpu22)\
**Post date:** [July 22, 2025, 11:43am UTC](https://community.khronos.org/t/whats-the-meaning-of-gl-one-minus-src1-alpha/111989/3 "2025-07-22T11:43:16Z")

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is there any demo for this? thanks! what’s the application scenarios of 2 outputs? what’s the max count of the output?

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**Author:** ![Dark\_Photon](https://community.khronos.org/user_avatar/community.khronos.org/dark_photon/32/4349_2.png) [@Dark\_Photon](https://community.khronos.org/u/Dark_Photon)\
**Post date:** [July 22, 2025, 12:32pm UTC](https://community.khronos.org/t/whats-the-meaning-of-gl-one-minus-src1-alpha/111989/4 "2025-07-22T12:32:04Z")

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> [@Dual source blending?!](https://community.khronos.org/t/dual-source-blending/76752):
>
> What exactly is dual source blending good for? Is it just for specific hardware that can get some more performance then doing it in a fragment shader? Or does it actually give some functionality that can not be done via shader and single source blending? Seems to be a very esoteric feature. But Vulkan implements it. I was hoping somebody here can tell me more about it?!

For examples, just web search for: “dual-source blending”.