What's the meaning of GL_ONE_MINUS_SRC1_ALPHA?

OpenGL OpenGL: Advanced Coding
1

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)

2

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.

3

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

4

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