OpenGl alpha test - How to replace AlphaFunc deprecated?

Question

I'm trying to draw sphere with alpha, but I have a problem with my Z-buffer. Some pixels are transparent but write in the Zbuffer so a pixel opaque just behind is hidden.

Here are my settings:

gl Enable: gl DEPTH_TEST.
gl DepthFunc: gl LEQUAL.
gl Disable: gl CULL_FACE.
gl Enable: gl BLEND. 
gl BlendFunc: gl SRC_ALPHA with: gl ONE_MINUS_SRC_ALPHA.

I know the function glAlphaFunc(GREATER, aFloat) and enable(ALPHA_TEST) can do that but I read that it's a deprecated function since 3.1 version of OpenGL. How can I do a correct render without using ALPHAFunc? Does someone know a trick, or a way to do this via shaders?

Answer 1

This is very easy to implement in a fragment shader, using the discard statement to prevent a fragment from being rendered:

uniform float alpha_threshold;

void main() {
    vec4 color = ...;
    
    if(color.a <= alpha_threshold) // Or whichever comparison here
        discard;
    
    gl_FragColor = color;
}