Transparency with custom shader

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Hi,

I'm trying to control transparency (of parts of a mesh) with a fragment shader.

As a first test, I tried to adapt the deformable sphere example by changing the alpha value in deform_fs.glsl:

i.e. change

fragColor = vec4(finalColor, 1);

into

fragColor = vec4(finalColor, 0.5);

But it remains opaque.

Defining another visual in the sdf without shaders but with element <transparency>0.5</transparency> does yield a transparent object. Adding the <transparency> element to the visual with the shaders has no effect.

Is there a way to do this in the fragment shader?