Is the discharge of semen upon waking without masturbation or imagining, while striving against one's desires, considered to be in the same category as masturbation, and does it invalidate a voluntary fast?

If semen is discharged while awake without the person's will, despite their attempt to prevent it and their arousal, then there is nothing against them and their fast is valid. This is because the emission of semen does not invalidate the fast unless it occurs by the person's choice, such as masturbation by hand, or as a result of kissing and similar acts.