+ * The \c fragment.fogcoord input is used to compute the fog blend factor.
+ *
+ * \param ctx The GL context
+ * \param fprog Fragment program that fog instructions will be appended to.
+ * \param fog_mode Fog mode. One of \c GL_EXP, \c GL_EXP2, or \c GL_LINEAR.
+ * \param saturate True if writes to color outputs should be clamped to [0, 1]
+ *
+ * \note
+ * This function sets \c VARYING_BIT_FOGC in \c fprog->Base.InputsRead.
+ *
+ * \todo With a little work, this function could be adapted to add fog code