- * Scan/rewrite program to remove reads of varying (output) registers.
- * In GLSL vertex shaders, varying vars can be read and written.
- * Normally, vertex varying vars are implemented as output registers.
+ * Scan/rewrite program to remove reads of custom (output) registers.
+ * The passed type has to be either PROGRAM_OUTPUT or PROGRAM_VARYING
+ * (for vertex shaders).
+ * In GLSL shaders, varying vars can be read and written.