read call of the associated ImageReader. The degree of completion is expressed as a percentage varying from 0.0F to 100.0F. The percentage should ideally be calculated in terms of the remaining time to completion, but it is usually more practical to use a more well-defined metric such as pixels decoded or portion of input stream consumed. In any case, a sequence of calls to this method during a given read operation should supply a monotonically increasing sequence of percentage values. It is not necessary to supply the exact values 0 and 100, as these may be inferred by the callee from other methods.
Each particular ImageReader implementation may call this method at whatever frequency it desires. A rule of thumb is to call it around each 5 percent mark.
@param source the ImageReader object calling this method.
@param percentageDone the approximate percentage of decoding thathas been completed.
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