THPDFRandomAccessSource.IsRangeAvailable Method

Tells you whether the byte range starting at Offset for Count bytes sits wholly inside the source size

Declaration

function IsRangeAvailable(Offset, Count: Int64): boolean; virtual;

HPDFDoc

Name	Purpose
`Offset`	Zero-based byte offset at which the range starts
`Count`	Length of the range in bytes

True where both offsets are non-negative and the whole range fits inside GetSize, otherwise False

The base implementation works the answer out from GetSize alone, so it cannot tell whether a truncated remote file has actually delivered the bytes yet
Override this method in custom sources that keep track of arrived byte ranges, for instance linearized or partially downloaded input
Callers such as the linearized redraw scheduler use it to decide when a first-paint or dependency range may be read