THPDFRandomAccessSource.IsRangeAvailable Method

Reports whether the byte range starting at Offset for Count bytes lies completely inside the source size

Declaration

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

HPDFDoc

Name	Purpose
`Offset`	Zero-based byte offset of the range start
`Count`	Range length in bytes

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

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