The application calls this function to get a set of hit-test metrics corresponding to a range of text positions. One of the main usages is to implement highlight selection of the text string. The function returns E_NOT_SUFFICIENT_BUFFER, which is equivalent to HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER), when the buffer size of hitTestMetrics is too small to hold all the regions calculated by the function. In this situation, the function sets the output value *actualHitTestMetricsCount to the number of geometries calculated. The application is responsible for allocating a new buffer of greater size and calling the function again. A good value to use as an initial value for maxHitTestMetricsCount may be calculated from the following equation: maxHitTestMetricsCount = lineCount * maxBidiReorderingDepth where lineCount is obtained from the value of the output argument *actualLineCount (from the function IDWriteTextLayout::GetLineLengths), and the maxBidiReorderingDepth value from the DWRITE_TEXT_METRICS structure of the output argument *textMetrics (from the function IDWriteFactory::CreateTextLayout).

'宣言
 
Public Overloads Function HitTestTextRange( _
   ByVal textPosition As System.Integer, _
   ByVal textLength As System.Integer, _
   ByVal originX As System.Single, _
   ByVal originY As System.Single _
) As HitTestMetrics()

public HitTestMetrics[] HitTestTextRange( 
   System.int textPosition,
   System.int textLength,
   System.float originX,
   System.float originY
)