IDWriteTextLayout::HitTestTextRange method (dwrite.h)

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).

Syntax

HRESULT HitTestTextRange(
                  UINT32                  textPosition,
                  UINT32                  textLength,
                  FLOAT                   originX,
                  FLOAT                   originY,
  [out, optional] DWRITE_HIT_TEST_METRICS *hitTestMetrics,
                  UINT32                  maxHitTestMetricsCount,
  [out]           UINT32                  *actualHitTestMetricsCount
);

Parameters

textPosition

Type: UINT32

The first text position of the specified range.

textLength

Type: UINT32

The number of positions of the specified range.

originX

Type: FLOAT

The origin pixel location X at the left of the layout box. This offset is added to the hit-test metrics returned.

originY

Type: FLOAT

The origin pixel location Y at the top of the layout box. This offset is added to the hit-test metrics returned.

[out, optional] hitTestMetrics

Type: DWRITE_HIT_TEST_METRICS*

When this method returns, contains a pointer to a buffer of the output geometry fully enclosing the specified position range. The buffer must be at least as large as maxHitTestMetricsCount.

maxHitTestMetricsCount

Type: UINT32

Maximum number of boxes hitTestMetrics could hold in its buffer memory.

[out] actualHitTestMetricsCount

Type: UINT32*

Actual number of geometries hitTestMetrics holds in its buffer memory.

Return value

Type: HRESULT

If this method succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.

Requirements

See also

IDWriteTextLayout