IMcRegionAccessFastAccess Property

Property Value

Type: Boolean

With FastAccess turned on (Ttrue), the pixel access functions GetLine and GetArea may return SAFEARRAYs that actually point to the image buffer. If FastAccess is False (its default state), the buffers returned by these functions contain copies of image data. FastAccess will honor a True assignment only when the client and the McRegionAccess object reside in the same address space (i.e., are running in the same process). In the case of GetArea, another requirement is that the accessed area be stored in one contiguous memory block. If the image is not stored in one contiguous buffer, and if GetLine succeeds in returning a pointer to image memory, this pointer is valid only until the next call to GetLine (since that line may be swapped out on the next call). Whether or not GetLine and GetArea use FastAccess mode, they always return the same type of SAFEARRAY. Therefore, clients need not handle these SAFEARRAY differently. The exception to this rule is when region masking is required. Since, with FastAccess on, GetLine and GetArea may return pointers to the actual image data, clients should be careful not to modify the value of pixels lying outside the mask. PutLine and PutArea check the pixel buffers that are passed to them. If these buffers represent actual image memory, they return immediately (any modified value would already have affected the image). Setting FastAccess to True does not force the RegionMask property to Nothing. However, masking is not performed on PutLine or PutArea if the source came from GetLine or GetArea in FastAccess mode. Under some circumstances where GetArea or GetLine is called indirectly from an out-of-process client, it may be safe to set FastAccess True because it is known that the Variant returned from GetArea/Line will only be used in the same process as the call to those methods. In this situation, you may force FastAccess to True by assigning to it the value mcpixbuf_cvbForceFastAccess.