IWICProgressiveLevelControl::SetCurrentLevel method (wincodec.h)

Specifies the level to retrieve on the next call to CopyPixels.

Syntax

HRESULT SetCurrentLevel(
  [in] UINT nLevel
);

Parameters

[in] nLevel

Type: UINT

Specifies which level to return next. If greater than the total number of levels supported, an error will be returned.

Return value

Type: HRESULT

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

Remarks

A call does not have to request every level supported. If a caller requests level 1, without having previously requested level 0, the bits returned by the next call to CopyPixels will include both levels.

If the requested level is invalid, the error returned is WINCODEC_ERR_INVALIDPROGRESSIVELEVEL.

Examples

Users should use this method to iterate through the progressive levels of a progressive JPEG image rather than the GetCurrentLevel method. JPEG progressive levels are determined by the image and do not have a fixed level count. Using GetCurrentLevel method will force the application to wait for all progressive levels to be downloaded before it can return. Instead, applications should use the following code to iterate through the progressive levels of a progressive JPEG image.

IWICProgressiveLevelControl *pProgressive = NULL;

HRESULT hr = (pBitmapFrame->QueryInterface(
   IID_IWICProgressiveLevelControl, 
   (void**) &pProgressive));
                
if (SUCCEEDED(hr))
{
   for (UINT uCurrentLevel = 0; SUCCEEDED(hr); uCurrentLevel++)
   {
      hr = pProgressive->SetCurrentLevel(uCurrentLevel);
      if (WINCODEC_ERR_INVALIDPROGRESSIVELEVEL == hr)
      {
         // No more levels
         break;
      }

      if (SUCCEEDED(hr))
      {
         // Output the current level
         hr = pBitmapFrame->CopyPixels(...);
      }                      
   }
}

if (pProgressive)
{
   pProgressive->Release();
}	

Requirements

See also

IWICProgressiveLevelControl

Progressive Decoding Overview