CDrawImage::UpdateColourTable

The UpdateColourTable method updates the palette associated with a sample.

Syntax

void UpdateColourTable(
    HDC hdc,
    BITMAPINFOHEADER *pbmi
);

Parameters

hdc

Device context containing the sample image.

pbmi

Pointer to the BITMAPINFOHEADER structure containing the new palette.

Return Value

No return value.

Remarks

This member function is applicable only when using samples allocated through a CImageAllocator (or derived class) object. CImageAllocator creates samples that are created with the Microsoft Win32 CreateDIBSection function. When a palettized buffer is allocated through CreateDIBSection, a palette is passed in that is associated with that buffer.

Should the palette be changed, the new palette must be associated with the buffer before drawing it (this is done through the Win32 SetDIBColorTable function and internally with the UpdateColourTable member function). The drawing code knows to update the palette because the palette version it stores in the sample will differ from the palette version it keeps internally.

In essence, the sample gets an initial palette version when created. When the palette is changed (probably by a filter), it tells the draw object to increment its palette version (through the IncrementPaletteVersion member function). When the draw object next comes to draw the sample, it will see that the sample has an old palette version and will know to call UpdateColourTable on it.

The draw object knows the type of buffer used for samples through the NotifyAllocator member function. If it is called with TRUE, the buffers passed to it must be allocated by a CImageAllocator (or derived class) object. If it is called with FALSE, the buffers should be allocated in standard system memory (or other memory accessible to GDI in the same manner).

When the allocator is decommitted, it will typically delete all the samples it holds on to. When it is subsequently committed, the samples will be created again with their initial palette versions. At this point, the allocator should also reset the palette version in the draw object so that they remain in sync. An allocator can do this by calling the ResetPaletteVersion member function.

This is a protected member function.

See Also

• CDrawImage Class