MGL_checkIdentityPalette

Turns on or off identity palette checking.

Declaration

ibool MGLAPI MGL_checkIdentityPalette(
    ibool enable)

Prototype In

mgraph.h

Parameters

enable

True to enable identity palette checking, false to disable

 

Return Value

Old value of the identity palette check flag.

Description

Turns on or off the checking of identity palette mappings for MGL. This is a global flag, and by default, identity palette checking is turned on.

When any MGL blitting function is called for 4 and 8 bit source bitmaps being copied to either 4 or 8bpp destination device contexts, MGL first checks if the color palettes for the source and destination bitmaps are the same. If they are not, MGL translates the pixel values from the source bitmap to the destination color palette, looking for the closest match color if an exact match is not found. In order to obtain maximum performance for blt’ing bitmaps in color index modes, you should ensure that the color palette in the source device matches the color palette in the destination device to avoid on the fly palette translation. If you know in advance that the palette is identical for a series of blit operations, you can turn off all identity palette checking in MGL with the MGL_checkIdentityPalette function.

When any MGL blitting function called for 4 and 8 bit source bitmaps being copied to RGB destination device contexts, MGL will convert the pixels in the source bitmap using the source bitmap palette to map them to the destination pixel format. If however you know in advance that the palette for all source bitmaps is identical for a series of blit operations, you can use the MGL_checkIdentityPalette function to disable source palette translation. In this case the MGL will translate all color index bitmaps using the pre-defined color translation palette stored in the destination device context. You would then set the destination device context palette to the common palette for all blit operations using MGL_setPalette. If you are translating a lot of color index bitmaps, this will increase performance by avoiding the need to convert the palette entries to the destination pixel format for every blit operation.

See Also

MGL_bitBlt, MGL_stretchBlt, MGL_putBitmap

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