MGL_stretchBltCoord

Stretches a block of image data from one device context to another.

Declaration

void MGLAPI MGL_stretchBltCoord(
MGLDC *dst,
MGLDC *src,
int left,
int top,
int right,
int bottom,
int dstLeft,
int dstTop,
int dstRight,
int dstBottom,
int op)

Prototype In

mgraph.h

Parameters

dst | Destination device context
src | Source device context
left | Left coordinate of source image
top | Top coordinate of source image
right | Right coordinate of source image
bottom | Bottom coordinate of source image
dstLeft | Left coordinate of destination image
dstTop | Top coordinate of destination image
dstRight | Right coordinate of destination image
dstBottom | Bottom coordinate of destination image
op | Write mode to use during Blt

Description

Copies a block of bitmap data form one device context to another, stretching or shrinking the image as necessary to fit the destination rectangle for the destination device context.

The source and destination device context may be the same, however the source and destination rectangles may not overlap. This routine has been highly optimized for absolute maximum performance, so it will provide the fastest method of stretching bitmap data between device contexts, and can also be used to stretch bitmap data from a memory device context to a windowed device context.

This function will correctly handle StretchBlt's across device contexts with differing pixel depths, and will perform the necessary pixel format translation to convert from the source device to the destination device. Note that although the code to implement this is highly optimized, this can be a time consuming operation so you should attempt to pre-convert all bitmaps to the current display device pixel format for maximum performance if possible.

When this 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 this function is 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.

The source and destination rectangles are clipped according to the current clipping rectangles for the source and destination device contexts respectively, however the zoom factor is determined using the unclipped source and destination rectangles.

See Also

MGL_bitBlt, MGL_bitBltCoord, MGL_srcTransBlt, MGL_srcTransBltCoord, MGL_dstTransBlt, MGL_dstTransBltCoord, MGL_bitBltPatt, MGL_bitBltPattCoord, MGL_bitBltFx, MGL_bitBltFxCoord, MGL_stretchBlt, MGL_stretchBltCoord, MGL_stretchBltFx, MGL_stretchBltFxCoord, MGL_copyPage, MGL_copyPageCoord

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