Color Keys

Transparency

To use:

· decide on a transparent color (color index, a number, or range of transparent colors), usually RGB (0,0,0) or index 0.

· Create a DDCOLORKEY key

· Set the transparent color range

· Add DDSD_CKSRCBLT OR DDSD_CKDESTBLT to the surface dwFlags

· Then blt will copy everything but those pixels.

2 ways to perform transparency:

source transparency – designate colors in the source image that are not to be blitted. USE THIS METHOD.

To set up source transparency use:

DDCOLORKEY key; // define color key

// make index color 0 transparent

key.dwColorSpaceLowValue = 0; // starting transparent color

key.dwColorSpaceHighValue = 0; // ending transparent color

//set the key on source surface (usually backbuffer)

lpdsback->SetColorKey(DDCKEY_SRCBLT, &key);

· Low & high values specify a range of transparent colors (set the same for single color).

· key.dwColorSpaceLowValue = RGB(128,0,0);
key.dwColorSpaceHighValue = RGB(255, 0,0);

· if a color range is needed use:

lpdsback->SetColorKey(DDCKEY_SRCBLT | DDCKEY_COLORSPACE, &key);

destination transparency – designate colors in the destination image that can not be blitted over (replaced). HAL only feature.

Almost the same as source except you designate the colors that can be replaced:

DDCOLORKEY key;

key.dwColorSpaceLowValue = 0; // starting drawable color

key.dwColorSpaceHighValue = 0; // ending drawable color

//set the key on source surface (usually backbuffer)

lpdsback->SetColorKey(DDCKEY_SRCBLT, &key);