🚀 go-pugleaf

In article <6omgsn$kgk$1@nnrp1.dejanews.com>, eduardo@fnn.net wrote:


>I'm a newbie programmer... and I need to find some algorithms to
>perform Alpha Blending...

Take a look at the book "High Performance Computer Imaging",
by Ihtisham Kabir, Manning Publications Co. 1996, pp. 150-153

It contains a C the algorithm you want, along with a lot of other
useful stuff.

You'll find below an example I wrote in C for performing alpha
blending with two input RGB pixels (in1 and in2) into an output
RGB pixel (out). Do not use this example "as is", it has been
written in order to provide a good clarity at the expense of
performance.

Hope this helps,

Nicolas Rudaz

--
#define R 0
#define G 1
#define B 2

long tmp[3];

/* 0 <= alpha, in1[i], in2[i], out[i] <= 255 */
unsigned char alpha, in1[3], in2[3], out[3];

tmp[R] = alpha * (in1[R] - in2[R]);
tmp[G] = alpha * (in1[G] - in2[G]);
tmp[B] = alpha * (in1[B] - in2[B]);

tmp[R] += in2[R] << 8;
tmp[G] += in2[G] << 8;
tmp[B] += in2[B] << 8;

out[R]   = (unsigned char) (tmp[R] >> 8);
out[G]   = (unsigned char) (tmp[G] >> 8);
out[B]   = (unsigned char) (tmp[B] >> 8);