void NatePixTable::Frame::load_overlay(const PixMap& pix, uint8_t color) {
for (auto x : range(width())) {
for (auto y : range(height())) {
RgbColor over = pix.get(x, y);
uint8_t value = over.red;
uint8_t frac = over.alpha;
over = RgbColor::tint(color, value);
RgbColor under = _pix_map.get(x, y);
RgbColor composite;
composite.red = ((over.red * frac) + (under.red * (255 - frac))) / 255;
composite.green = ((over.green * frac) + (under.green * (255 - frac))) / 255;
composite.blue = ((over.blue * frac) + (under.blue * (255 - frac))) / 255;
composite.alpha = under.alpha;
_pix_map.set(x, y, composite);
}
}
}
void PixMap::composite(const PixMap& pix) {
if (size() != pix.size()) {
throw Exception("Mismatch in PixMap sizes");
}
for (int y = 0; y < size().height; ++y) {
for (int x = 0; x < size().width; ++x) {
const RgbColor& over = pix.get(x, y);
const double oa = over.alpha / 255.0;
const RgbColor& under = get(x, y);
const double ua = under.alpha / 255.0;
// TODO(sfiera): if we're going to do anything like this in the long run, we should
// require that alpha be pre-multiplied with the color components. We should probably
// also use integral arithmetic.
double red = (over.red * oa) + ((under.red * ua) * (1.0 - oa));
double green = (over.green * oa) + ((under.green * ua) * (1.0 - oa));
double blue = (over.blue * oa) + ((under.blue * ua) * (1.0 - oa));
double alpha = oa + (ua * (1.0 - oa));
set(x, y, RgbColor(alpha * 255, red / alpha, green / alpha, blue / alpha));
}
}
}