bresenhamDrawLineUnsafe.cpp

constexpr size_t indexOf(int x, int y, int stride)
{
    return static_cast<size_t>(x + y * stride);
}

template <typename RGB>
void bresenhamDrawLineUnsafe(RGB *buffer, int w, int h, int x0, int y0, int x1, int y1, RGB rgb)
{
    const auto dx = x1 - x0, dy = y1 - y0;
    const auto dxSign = mve::math::sgn(dx), dySign = mve::math::sgn(dy);
    const auto dxAbs = std::abs(dx), dyAbs = std::abs(dy);
    const auto dmax = std::max(dx, dy, [](auto lhs, auto rhs) {
        return std::abs(lhs) < std::abs(rhs);
    });
    auto err = std::abs(dmax / 2);

#define DRAW(x, y) buffer[indexOf(x, y, w)] = rgb;
    if (dmax == dx) {
        for (int x = x0, y = y0; x != x1; x += dxSign) {
            DRAW(x, y);

            err -= dyAbs;
            if (err < 0) {
                err += dxAbs;
                y += dySign;
            }
        }
    }
    else if (dmax == dy) {
        for (int x = x0, y = y0; y != y1; y += dySign) {
            DRAW(x, y);

            err -= dxAbs;
            if (err < 0) {
                err += dyAbs;
                x += dxSign;
            }
        }
    }
#undef DRAW
}