drawLineCore()

template<typename PixelT, typename Coord, bool Overwrite>

void fl::gfx::detail::drawLineCore ( Canvas< PixelT > & canvas, const PixelT & color, Coord x0, Coord y0, Coord x1, Coord y1 )

inline

Definition at line 532 of file primitives.h.

                                                                              {
    PixelT* pixels = canvas.pixels;
    int width = canvas.width;
    int height = canvas.height;
 
    // Convert to 8.8 fixed-point
    fl::i32 fx0 = detail::toFixed8(x0);
    fl::i32 fy0 = detail::toFixed8(y0);
    fl::i32 fx1 = detail::toFixed8(x1);
    fl::i32 fy1 = detail::toFixed8(y1);
 
    bool steep = fl::abs(fy1 - fy0) > fl::abs(fx1 - fx0);
    if (steep) { fl::swap(fx0, fy0); fl::swap(fx1, fy1); }
    if (fx0 > fx1) { fl::swap(fx0, fx1); fl::swap(fy0, fy1); }
 
    fl::i32 dx8 = fx1 - fx0;
    fl::i32 dy8 = fy1 - fy0;
 
    // Gradient per pixel step in 8.8: (dy * 256) / dx
    fl::i32 gradient = (dx8 == 0) ? 0 : ((dy8 << 8) / dx8);
 
    // First endpoint: round x to nearest pixel boundary
    fl::i32 xend = (fx0 + 128) & ~0xFF;
    fl::i32 yend = fy0 + ((gradient * (xend - fx0)) >> 8);
    fl::i32 xgap = 256 - ((fx0 + 128) & 0xFF);  // rfpart(x0 + 0.5)
    int xpxl1 = xend >> 8;
    int ypxl1 = yend >> 8;
    fl::u8 yfrac1 = static_cast<fl::u8>(yend & 0xFF);
 
    // Second endpoint
    fl::i32 xend2 = (fx1 + 128) & ~0xFF;
    fl::i32 yend2 = fy1 + ((gradient * (xend2 - fx1)) >> 8);
    fl::i32 xgap2 = (fx1 + 128) & 0xFF;  // fpart(x1 + 0.5)
    int xpxl2 = xend2 >> 8;
    int ypxl2 = yend2 >> 8;
    fl::u8 yfrac2 = static_cast<fl::u8>(yend2 & 0xFF);
 
    // Draw first endpoint
    {
        fl::u8 b1 = static_cast<fl::u8>(((255 - yfrac1) * xgap) >> 8);
        fl::u8 b2 = static_cast<fl::u8>((yfrac1 * xgap) >> 8);
        if (steep) {
            PixelT c = color; c.nscale8(b1);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, ypxl1, xpxl1, c);
            c = color; c.nscale8(b2);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, ypxl1 + 1, xpxl1, c);
        } else {
            PixelT c = color; c.nscale8(b1);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, xpxl1, ypxl1, c);
            c = color; c.nscale8(b2);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, xpxl1, ypxl1 + 1, c);
        }
    }
 
    // Draw second endpoint
    {
        fl::u8 b1 = static_cast<fl::u8>(((255 - yfrac2) * xgap2) >> 8);
        fl::u8 b2 = static_cast<fl::u8>((yfrac2 * xgap2) >> 8);
        if (steep) {
            PixelT c = color; c.nscale8(b1);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, ypxl2, xpxl2, c);
            c = color; c.nscale8(b2);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, ypxl2 + 1, xpxl2, c);
        } else {
            PixelT c = color; c.nscale8(b1);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, xpxl2, ypxl2, c);
            c = color; c.nscale8(b2);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, xpxl2, ypxl2 + 1, c);
        }
    }
 
    // Main loop: integer counter, 8.8 intery accumulation
    fl::i32 intery = yend + gradient;
    if (steep) {
        for (int x = xpxl1 + 1; x < xpxl2; ++x) {
            int y = intery >> 8;
            fl::u8 frac = static_cast<fl::u8>(intery & 0xFF);
            PixelT c = color; c.nscale8(255 - frac);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, y, x, c);
            c = color; c.nscale8(frac);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, y + 1, x, c);
            intery += gradient;
        }
    } else {
        for (int x = xpxl1 + 1; x < xpxl2; ++x) {
            int y = intery >> 8;
            fl::u8 frac = static_cast<fl::u8>(intery & 0xFF);
            PixelT c = color; c.nscale8(255 - frac);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, x, y, c);
            c = color; c.nscale8(frac);
            addPixelToBuffer<PixelT, Overwrite>(pixels, width, height, x, y + 1, c);
            intery += gradient;
        }
    }
}

References fl::abs(), fl::gfx::addPixelToBuffer(), fl::FL_NO_EXCEPT, fl::height, fl::swap(), toFixed8(), fl::width, fl::x, and fl::y.

Referenced by fl::gfx::drawLine().

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