downscaleArbitrary()

void fl::downscaleArbitrary	(	const CRGB *	src,
		const XYMap &	srcXY,
		CRGB *	dst,
		const XYMap &	dstXY )

Definition at line 82 of file downscale.cpp.

                                            {
    const fl::u16 srcWidth = srcXY.getWidth();
    const fl::u16 srcHeight = srcXY.getHeight();
    const fl::u16 dstWidth = dstXY.getWidth();
    const fl::u16 dstHeight = dstXY.getHeight();
 
    const fl::u32 FP_ONE = 256; // Q8.8 fixed-point multiplier
 
    FASTLED_ASSERT(dstWidth <= srcWidth,
                   "Destination width must be <= source width");
    FASTLED_ASSERT(dstHeight <= srcHeight,
                   "Destination height must be <= source height");
 
    for (fl::u16 dy = 0; dy < dstHeight; ++dy) {
        // Fractional boundaries in Q8.8
        fl::u32 dstY0 = (dy * srcHeight * FP_ONE) / dstHeight;
        fl::u32 dstY1 = ((dy + 1) * srcHeight * FP_ONE) / dstHeight;
 
        for (fl::u16 dx = 0; dx < dstWidth; ++dx) {
            fl::u32 dstX0 = (dx * srcWidth * FP_ONE) / dstWidth;
            fl::u32 dstX1 = ((dx + 1) * srcWidth * FP_ONE) / dstWidth;
 
            fl::u64 rSum = 0, gSum = 0, bSum = 0;
            fl::u32 totalWeight = 0;
 
            // Find covered source pixels
            fl::u16 srcY_start = dstY0 / FP_ONE;
            fl::u16 srcY_end = (dstY1 + FP_ONE - 1) / FP_ONE; // ceil
 
            fl::u16 srcX_start = dstX0 / FP_ONE;
            fl::u16 srcX_end = (dstX1 + FP_ONE - 1) / FP_ONE; // ceil
 
            for (fl::u16 sy = srcY_start; sy < srcY_end; ++sy) {
                // Calculate vertical overlap in Q8.8
                fl::u32 sy0 = sy * FP_ONE;
                fl::u32 sy1 = (sy + 1) * FP_ONE;
                fl::u32 y_overlap = MIN(dstY1, sy1) - MAX(dstY0, sy0);
                if (y_overlap == 0)
                    continue;
 
                for (fl::u16 sx = srcX_start; sx < srcX_end; ++sx) {
                    fl::u32 sx0 = sx * FP_ONE;
                    fl::u32 sx1 = (sx + 1) * FP_ONE;
                    fl::u32 x_overlap = MIN(dstX1, sx1) - MAX(dstX0, sx0);
                    if (x_overlap == 0)
                        continue;
 
                    fl::u32 weight = (x_overlap * y_overlap + (FP_ONE >> 1)) >>
                                      8; // Q8.8 * Q8.8 → Q16.16 → Q8.8
 
                    const CRGB &p = src[srcXY.mapToIndex(sx, sy)];
                    rSum += p.r * weight;
                    gSum += p.g * weight;
                    bSum += p.b * weight;
                    totalWeight += weight;
                }
            }
 
            // Final division, rounding
            fl::u8 r =
                totalWeight ? (rSum + (totalWeight >> 1)) / totalWeight : 0;
            fl::u8 g =
                totalWeight ? (gSum + (totalWeight >> 1)) / totalWeight : 0;
            fl::u8 b =
                totalWeight ? (bSum + (totalWeight >> 1)) / totalWeight : 0;
 
            dst[dstXY.mapToIndex(dx, dy)] = CRGB(r, g, b);
        }
    }
}

References fl::XYMap::getHeight(), fl::XYMap::getWidth(), fl::XYMap::mapToIndex(), MAX, and MIN.

Referenced by downscale().

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