traverseGridSegment16()

template<typename GridVisitor>

void fl::traverseGridSegment16 ( const vec2f & start, const vec2f & end, GridVisitor & visitor )

inline

Traverse a grid segment using fixed-point 8.8 arithmetic.

Template Parameters

GridVisitor

Parameters

start	start point
end	end point
visitor	called for each cell visited.

UNTESTED!!!!

Definition at line 122 of file traverse_grid.h.

                                                        {
    const int16_t FP_SHIFT = 8;
    const int16_t FP_ONE = 1 << FP_SHIFT;
    // const int16_t FP_MASK = FP_ONE - 1;
 
    // Convert to fixed-point (Q8.8), signed
    int16_t startX_fp = static_cast<int16_t>(start.x * FP_ONE);
    int16_t startY_fp = static_cast<int16_t>(start.y * FP_ONE);
    int16_t endX_fp = static_cast<int16_t>(end.x * FP_ONE);
    int16_t endY_fp = static_cast<int16_t>(end.y * FP_ONE);
 
    int16_t x0 = startX_fp >> FP_SHIFT;
    int16_t y0 = startY_fp >> FP_SHIFT;
    int16_t x1 = endX_fp >> FP_SHIFT;
    int16_t y1 = endY_fp >> FP_SHIFT;
 
    int16_t stepX = (x1 > x0) ? 1 : (x1 < x0) ? -1 : 0;
    int16_t stepY = (y1 > y0) ? 1 : (y1 < y0) ? -1 : 0;
 
    int16_t deltaX_fp = endX_fp - startX_fp;
    int16_t deltaY_fp = endY_fp - startY_fp;
 
    uint16_t absDeltaX_fp =
        (deltaX_fp != 0) ? static_cast<uint16_t>(
                               ABS((int32_t(FP_ONE) << FP_SHIFT) / deltaX_fp))
                         : UINT16_MAX;
    uint16_t absDeltaY_fp =
        (deltaY_fp != 0) ? static_cast<uint16_t>(
                               ABS((int32_t(FP_ONE) << FP_SHIFT) / deltaY_fp))
                         : UINT16_MAX;
 
    int16_t nextX_fp = (stepX > 0) ? ((x0 + 1) << FP_SHIFT) : (x0 << FP_SHIFT);
    int16_t nextY_fp = (stepY > 0) ? ((y0 + 1) << FP_SHIFT) : (y0 << FP_SHIFT);
 
    uint16_t tMaxX_fp =
        (deltaX_fp != 0)
            ? static_cast<uint16_t>(
                  ABS(int32_t(nextX_fp - startX_fp)) * absDeltaX_fp >> FP_SHIFT)
            : UINT16_MAX;
    uint16_t tMaxY_fp =
        (deltaY_fp != 0)
            ? static_cast<uint16_t>(
                  ABS(int32_t(nextY_fp - startY_fp)) * absDeltaY_fp >> FP_SHIFT)
            : UINT16_MAX;
 
    const uint16_t maxT_fp = FP_ONE;
 
    int16_t currentX = x0;
    int16_t currentY = y0;
 
    while (true) {
        visitor.visit(currentX, currentY);
 
        uint16_t t_fp = (tMaxX_fp < tMaxY_fp) ? tMaxX_fp : tMaxY_fp;
        if (t_fp > maxT_fp)
            break;
 
        if (tMaxX_fp < tMaxY_fp) {
            tMaxX_fp += absDeltaX_fp;
            currentX += stepX;
        } else {
            tMaxY_fp += absDeltaY_fp;
            currentY += stepY;
        }
    }
 
    // Ensure the end cell (x1, y1) is visited at least once
    if (currentX != x1 || currentY != y1) {
        visitor.visit(x1, y1);
    }
}

References ABS, fl::vec2< T >::x, and fl::vec2< T >::y.

Referenced by traverseGridSegment().

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