305 lines
9.7 KiB
C++
305 lines
9.7 KiB
C++
#pragma once
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/*
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Amanatides–Woo grid traversal algorithm in C++.
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Given a line defined by two points, this algorithm traverses the grid cells
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intersecting the line and calls a visitor function for each cell.
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*/
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#include "fl/math.h"
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#include "fl/point.h"
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#include "fl/int.h"
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namespace fl {
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/// @brief Traverse a grid segment by selecting the cells that are crossed. This
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/// version will select the fastest integer implementation based on the length
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/// of the segment. Most of the time it will call traverseGridSegment16() since
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/// segment spans are typically < 256 pixels.
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/// @tparam GridVisitor
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/// @param start start point
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/// @param end end point
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/// @param visitor called for each cell visited.
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/// @details Fully tested.
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template <typename GridVisitor>
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void traverseGridSegment(const vec2f &start, const vec2f &end,
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GridVisitor &visitor);
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/// @brief Traverse a grid segment using fixed-point 8.8 arithmetic.
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/// @tparam GridVisitor
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/// @param start start point
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/// @param end end point
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/// @param visitor called for each cell visited.
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/// @details UNTESTED!!!!
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template <typename GridVisitor>
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void traverseGridSegment16(const vec2f &start, const vec2f &end,
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GridVisitor &visitor);
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// @brief Traverse a grid segment using fixed-point 24.8 arithmetic.
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/// @tparam GridVisitor
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/// @param start start point
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/// @param end end point
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/// @param visitor called for each cell visited.
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/// @details UNTESTED!!!!
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template <typename GridVisitor>
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void traverseGridSegment32(const vec2f &start, const vec2f &end,
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GridVisitor &visitor);
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/// @brief Traverse a grid segment using floating point arithmetic. Useful for
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/// testing.
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/// @tparam GridVisitor
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/// @param start start point
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/// @param end end point
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/// @param visitor called for each cell visited.
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/// @details Fully tested.
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template <typename GridVisitor>
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void traverseGridSegmentFloat(const vec2f &start, const vec2f &end,
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GridVisitor &visitor);
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////////////////////////// IMPLEMENTATION DETAILS //////////////////////////
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/// @brief Traverse a grid segment using fixed-point 8.8 arithmetic.
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/// @tparam GridVisitor
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/// @param start start point
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/// @param end end point
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/// @param visitor called for each cell visited.
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/// @details Fully tested.
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template <typename GridVisitor>
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inline void traverseGridSegmentFloat(const vec2f &start, const vec2f &end,
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GridVisitor &visitor) {
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int x0 = static_cast<int>(fl::floor(start.x));
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int y0 = static_cast<int>(fl::floor(start.y));
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int x1 = static_cast<int>(fl::floor(end.x));
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int y1 = static_cast<int>(fl::floor(end.y));
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int stepX = (x1 > x0) ? 1 : (x1 < x0) ? -1 : 0;
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int stepY = (y1 > y0) ? 1 : (y1 < y0) ? -1 : 0;
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float dx = end.x - start.x;
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float dy = end.y - start.y;
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float tDeltaX = (dx != 0.0f) ? ABS(1.0f / dx) : FLT_MAX;
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float tDeltaY = (dy != 0.0f) ? ABS(1.0f / dy) : FLT_MAX;
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float nextX = (stepX > 0) ? (fl::floor(start.x) + 1) : fl::floor(start.x);
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float nextY = (stepY > 0) ? (fl::floor(start.y) + 1) : fl::floor(start.y);
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float tMaxX = (dx != 0.0f) ? ABS((nextX - start.x) / dx) : FLT_MAX;
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float tMaxY = (dy != 0.0f) ? ABS((nextY - start.y) / dy) : FLT_MAX;
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float maxT = 1.0f;
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int currentX = x0;
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int currentY = y0;
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while (true) {
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visitor.visit(currentX, currentY);
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float t = MIN(tMaxX, tMaxY);
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if (t > maxT)
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break;
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if (tMaxX < tMaxY) {
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tMaxX += tDeltaX;
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currentX += stepX;
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} else {
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tMaxY += tDeltaY;
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currentY += stepY;
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}
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}
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// Ensure the end cell (x1, y1) is visited at least once
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if (currentX != x1 || currentY != y1) {
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visitor.visit(x1, y1);
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}
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}
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/// @brief Traverse a grid segment using fixed-point 8.8 arithmetic.
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/// @tparam GridVisitor
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/// @param start start point
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/// @param end end point
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/// @param visitor called for each cell visited.
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/// @details UNTESTED!!!!
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template <typename GridVisitor>
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inline void traverseGridSegment16(const vec2f &start, const vec2f &end,
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GridVisitor &visitor) {
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const i16 FP_SHIFT = 8;
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const i16 FP_ONE = 1 << FP_SHIFT;
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// const i16 FP_MASK = FP_ONE - 1;
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// Convert to fixed-point (Q8.8), signed
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i16 startX_fp = static_cast<i16>(start.x * FP_ONE);
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i16 startY_fp = static_cast<i16>(start.y * FP_ONE);
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i16 endX_fp = static_cast<i16>(end.x * FP_ONE);
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i16 endY_fp = static_cast<i16>(end.y * FP_ONE);
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i16 x0 = startX_fp >> FP_SHIFT;
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i16 y0 = startY_fp >> FP_SHIFT;
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i16 x1 = endX_fp >> FP_SHIFT;
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i16 y1 = endY_fp >> FP_SHIFT;
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i16 stepX = (x1 > x0) ? 1 : (x1 < x0) ? -1 : 0;
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i16 stepY = (y1 > y0) ? 1 : (y1 < y0) ? -1 : 0;
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i16 deltaX_fp = endX_fp - startX_fp;
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i16 deltaY_fp = endY_fp - startY_fp;
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u16 absDeltaX_fp =
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(deltaX_fp != 0) ? static_cast<u16>(
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ABS((i32(FP_ONE) << FP_SHIFT) / deltaX_fp))
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: UINT16_MAX;
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u16 absDeltaY_fp =
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(deltaY_fp != 0) ? static_cast<u16>(
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ABS((i32(FP_ONE) << FP_SHIFT) / deltaY_fp))
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: UINT16_MAX;
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i16 nextX_fp = (stepX > 0) ? ((x0 + 1) << FP_SHIFT) : (x0 << FP_SHIFT);
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i16 nextY_fp = (stepY > 0) ? ((y0 + 1) << FP_SHIFT) : (y0 << FP_SHIFT);
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u16 tMaxX_fp =
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(deltaX_fp != 0)
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? static_cast<u16>(
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ABS(i32(nextX_fp - startX_fp)) * absDeltaX_fp >> FP_SHIFT)
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: UINT16_MAX;
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u16 tMaxY_fp =
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(deltaY_fp != 0)
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? static_cast<u16>(
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ABS(i32(nextY_fp - startY_fp)) * absDeltaY_fp >> FP_SHIFT)
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: UINT16_MAX;
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const u16 maxT_fp = FP_ONE;
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i16 currentX = x0;
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i16 currentY = y0;
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while (true) {
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visitor.visit(currentX, currentY);
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u16 t_fp = (tMaxX_fp < tMaxY_fp) ? tMaxX_fp : tMaxY_fp;
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if (t_fp > maxT_fp)
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break;
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if (tMaxX_fp < tMaxY_fp) {
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tMaxX_fp += absDeltaX_fp;
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currentX += stepX;
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} else {
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tMaxY_fp += absDeltaY_fp;
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currentY += stepY;
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}
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}
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// Ensure the end cell (x1, y1) is visited at least once
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if (currentX != x1 || currentY != y1) {
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visitor.visit(x1, y1);
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}
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}
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// @brief Traverse a grid segment using fixed-point 24.8 arithmetic.
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/// @tparam GridVisitor
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/// @param start start point
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/// @param end end point
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/// @param visitor called for each cell visited.
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/// @details UNTESTED!!!!
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template <typename GridVisitor>
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inline void traverseGridSegment32(const vec2f &start, const vec2f &end,
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GridVisitor &visitor) {
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const i32 FP_SHIFT = 8;
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const i32 FP_ONE = 1 << FP_SHIFT;
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// const i32 FP_MASK = FP_ONE - 1;
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// Convert to fixed-point (Q24.8) signed
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i32 startX_fp = static_cast<i32>(start.x * FP_ONE);
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i32 startY_fp = static_cast<i32>(start.y * FP_ONE);
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i32 endX_fp = static_cast<i32>(end.x * FP_ONE);
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i32 endY_fp = static_cast<i32>(end.y * FP_ONE);
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i32 x0 = startX_fp >> FP_SHIFT;
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i32 y0 = startY_fp >> FP_SHIFT;
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i32 x1 = endX_fp >> FP_SHIFT;
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i32 y1 = endY_fp >> FP_SHIFT;
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i32 stepX = (x1 > x0) ? 1 : (x1 < x0) ? -1 : 0;
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i32 stepY = (y1 > y0) ? 1 : (y1 < y0) ? -1 : 0;
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i32 deltaX_fp = endX_fp - startX_fp;
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i32 deltaY_fp = endY_fp - startY_fp;
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u32 absDeltaX_fp =
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(deltaX_fp != 0) ? static_cast<u32>(
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ABS((fl::i64(FP_ONE) << FP_SHIFT) / deltaX_fp))
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: UINT32_MAX;
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u32 absDeltaY_fp =
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(deltaY_fp != 0) ? static_cast<u32>(
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ABS((fl::i64(FP_ONE) << FP_SHIFT) / deltaY_fp))
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: UINT32_MAX;
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i32 nextX_fp = (stepX > 0) ? ((x0 + 1) << FP_SHIFT) : (x0 << FP_SHIFT);
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i32 nextY_fp = (stepY > 0) ? ((y0 + 1) << FP_SHIFT) : (y0 << FP_SHIFT);
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u32 tMaxX_fp =
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(deltaX_fp != 0)
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? static_cast<u32>(
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ABS(fl::i64(nextX_fp - startX_fp)) * absDeltaX_fp >> FP_SHIFT)
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: UINT32_MAX;
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u32 tMaxY_fp =
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(deltaY_fp != 0)
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? static_cast<u32>(
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ABS(fl::i64(nextY_fp - startY_fp)) * absDeltaY_fp >> FP_SHIFT)
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: UINT32_MAX;
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const u32 maxT_fp = FP_ONE;
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i32 currentX = x0;
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i32 currentY = y0;
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while (true) {
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visitor.visit(currentX, currentY);
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u32 t_fp = (tMaxX_fp < tMaxY_fp) ? tMaxX_fp : tMaxY_fp;
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if (t_fp > maxT_fp)
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break;
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if (tMaxX_fp < tMaxY_fp) {
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tMaxX_fp += absDeltaX_fp;
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currentX += stepX;
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} else {
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tMaxY_fp += absDeltaY_fp;
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currentY += stepY;
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}
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}
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if (currentX != x1 || currentY != y1) {
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visitor.visit(x1, y1);
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}
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}
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template <typename GridVisitor>
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inline void traverseGridSegment(const vec2f &start, const vec2f &end,
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GridVisitor &visitor) {
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float dx = ABS(end.x - start.x);
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float dy = ABS(end.y - start.y);
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float maxRange = MAX(dx, dy);
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// if (maxRange < 256.0f) {
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// // Use Q8.8 (16-bit signed) if within ±127
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// traverseGridSegment16(start, end, visitor);
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// }
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// else if (maxRange < 16777216.0f) {
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// // Use Q24.8 (32-bit signed) if within ±8 million
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// traverseGridSegment32(start, end, visitor);
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// }
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// else {
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// // Fall back to floating-point
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// traverseGridSegment(start, end, visitor);
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// }
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if (maxRange < 256.0f) {
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// Use Q8.8 (16-bit signed) if within ±127
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traverseGridSegment16(start, end, visitor);
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} else {
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// Use Q24.8 (32-bit signed) if within ±8 million
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traverseGridSegment32(start, end, visitor);
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}
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}
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} // namespace fl
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