1 /* 2 * Copyright (C) 2024 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package androidx.ink.geometry 18 19 import androidx.annotation.FloatRange 20 import androidx.annotation.RestrictTo 21 import kotlin.math.hypot 22 23 /** Represents a directed line segment between two points. */ 24 public abstract class Segment internal constructor() { 25 public abstract val start: Vec 26 public abstract val end: Vec 27 28 /** The length of the [Segment]. */ 29 @FloatRange(from = 0.0) computeLengthnull30 public fun computeLength(): Float = hypot(start.x - end.x, start.y - end.y) 31 32 /** 33 * Returns an ImmutableVec with the displacement from start to end. This is equivalent to 34 * `subtract(end, start, output)`. 35 * 36 * For performance-sensitive code, prefer to use [computeDisplacement] with a pre-allocated 37 * instance of [MutableVec]. 38 */ 39 public fun computeDisplacement(): ImmutableVec = ImmutableVec(end.x - start.x, end.y - start.y) 40 41 /** 42 * Populates [outVec] with the displacement from start to end. This is equivalent to 43 * `subtract(end, start, output)`. Returns [outVec]. 44 */ 45 public fun computeDisplacement(outVec: MutableVec): MutableVec { 46 outVec.x = end.x - start.x 47 outVec.y = end.y - start.y 48 return outVec 49 } 50 51 /** 52 * Returns an [ImmutableVec] that lies halfway along the segment. 53 * 54 * For performance-sensitive code, prefer to use [computeMidpoint] with a pre-allocated instance 55 * of [MutableVec]. 56 */ computeMidpointnull57 public fun computeMidpoint(): ImmutableVec = 58 ImmutableVec((start.x + end.x) / 2, (start.y + end.y) / 2) 59 60 /** Populates [outVec] with the point halfway along the segment. */ 61 public fun computeMidpoint(outVec: MutableVec): MutableVec { 62 outVec.x = (start.x + end.x) / 2 63 outVec.y = (start.y + end.y) / 2 64 return outVec 65 } 66 67 /** 68 * Returns the minimum bounding box containing the [Segment]. 69 * 70 * For performance-sensitive code, prefer to use [computeBoundingBox] with a pre-allocated 71 * instance of [MutableBox]. 72 */ computeBoundingBoxnull73 public fun computeBoundingBox(): ImmutableBox { 74 // TODO(b/354236964): Optimize unnecessary allocations 75 val (minX, maxX, minY, maxY) = getBoundingXYCoordinates(this) 76 return ImmutableBox.fromTwoPoints(ImmutableVec(minX, minY), ImmutableVec(maxX, maxY)) 77 } 78 79 /** Populates [outBox] with the minimum bounding box containing the [Segment]. */ computeBoundingBoxnull80 public fun computeBoundingBox(outBox: MutableBox): MutableBox { 81 // TODO(b/354236964): Optimize unnecessary allocations 82 val (minX, maxX, minY, maxY) = getBoundingXYCoordinates(this) 83 outBox.setXBounds(minX, maxX) 84 outBox.setYBounds(minY, maxY) 85 return outBox 86 } 87 88 /** 89 * Returns the point on the segment at the given ratio of the segment's length, measured from 90 * the start point. You may also think of this as linearly interpolating from the start of the 91 * segment to the end. Values outside the interval [0, 1] will be extrapolated along the 92 * infinite line passing through this segment. This is the inverse of [project]. 93 * 94 * For performance-sensitive code, prefer to use [computeLerpPoint] with a pre-allocated 95 * instance of [MutableVec]. 96 */ computeLerpPointnull97 public fun computeLerpPoint(ratio: Float): ImmutableVec = 98 ImmutableVec( 99 (1.0f - ratio) * start.x + ratio * end.x, 100 (1.0f - ratio) * start.y + ratio * end.y 101 ) 102 103 /** 104 * Fills [outVec] with the point on the segment at the given ratio of the segment's length, 105 * measured from the start point. You may also think of this as linearly interpolating from the 106 * start of the segment to the end. Values outside the interval [0, 1] will be extrapolated 107 * along the infinite line passing through this segment. This is the inverse of [project]. 108 */ 109 public fun computeLerpPoint(ratio: Float, outVec: MutableVec): MutableVec { 110 outVec.x = (1.0f - ratio) * start.x + ratio * end.x 111 outVec.y = (1.0f - ratio) * start.y + ratio * end.y 112 return outVec 113 } 114 115 /** 116 * Returns the multiple of the segment's length at which the infinite extrapolation of this 117 * segment is closest to [pointToProject]. This is the inverse of [computeLerpPoint]. If the 118 * [computeLength] of this segment is zero, then the projection is undefined and this will throw 119 * an error. Note that the [computeLength] may be zero even if [start] and [end] are not equal, 120 * if they are sufficiently close that floating-point underflow occurs. 121 */ projectnull122 public fun project(pointToProject: Vec): Float { 123 // TODO(b/354236964): Optimize unnecessary allocations 124 if (Vec.areEquivalent(start, end)) { 125 throw IllegalArgumentException("Projecting onto a segment of zero length is undefined.") 126 } 127 // Sometimes start is not exactly equal to the end, but close enough that the 128 // magnitude-squared still is not positive due to floating-point 129 // loss-of-precision. 130 val displacementX = end.x - start.x 131 val displacementY = end.y - start.y 132 val magnitudeSquared = displacementX * displacementX + displacementY * displacementY 133 if (magnitudeSquared <= 0) { 134 throw IllegalArgumentException("Projecting onto a segment of zero length is undefined.") 135 } 136 val scaledDifferenceX = (pointToProject.x - start.x) * displacementX 137 val scaledDifferenceY = (pointToProject.y - start.y) * displacementY 138 return (scaledDifferenceX + scaledDifferenceY) / magnitudeSquared 139 } 140 141 /** 142 * Returns an immutable copy of this object. This will return itself if called on an immutable 143 * instance. 144 */ asImmutablenull145 @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP) public abstract fun asImmutable(): ImmutableSegment 146 147 /** 148 * Compares this [Segment] with [other], and returns true if both [start] points are considered 149 * almost equal with the given [tolerance], and likewise for both [end] points. 150 */ 151 public fun isAlmostEqual(other: Segment, @FloatRange(from = 0.0) tolerance: Float): Boolean = 152 start.isAlmostEqual(other.start, tolerance) && end.isAlmostEqual(other.end, tolerance) 153 154 public companion object { 155 /** 156 * Returns true if [first] and [second] have the same values for all properties of 157 * [Segment]. 158 */ 159 internal fun areEquivalent(first: Segment, second: Segment): Boolean { 160 return Vec.areEquivalent(first.start, second.start) && 161 Vec.areEquivalent(first.end, second.end) 162 } 163 164 /** Returns a hash code for [segment] using its [Segment] properties. */ 165 internal fun hash(segment: Segment): Int = 166 31 * segment.start.hashCode() + segment.end.hashCode() 167 168 /** Returns a string representation for [segment] using its [Segment] properties. */ 169 internal fun string(segment: Segment): String = 170 "Segment(start=${segment.start}, end=${segment.end})" 171 172 /** 173 * Returns the minimum and maximum x and y coordinates for all points inside [segment]. 174 * 175 * This function returns four floats corresponding to the (minX, maxX, minY, maxY) 176 * coordinates of the segment. These coordinates are used to compute the bounding rectangle 177 * of [segment]. 178 */ 179 private fun getBoundingXYCoordinates(segment: Segment) = 180 arrayOf( 181 minOf(segment.start.x, segment.end.x), 182 maxOf(segment.start.x, segment.end.x), 183 minOf(segment.start.y, segment.end.y), 184 maxOf(segment.start.y, segment.end.y), 185 ) 186 } 187 } 188