TextIndent.kt

/*
 * Copyright 2019 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package androidx.compose.ui.text.style

import androidx.compose.runtime.Immutable
import androidx.compose.runtime.Stable
import androidx.compose.ui.text.lerpTextUnitInheritable
import androidx.compose.ui.unit.TextUnit
import androidx.compose.ui.unit.sp

/**
 * Specify the indentation of a paragraph.
 *
 * @param firstLine the amount of indentation applied to the first line.
 * @param restLine the amount of indentation applied to every line except the first line.
 */
@Immutable
data class TextIndent(
    val firstLine: TextUnit = 0.sp,
    val restLine: TextUnit = 0.sp
) {
    companion object {
        /**
         * Constant fot no text indent.
         */
        @Stable
        val None = TextIndent()
    }
}

/**
 * Linearly interpolate between two [TextIndent]s.
 *
 * The [fraction] argument represents position on the timeline, with 0.0 meaning
 * that the interpolation has not started, returning [start] (or something
 * equivalent to [start]), 1.0 meaning that the interpolation has finished,
 * returning [stop] (or something equivalent to [stop]), and values in between
 * meaning that the interpolation is at the relevant point on the timeline
 * between [start] and [stop]. The interpolation can be extrapolated beyond 0.0 and
 * 1.0, so negative values and values greater than 1.0 are valid.
 */
fun lerp(start: TextIndent, stop: TextIndent, fraction: Float): TextIndent {
    return TextIndent(
        lerpTextUnitInheritable(start.firstLine, stop.firstLine, fraction),
        lerpTextUnitInheritable(start.restLine, stop.restLine, fraction)
    )
}