commonMain.androidx.compose.foundation.text.modifiers.MinLinesConstrainer.kt Maven / Gradle / Ivy

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Higher level abstractions of the Compose UI primitives. This library is design system agnostic, providing the high-level building blocks for both application and design-system developers
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/*
 * Copyright 2023 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.foundation.text.modifiers

import androidx.compose.ui.text.Paragraph
import androidx.compose.ui.text.TextStyle
import androidx.compose.ui.text.font.FontFamily
import androidx.compose.ui.text.resolveDefaults
import androidx.compose.ui.text.style.TextOverflow
import androidx.compose.ui.unit.Constraints
import androidx.compose.ui.unit.Density
import androidx.compose.ui.unit.LayoutDirection
import androidx.compose.ui.util.fastRoundToInt

/**
 * Coerce min and max lines into actual constraints.
 *
 * Results are cached with the assumption that there is typically N=1 style being coerced at once.
 */
internal class MinLinesConstrainer
private constructor(
    val layoutDirection: LayoutDirection,
    val inputTextStyle: TextStyle,
    val density: Density,
    val fontFamilyResolver: FontFamily.Resolver
) {
    private val resolvedStyle = resolveDefaults(inputTextStyle, layoutDirection)
    private var lineHeightCache: Float = Float.NaN
    private var oneLineHeightCache: Float = Float.NaN

    companion object {
        // LRU cache of one since this tends to be used for similar styles
        // ... it may be useful to increase this cache if requested by some dev use case
        private var last: MinLinesConstrainer? = null

        /** Returns a coercer (possibly cached) with these parameters */
        fun from(
            minMaxUtil: MinLinesConstrainer?,
            layoutDirection: LayoutDirection,
            paramStyle: TextStyle,
            density: Density,
            fontFamilyResolver: FontFamily.Resolver
        ): MinLinesConstrainer {
            minMaxUtil?.let {
                if (
                    layoutDirection == it.layoutDirection &&
                        paramStyle == it.inputTextStyle &&
                        density.density == it.density.density &&
                        fontFamilyResolver === it.fontFamilyResolver
                ) {
                    return it
                }
            }
            last?.let {
                if (
                    layoutDirection == it.layoutDirection &&
                        paramStyle == it.inputTextStyle &&
                        density.density == it.density.density &&
                        fontFamilyResolver === it.fontFamilyResolver
                ) {
                    return it
                }
            }
            return MinLinesConstrainer(
                    layoutDirection,
                    resolveDefaults(paramStyle, layoutDirection),
                    // other density implementations may hold references to views/activities
                    // which the cache outlives, potentially causing memory leak.
                    Density(density.density, density.fontScale),
                    fontFamilyResolver
                )
                .also { last = it }
        }
    }

    /**
     * Coerce inConstraints to have min and max lines applied.
     *
     * On first invocation this will cause (2) Paragraph measurements.
     */
    internal fun coerceMinLines(inConstraints: Constraints, minLines: Int): Constraints {
        var oneLineHeight = oneLineHeightCache
        var lineHeight = lineHeightCache
        if (oneLineHeight.isNaN() || lineHeight.isNaN()) {
            oneLineHeight =
                Paragraph(
                        text = EmptyTextReplacement,
                        style = resolvedStyle,
                        constraints = Constraints(),
                        density = density,
                        fontFamilyResolver = fontFamilyResolver,
                        maxLines = 1,
                        overflow = TextOverflow.Clip
                    )
                    .height

            val twoLineHeight =
                Paragraph(
                        text = TwoLineTextReplacement,
                        style = resolvedStyle,
                        constraints = Constraints(),
                        density = density,
                        fontFamilyResolver = fontFamilyResolver,
                        maxLines = 2,
                        overflow = TextOverflow.Clip
                    )
                    .height

            lineHeight = twoLineHeight - oneLineHeight
            oneLineHeightCache = oneLineHeight
            lineHeightCache = lineHeight
        }
        val minHeight =
            if (minLines != 1) {
                (oneLineHeight + (lineHeight * (minLines - 1)))
                    .fastRoundToInt()
                    .coerceAtLeast(0)
                    .coerceAtMost(inConstraints.maxHeight)
            } else {
                inConstraints.minHeight
            }
        return Constraints(
            minHeight = minHeight,
            maxHeight = inConstraints.maxHeight,
            minWidth = inConstraints.minWidth,
            maxWidth = inConstraints.maxWidth,
        )
    }
}

private const val DefaultWidthCharCount = 10 // min width for TextField is 10 chars long
private val EmptyTextReplacement = "H".repeat(DefaultWidthCharCount) // just a reference character.
private val TwoLineTextReplacement = EmptyTextReplacement + "\n" + EmptyTextReplacement