xref: /compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/layout/LayoutModifier.kt

/*
 * Copyright 2020 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.layout

import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.GraphicsLayerScope
import androidx.compose.ui.internal.JvmDefaultWithCompatibility
import androidx.compose.ui.node.LayoutModifierNode
import androidx.compose.ui.node.ModifierNodeElement
import androidx.compose.ui.platform.InspectorInfo
import androidx.compose.ui.unit.Constraints
import androidx.compose.ui.unit.IntOffset
import androidx.compose.ui.unit.IntSize

/**
 * A [Modifier.Element] that changes how its wrapped content is measured and laid out. It has the
 * same measurement and layout functionality as the [androidx.compose.ui.layout.Layout] component,
 * while wrapping exactly one layout due to it being a modifier. In contrast, the
 * [androidx.compose.ui.layout.Layout] component is used to define the layout behavior of multiple
 * children.
 *
 * @sample androidx.compose.ui.samples.LayoutModifierSample
 * @see androidx.compose.ui.layout.Layout
 */
@JvmDefaultWithCompatibility
interface LayoutModifier : Modifier.Element {
    /**
     * The function used to measure the modifier. The [measurable] corresponds to the wrapped
     * content, and it can be measured with the desired constraints according to the logic of the
     * [LayoutModifier]. The modifier needs to choose its own size, which can depend on the size
     * chosen by the wrapped content (the obtained [Placeable]), if the wrapped content was
     * measured. The size needs to be returned as part of a [MeasureResult], alongside the placement
     * logic of the [Placeable], which defines how the wrapped content should be positioned inside
     * the [LayoutModifier]. A convenient way to create the [MeasureResult] is to use the
     * [MeasureScope.layout] factory function.
     *
     * A [LayoutModifier] uses the same measurement and layout concepts and principles as a
     * [Layout], the only difference is that they apply to exactly one child. For a more detailed
     * explanation of measurement and layout, see [MeasurePolicy].
     */
    fun MeasureScope.measure(measurable: Measurable, constraints: Constraints): MeasureResult

    /** The function used to calculate [IntrinsicMeasurable.minIntrinsicWidth]. */
    fun IntrinsicMeasureScope.minIntrinsicWidth(measurable: IntrinsicMeasurable, height: Int): Int =
        MeasuringIntrinsics.minWidth(this@LayoutModifier, this, measurable, height)

    /** The lambda used to calculate [IntrinsicMeasurable.minIntrinsicHeight]. */
    fun IntrinsicMeasureScope.minIntrinsicHeight(measurable: IntrinsicMeasurable, width: Int): Int =
        MeasuringIntrinsics.minHeight(this@LayoutModifier, this, measurable, width)

    /** The function used to calculate [IntrinsicMeasurable.maxIntrinsicWidth]. */
    fun IntrinsicMeasureScope.maxIntrinsicWidth(measurable: IntrinsicMeasurable, height: Int): Int =
        MeasuringIntrinsics.maxWidth(this@LayoutModifier, this, measurable, height)

    /** The lambda used to calculate [IntrinsicMeasurable.maxIntrinsicHeight]. */
    fun IntrinsicMeasureScope.maxIntrinsicHeight(measurable: IntrinsicMeasurable, width: Int): Int =
        MeasuringIntrinsics.maxHeight(this@LayoutModifier, this, measurable, width)
}

// TODO(popam): deduplicate from the copy-pasted logic of Layout.kt without making it public
private object MeasuringIntrinsics {
    fun minWidth(
        modifier: LayoutModifier,
        intrinsicMeasureScope: IntrinsicMeasureScope,
        intrinsicMeasurable: IntrinsicMeasurable,
        h: Int
    ): Int {
        val measurable =
            DefaultIntrinsicMeasurable(
                intrinsicMeasurable,
                IntrinsicMinMax.Min,
                IntrinsicWidthHeight.Width
            )
        val constraints = Constraints(maxHeight = h)
        val layoutResult =
            with(modifier) {
                IntrinsicsMeasureScope(intrinsicMeasureScope, intrinsicMeasureScope.layoutDirection)
                    .measure(measurable, constraints)
            }
        return layoutResult.width
    }

    fun minHeight(
        modifier: LayoutModifier,
        intrinsicMeasureScope: IntrinsicMeasureScope,
        intrinsicMeasurable: IntrinsicMeasurable,
        w: Int
    ): Int {
        val measurable =
            DefaultIntrinsicMeasurable(
                intrinsicMeasurable,
                IntrinsicMinMax.Min,
                IntrinsicWidthHeight.Height
            )
        val constraints = Constraints(maxWidth = w)
        val layoutResult =
            with(modifier) {
                IntrinsicsMeasureScope(intrinsicMeasureScope, intrinsicMeasureScope.layoutDirection)
                    .measure(measurable, constraints)
            }
        return layoutResult.height
    }

    fun maxWidth(
        modifier: LayoutModifier,
        intrinsicMeasureScope: IntrinsicMeasureScope,
        intrinsicMeasurable: IntrinsicMeasurable,
        h: Int
    ): Int {
        val measurable =
            DefaultIntrinsicMeasurable(
                intrinsicMeasurable,
                IntrinsicMinMax.Max,
                IntrinsicWidthHeight.Width
            )
        val constraints = Constraints(maxHeight = h)
        val layoutResult =
            with(modifier) {
                IntrinsicsMeasureScope(intrinsicMeasureScope, intrinsicMeasureScope.layoutDirection)
                    .measure(measurable, constraints)
            }
        return layoutResult.width
    }

    fun maxHeight(
        modifier: LayoutModifier,
        intrinsicMeasureScope: IntrinsicMeasureScope,
        intrinsicMeasurable: IntrinsicMeasurable,
        w: Int
    ): Int {
        val measurable =
            DefaultIntrinsicMeasurable(
                intrinsicMeasurable,
                IntrinsicMinMax.Max,
                IntrinsicWidthHeight.Height
            )
        val constraints = Constraints(maxWidth = w)
        val layoutResult =
            with(modifier) {
                IntrinsicsMeasureScope(intrinsicMeasureScope, intrinsicMeasureScope.layoutDirection)
                    .measure(measurable, constraints)
            }
        return layoutResult.height
    }

    private class DefaultIntrinsicMeasurable(
        val measurable: IntrinsicMeasurable,
        val minMax: IntrinsicMinMax,
        val widthHeight: IntrinsicWidthHeight
    ) : Measurable {
        override val parentData: Any?
            get() = measurable.parentData

        override fun measure(constraints: Constraints): Placeable {
            if (widthHeight == IntrinsicWidthHeight.Width) {
                val width =
                    if (minMax == IntrinsicMinMax.Max) {
                        measurable.maxIntrinsicWidth(constraints.maxHeight)
                    } else {
                        measurable.minIntrinsicWidth(constraints.maxHeight)
                    }
                val height =
                    if (constraints.hasBoundedHeight) constraints.maxHeight else LargeDimension
                return EmptyPlaceable(width, height)
            }
            val height =
                if (minMax == IntrinsicMinMax.Max) {
                    measurable.maxIntrinsicHeight(constraints.maxWidth)
                } else {
                    measurable.minIntrinsicHeight(constraints.maxWidth)
                }
            val width = if (constraints.hasBoundedWidth) constraints.maxWidth else LargeDimension
            return EmptyPlaceable(width, height)
        }

        override fun minIntrinsicWidth(height: Int): Int {
            return measurable.minIntrinsicWidth(height)
        }

        override fun maxIntrinsicWidth(height: Int): Int {
            return measurable.maxIntrinsicWidth(height)
        }

        override fun minIntrinsicHeight(width: Int): Int {
            return measurable.minIntrinsicHeight(width)
        }

        override fun maxIntrinsicHeight(width: Int): Int {
            return measurable.maxIntrinsicHeight(width)
        }
    }

    private class EmptyPlaceable(width: Int, height: Int) : Placeable() {
        init {
            measuredSize = IntSize(width, height)
        }

        override fun get(alignmentLine: AlignmentLine): Int = AlignmentLine.Unspecified

        override fun placeAt(
            position: IntOffset,
            zIndex: Float,
            layerBlock: (GraphicsLayerScope.() -> Unit)?
        ) {}
    }

    private enum class IntrinsicMinMax {
        Min,
        Max
    }

    private enum class IntrinsicWidthHeight {
        Width,
        Height
    }
}

/**
 * Creates a [LayoutModifier] that allows changing how the wrapped element is measured and laid out.
 *
 * This is a convenience API of creating a custom [LayoutModifier] modifier, without having to
 * create a class or an object that implements the [LayoutModifier] interface. The intrinsic
 * measurements follow the default logic provided by the [LayoutModifier].
 *
 * Example usage:
 *
 * @sample androidx.compose.ui.samples.ConvenienceLayoutModifierSample
 * @see androidx.compose.ui.layout.LayoutModifier
 */
fun Modifier.layout(measure: MeasureScope.(Measurable, Constraints) -> MeasureResult) =
    this then LayoutElement(measure)

private class LayoutElement(val measure: MeasureScope.(Measurable, Constraints) -> MeasureResult) :
    ModifierNodeElement<LayoutModifierImpl>() {
    override fun create() = LayoutModifierImpl(measure)

    override fun update(node: LayoutModifierImpl) {
        node.measureBlock = measure
    }

    override fun InspectorInfo.inspectableProperties() {
        name = "layout"
        properties["measure"] = measure
    }

    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other !is LayoutElement) return false

        if (measure !== other.measure) return false

        return true
    }

    override fun hashCode(): Int {
        return measure.hashCode()
    }
}

internal class LayoutModifierImpl(
    var measureBlock: MeasureScope.(Measurable, Constraints) -> MeasureResult
) : LayoutModifierNode, Modifier.Node() {
    override fun MeasureScope.measure(measurable: Measurable, constraints: Constraints) =
        measureBlock(measurable, constraints)

    override fun toString(): String {
        return "LayoutModifierImpl(measureBlock=$measureBlock)"
    }
}