ModifiedDrawNode.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.node

import androidx.compose.ui.DrawCacheModifier
import androidx.compose.ui.DrawModifier
import androidx.compose.ui.MeasureScope
import androidx.compose.ui.geometry.Size
import androidx.compose.ui.graphics.Canvas
import androidx.compose.ui.unit.toSize

@OptIn(ExperimentalLayoutNodeApi::class)
internal class ModifiedDrawNode(
    wrapped: LayoutNodeWrapper,
    drawModifier: DrawModifier
) : DelegatingLayoutNodeWrapper<DrawModifier>(wrapped, drawModifier), OwnerScope {

    private val cacheDrawModifier: DrawCacheModifier? =
        if (drawModifier is DrawCacheModifier) {
            drawModifier
        } else {
            null
        }

    // Flag to determine if the cache should be re-built
    private var invalidateCache = true

    // Callback used to build the drawing cache
    private val updateCache = {
        val size: Size = measuredSize.toSize()
        cacheDrawModifier?.onBuildCache(size, layoutNode.mDrawScope)
        invalidateCache = false
    }

    override var measureResult: MeasureScope.MeasureResult
        get() = super.measureResult
        set(value) {
            if (super.measuredSize.width != value.width ||
                super.measuredSize.height != value.height
            ) {
                invalidateCache = true
            }
            super.measureResult = value
        }

    // This is not thread safe
    override fun draw(canvas: Canvas) {
        val size = measuredSize.toSize()
        if (cacheDrawModifier != null && invalidateCache) {
            layoutNode.owner?.observeReads(
                this,
                onCommitAffectingModifiedDrawNode,
                updateCache
            )
        }

        val drawScope = layoutNode.mDrawScope
        withPositionTranslation(canvas) {
            drawScope.draw(canvas, size, wrapped) {
                with(drawScope) {
                    with(modifier) {
                        draw()
                    }
                }
            }
        }
    }

    companion object {
        // Callback invoked whenever a state parameter that is read within the cache
        // execution callback is updated. This marks the cache flag as dirty and
        // invalidates the current layer.
        private val onCommitAffectingModifiedDrawNode: (ModifiedDrawNode) -> Unit =
            { modifiedDrawNode ->
                // Note this intentionally does not invalidate the layer as Owner implementations
                // already observe and invalidate the layer on state changes. Instead just
                // mark the cache dirty so that it will be re-created on the next draw
                modifiedDrawNode.invalidateCache = true
            }
    }

    override val isValid: Boolean
        get() = isAttached
}