TextFieldCursor.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.foundation.text

import androidx.compose.animation.core.Animatable
import androidx.compose.animation.core.AnimationSpec
import androidx.compose.animation.core.infiniteRepeatable
import androidx.compose.animation.core.keyframes
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.composed
import androidx.compose.ui.draw.drawWithContent
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.geometry.Rect
import androidx.compose.ui.graphics.Brush
import androidx.compose.ui.graphics.SolidColor
import androidx.compose.ui.graphics.isUnspecified
import androidx.compose.ui.text.input.OffsetMapping
import androidx.compose.ui.text.input.TextFieldValue
import androidx.compose.ui.unit.dp

@Suppress("ModifierInspectorInfo")
internal fun Modifier.cursor(
    state: TextFieldState,
    value: TextFieldValue,
    offsetMapping: OffsetMapping,
    cursorBrush: Brush,
    enabled: Boolean
) = if (enabled) composed {
    val cursorAlpha = remember { Animatable(1f) }
    val isBrushSpecified = !(cursorBrush is SolidColor && cursorBrush.value.isUnspecified)
    if (state.hasFocus && value.selection.collapsed && isBrushSpecified) {
        LaunchedEffect(value.annotatedString, value.selection) {
            // ensure that the value is always 1f _this_ frame by calling snapTo
            cursorAlpha.snapTo(1f)
            // then start the cursor blinking on animation clock (500ms on to start)
            cursorAlpha.animateTo(0f, cursorAnimationSpec)
        }
        drawWithContent {
            this.drawContent()
            val cursorAlphaValue = cursorAlpha.value.coerceIn(0f, 1f)
            if (cursorAlphaValue != 0f) {
                val transformedOffset = offsetMapping
                    .originalToTransformed(value.selection.start)
                val cursorRect = state.layoutResult?.value?.getCursorRect(transformedOffset)
                    ?: Rect(0f, 0f, 0f, 0f)
                val cursorWidth = DefaultCursorThickness.toPx()
                val cursorX = (cursorRect.left + cursorWidth / 2)
                    .coerceAtMost(size.width - cursorWidth / 2)

                drawLine(
                    cursorBrush,
                    Offset(cursorX, cursorRect.top),
                    Offset(cursorX, cursorRect.bottom),
                    alpha = cursorAlphaValue,
                    strokeWidth = cursorWidth
                )
            }
        }
    } else {
        Modifier
    }
} else this

private val cursorAnimationSpec: AnimationSpec<Float> = infiniteRepeatable(
    animation = keyframes {
        durationMillis = 1000
        1f at 0
        1f at 499
        0f at 500
        0f at 999
    }
)

internal val DefaultCursorThickness = 2.dp