ShaderBrushSpan.android.kt
/*
* Copyright 2022 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.platform.style
import android.graphics.Shader
import android.text.TextPaint
import android.text.style.CharacterStyle
import android.text.style.UpdateAppearance
import androidx.compose.ui.geometry.Size
import androidx.compose.ui.geometry.isUnspecified
import androidx.compose.ui.graphics.ShaderBrush
import androidx.compose.ui.text.platform.setAlpha
/**
* A span that applies [ShaderBrush] to TextPaint after receiving a specified size
*/
internal class ShaderBrushSpan(
val shaderBrush: ShaderBrush,
val alpha: Float
) : CharacterStyle(), UpdateAppearance {
var size: Size = Size.Unspecified
private var cachedShader: Pair<Size, Shader>? = null
override fun updateDrawState(textPaint: TextPaint) {
textPaint.setAlpha(alpha)
if (size.isUnspecified) return
val finalCachedShader = cachedShader
val shader = if (finalCachedShader == null || finalCachedShader.first != size) {
// if cached shader is not initialized or the size has changed, recreate the shader
shaderBrush.createShader(size)
} else {
// reuse the earlier created shader
finalCachedShader.second
}
textPaint.shader = shader
cachedShader = size to shader
}
}