Non-stretching Glide placeholder

PaddingTransition.kt

import android.graphics.drawable.Drawable
import com.bumptech.glide.request.transition.Transition

class PaddingTransition<T : Drawable>(private val realTransition: Transition<in T>) : Transition<T> {

    override fun transition(current: T, adapter: Transition.ViewAdapter): Boolean {
        val width = current.intrinsicWidth
        val height = current.intrinsicHeight
        return realTransition.transition(current, PaddingViewAdapter(adapter, width, height))
    }
}

PaddingTransitionFactory.kt

import android.graphics.drawable.Drawable

import com.bumptech.glide.load.DataSource
import com.bumptech.glide.request.transition.DrawableCrossFadeFactory
import com.bumptech.glide.request.transition.Transition
import com.bumptech.glide.request.transition.TransitionFactory

class PaddingTransitionFactory<T : Drawable>(
        private val realFactory: DrawableCrossFadeFactory
) : TransitionFactory<T> {

    override fun build(dataSource: DataSource, b: Boolean): Transition<T> {
        return PaddingTransition(realFactory.build(dataSource, b))
    }
}

PaddingViewAdapter.kt

import android.graphics.drawable.Drawable
import android.graphics.drawable.InsetDrawable
import android.graphics.drawable.TransitionDrawable
import android.os.Build
import android.view.View

class PaddingViewAdapter(
        private val realAdapter: Transition.ViewAdapter,
        private val targetWidth: Int,
        private val targetHeight: Int) : Transition.ViewAdapter {

    override fun getView(): View = realAdapter.view

    override fun getCurrentDrawable(): Drawable? {
        var drawable = realAdapter.currentDrawable
        if (drawable != null) {
            val padX = Math.max(0, targetWidth - drawable.intrinsicWidth) / 2
            val padY = Math.max(0, targetHeight - drawable.intrinsicHeight) / 2
            if (padX > 0 || padY > 0) {
                drawable = InsetDrawable(drawable, padX, padY, padX, padY)
            }
        }
        return drawable
    }

    override fun setDrawable(drawable: Drawable) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && drawable is TransitionDrawable) {
            // For some reason padding is taken into account differently on M than before in LayerDrawable
            // PaddingMode was introduced in 21 and gravity in 23, I think NO_GRAVITY default may play
            // a role in this, but didn't have time to dig deeper than this.
            drawable.paddingMode = TransitionDrawable.PADDING_MODE_STACK
        }
        realAdapter.setDrawable(drawable)
    }
}

usage.kt

val transitionFactory = DrawableCrossFadeFactory.Builder()
            .setCrossFadeEnabled(true)
            .build()

val placeholder = R.drawable.ic_placeholder_white_24dp

// The default Glide behavior is to stretch the placeholder to fit the ImageView
// This makes the placeholder be exactly its intrinsic size - 24dp in this example.
Glide.with(acitivity)
      .load(imageUrl)
      .apply(RequestOptions()
              .diskCacheStrategy(DiskCacheStrategy.ALL)
              .placeholder(placeholder)
              .fitCenter())
      .transition(DrawableTransitionOptions.with(PaddingTransitionFactory(transitionFactory)))
      .into(imageView)