画像を文字のascentとbaselineの中央に配置するImageSpan

CenteredImageSpan.kt

class CenteredImageSpan(
        context: Context,
        resourceId: Int
) : ImageSpan(context, resourceId) {
    private val drawableRef = AtomicReference<Drawable?>()

    private val cachedDrawable: Drawable
        get() = drawableRef.get() ?: drawable.apply {
            drawableRef.set(drawable)
        }

    override fun draw(
            canvas: Canvas,
            text: CharSequence?,
            start: Int,
            end: Int,
            x: Float,
            top: Int,
            y: Int,
            bottom: Int,
            paint: Paint
    ) {
        val d = cachedDrawable
        canvas.save()
        val fontAscent = paint.fontMetricsInt.ascent
        val transY = y + fontAscent - (d.intrinsicHeight + fontAscent) / 2f
        canvas.translate(x, transY)
        d.draw(canvas)
        canvas.restore()
    }

    override fun getSize(
            paint: Paint,
            text: CharSequence?,
            start: Int,
            end: Int,
            fm: Paint.FontMetricsInt?
    ): Int {
        val d = cachedDrawable
        val rect = d.bounds

        if (fm != null) {
            val pfm = paint.fontMetricsInt
            fm.ascent = pfm.ascent
            fm.descent = pfm.descent
            fm.top = pfm.top
            fm.bottom = pfm.bottom
        }

        return rect.right
    }
}