Add alpha color animation in the beginning of unfold light reveal

Updates linear light reveal which is used in unfold animation
to make it smoother in the beginning by starting the gradient
bounds from non zero width and adding alpha color animation
instead.

Bug: 190818044
Test: manual
Change-Id: If650e4560e7cee70c9414fa20d0a8c1fb90c4970

packages/SystemUI/src/com/android/systemui/statusbar/LightRevealScrim.kt

@@ -12,8 +12,10 @@ import android.graphics.PorterDuffXfermode
 import android.graphics.RadialGradient
 import android.graphics.Shader
 import android.util.AttributeSet
+import android.util.MathUtils.lerp
 import android.view.View
 import com.android.systemui.animation.Interpolators
+import com.android.systemui.statusbar.LightRevealEffect.Companion.getPercentPastThreshold
 import java.util.function.Consumer
 
 /**
@@ -63,12 +65,12 @@ object LiftReveal : LightRevealEffect {
     override fun setRevealAmountOnScrim(amount: Float, scrim: LightRevealScrim) {
         val interpolatedAmount = INTERPOLATOR.getInterpolation(amount)
         val ovalWidthIncreaseAmount =
-                LightRevealEffect.getPercentPastThreshold(interpolatedAmount, WIDEN_OVAL_THRESHOLD)
+                getPercentPastThreshold(interpolatedAmount, WIDEN_OVAL_THRESHOLD)
 
         val initialWidthMultiplier = (1f - OVAL_INITIAL_WIDTH_PERCENT) / 2f
 
         with(scrim) {
-            revealGradientEndColorAlpha = 1f - LightRevealEffect.getPercentPastThreshold(
+            revealGradientEndColorAlpha = 1f - getPercentPastThreshold(
                     amount, FADE_END_COLOR_OUT_THRESHOLD)
             setRevealGradientBounds(
                     scrim.width * initialWidthMultiplier +
@@ -90,26 +92,49 @@ class LinearLightRevealEffect(private val isVertical: Boolean) : LightRevealEffe
     override fun setRevealAmountOnScrim(amount: Float, scrim: LightRevealScrim) {
         val interpolatedAmount = INTERPOLATOR.getInterpolation(amount)
 
-        // TODO(b/193801466): add alpha reveal in the beginning as well
+        scrim.startColorAlpha =
+            getPercentPastThreshold(1 - interpolatedAmount,
+                threshold = 1 - START_COLOR_REVEAL_PERCENTAGE)
+
         scrim.revealGradientEndColorAlpha =
-            1f - LightRevealEffect.getPercentPastThreshold(interpolatedAmount, threshold = 0.6f)
+            1f - getPercentPastThreshold(interpolatedAmount,
+                threshold = REVEAL_GRADIENT_END_COLOR_ALPHA_START_PERCENTAGE)
+
+        // Start changing gradient bounds later to avoid harsh gradient in the beginning
+        val gradientBoundsAmount = lerp(GRADIENT_START_BOUNDS_PERCENTAGE, 1.0f, interpolatedAmount)
 
         if (isVertical) {
             scrim.setRevealGradientBounds(
-                left = scrim.width / 2 - (scrim.width / 2) * interpolatedAmount,
+                left = scrim.width / 2 - (scrim.width / 2) * gradientBoundsAmount,
                 top = 0f,
-                right = scrim.width / 2 + (scrim.width / 2) * interpolatedAmount,
+                right = scrim.width / 2 + (scrim.width / 2) * gradientBoundsAmount,
                 bottom = scrim.height.toFloat()
             )
         } else {
             scrim.setRevealGradientBounds(
                 left = 0f,
-                top = scrim.height / 2 - (scrim.height / 2) * interpolatedAmount,
+                top = scrim.height / 2 - (scrim.height / 2) * gradientBoundsAmount,
                 right = scrim.width.toFloat(),
-                bottom = scrim.height / 2 + (scrim.height / 2) * interpolatedAmount
+                bottom = scrim.height / 2 + (scrim.height / 2) * gradientBoundsAmount
             )
         }
     }
+
+    private companion object {
+        // From which percentage we should start the gradient reveal width
+        // E.g. if 0 - starts with 0px width, 0.3f - starts with 30% width
+        private const val GRADIENT_START_BOUNDS_PERCENTAGE = 0.3f
+
+        // When to start changing alpha color of the gradient scrim
+        // E.g. if 0.6f - starts fading the gradient away at 60% and becomes completely
+        // transparent at 100%
+        private const val REVEAL_GRADIENT_END_COLOR_ALPHA_START_PERCENTAGE = 0.6f
+
+        // When to finish displaying start color fill that reveals the content
+        // E.g. if 0.3f - the content won't be visible at 0% and it will gradually
+        // reduce the alpha until 30% (at this point the color fill is invisible)
+        private const val START_COLOR_REVEAL_PERCENTAGE = 0.3f
+    }
 }
 
 class CircleReveal(
@@ -125,7 +150,7 @@ class CircleReveal(
     override fun setRevealAmountOnScrim(amount: Float, scrim: LightRevealScrim) {
         // reveal amount updates already have an interpolator, so we intentionally use the
         // non-interpolated amount
-        val fadeAmount = LightRevealEffect.getPercentPastThreshold(amount, 0.5f)
+        val fadeAmount = getPercentPastThreshold(amount, 0.5f)
         val radius = startRadius + ((endRadius - startRadius) * amount)
         scrim.revealGradientEndColorAlpha = 1f - fadeAmount
         scrim.setRevealGradientBounds(
@@ -153,8 +178,7 @@ class PowerButtonReveal(
 
     override fun setRevealAmountOnScrim(amount: Float, scrim: LightRevealScrim) {
         val interpolatedAmount = Interpolators.FAST_OUT_SLOW_IN_REVERSE.getInterpolation(amount)
-        val fadeAmount =
-                LightRevealEffect.getPercentPastThreshold(interpolatedAmount, 0.5f)
+        val fadeAmount = getPercentPastThreshold(interpolatedAmount, 0.5f)
 
         with(scrim) {
             revealGradientEndColorAlpha = 1f - fadeAmount
@@ -213,6 +237,23 @@ class LightRevealScrim(context: Context?, attrs: AttributeSet?) : View(context,
     var revealGradientWidth: Float = 0f
     var revealGradientHeight: Float = 0f
 
+    /**
+     * Alpha of the fill that can be used in the beginning of the animation to hide the content.
+     * Normally the gradient bounds are animated from small size so the content is not visible,
+     * but if the start gradient bounds allow to see some content this could be used to make the
+     * reveal smoother. It can help to add fade in effect in the beginning of the animation.
+     * The color of the fill is determined by [revealGradientEndColor].
+     *
+     * 0 - no fill and content is visible, 1 - the content is covered with the start color
+     */
+    var startColorAlpha = 0f
+        set(value) {
+            if (field != value) {
+                field = value
+                invalidate()
+            }
+        }
+
     var revealGradientEndColor: Int = Color.BLACK
         set(value) {
             if (field != value) {
@@ -281,6 +322,10 @@ class LightRevealScrim(context: Context?, attrs: AttributeSet?) : View(context,
             return
         }
 
+        if (startColorAlpha > 0f) {
+            canvas.drawColor(updateColorAlpha(revealGradientEndColor, startColorAlpha))
+        }
+
         with(shaderGradientMatrix) {
             setScale(revealGradientWidth, revealGradientHeight, 0f, 0f)
             postTranslate(revealGradientCenter.x, revealGradientCenter.y)
@@ -294,11 +339,15 @@ class LightRevealScrim(context: Context?, attrs: AttributeSet?) : View(context,
 
     private fun setPaintColorFilter() {
         gradientPaint.colorFilter = PorterDuffColorFilter(
-                Color.argb(
-                        (revealGradientEndColorAlpha * 255).toInt(),
-                        Color.red(revealGradientEndColor),
-                        Color.green(revealGradientEndColor),
-                        Color.blue(revealGradientEndColor)),
-                PorterDuff.Mode.MULTIPLY)
+            updateColorAlpha(revealGradientEndColor, revealGradientEndColorAlpha),
+            PorterDuff.Mode.MULTIPLY)
     }
+
+    private fun updateColorAlpha(color: Int, alpha: Float): Int =
+        Color.argb(
+            (alpha * 255).toInt(),
+            Color.red(color),
+            Color.green(color),
+            Color.blue(color)
+        )
 }