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Commit c74e9ff4 authored by Jordan Demeulenaere's avatar Jordan Demeulenaere
Browse files

Force new fading elements to fade from 0 alpha 

This CL makes sure that new elements that were never drawn in any scene
and that appear by fading always start at alpha = 0f. This ensures that
elements never appear instantly even if the transition making them
appear on screen start at progress >> 0f.

Bug: 290930950
Test: ElementTest
Flag: com.android.systemui.scene_container
Change-Id: I7e5f70fd9657d5b8c2dd29881828b973a7ac1e4d
parent b49ba446

packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/Element.kt

+11 −0
Original line number Diff line number Diff line
@@ -66,6 +66,9 @@ internal class Element(val key: ElementKey) { 
     */

    var lastTransition: TransitionState.Transition? = null



    /** Whether this element was ever drawn in a scene. */

    var wasDrawnInAnyScene = false



    override fun toString(): String {

        return "Element(key=$key)"

    }
@@ -389,6 +392,8 @@ internal class ElementNode( 
    }



    override fun ContentDrawScope.draw() {

        element.wasDrawnInAnyScene = true



        val transition = elementTransition(element, currentTransitions)

        val drawScale = getDrawScale(layoutImpl, scene, element, transition, sceneState)

        if (drawScale == Scale.Default) {
@@ -726,6 +731,12 @@ private fun elementAlpha( 
            )

            .fastCoerceIn(0f, 1f)



    // If the element is fading during this transition and that it is drawn for the first time, make

    // sure that it doesn't instantly appear on screen.

    if (!element.wasDrawnInAnyScene && alpha > 0f) {

        element.sceneStates.forEach { it.value.alphaBeforeInterruption = 0f }

    }



    val interruptedAlpha = interruptedAlpha(layoutImpl, transition, sceneState, alpha)

    sceneState.lastAlpha = interruptedAlpha

    return interruptedAlpha

packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/ElementTest.kt

+48 −0
Original line number Diff line number Diff line
@@ -1481,4 +1481,52 @@ class ElementTest { 
        assertThat(fooInC.lastAlpha).isEqualTo(1f)

        assertThat(fooInB.lastAlpha).isEqualTo(Element.AlphaUnspecified)

    }



    @Test

    fun fadingElementsDontAppearInstantly() {

        val state =

            rule.runOnUiThread {

                MutableSceneTransitionLayoutStateImpl(

                    SceneA,

                    transitions { from(SceneA, to = SceneB) { fade(TestElements.Foo) } }

                )

            }



        lateinit var layoutImpl: SceneTransitionLayoutImpl

        rule.setContent {

            SceneTransitionLayoutForTesting(state, onLayoutImpl = { layoutImpl = it }) {

                scene(SceneA) {}

                scene(SceneB) { Box(Modifier.element(TestElements.Foo)) }

            }

        }



        // Start A => B at 60%.

        var interruptionProgress by mutableStateOf(1f)

        rule.runOnUiThread {

            state.startTransition(

                transition(

                    from = SceneA,

                    to = SceneB,

                    progress = { 0.6f },

                    interruptionProgress = { interruptionProgress },

                ),

                transitionKey = null

            )

        }

        rule.waitForIdle()



        // Alpha of Foo should be 0f at interruption progress 100%.

        val fooInB = layoutImpl.elements.getValue(TestElements.Foo).sceneStates.getValue(SceneB)

        assertThat(fooInB.lastAlpha).isEqualTo(0f)



        // Alpha of Foo should be 0.6f at interruption progress 0%.

        interruptionProgress = 0f

        rule.waitForIdle()

        assertThat(fooInB.lastAlpha).isEqualTo(0.6f)



        // Alpha of Foo should be 0.3f at interruption progress 50%.

        interruptionProgress = 0.5f

        rule.waitForIdle()

        assertThat(fooInB.lastAlpha).isEqualTo(0.3f)

    }

}