[resources] Update resource filtering and add density-based lookup

The ResourceEnvironment class has been updated to include a filter by density. Now, resources are selected based on the screen size qualifiers, with the system defaulting to resources designed for a smaller screen if there are no better matches. Corresponding methods have also been enhanced and a test for image resource density has been added to verify the implemented changes.
JetBrains · Jun 14, 2024 · bffc4b7 · bffc4b7
1 parent a1b88db
commit bffc4b7
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diff --git a/...rces/library/src/commonMain/kotlin/org/jetbrains/compose/resources/ResourceEnvironment.kt b/...rces/library/src/commonMain/kotlin/org/jetbrains/compose/resources/ResourceEnvironment.kt
@@ -97,7 +97,7 @@ internal fun Resource.getResourceItemByEnvironment(environment: ResourceEnvironm
         .also { if (it.size == 1) return it.first() }
         .filterBy(environment.theme)
         .also { if (it.size == 1) return it.first() }
-        .filterBy(environment.density)
+        .filterByDensity(environment.density)
         .also { if (it.size == 1) return it.first() }
         .let { items ->
             if (items.isEmpty()) {
@@ -125,12 +125,40 @@ private fun List<ResourceItem>.filterBy(qualifier: Qualifier): List<ResourceItem
     }
 }
 
+// https://developer.android.com/guide/topics/resources/providing-resources#BestMatch
+// When selecting resources based on the screen size qualifiers,
+// the system uses resources designed for a screen smaller than the current screen
+// if there are no resources that better match.
+// For example, a large-size screen uses normal-size screen resources if necessary.
+private fun List<ResourceItem>.filterByDensity(density: DensityQualifier): List<ResourceItem> {
+    val items = this
+
+    val qualifiers = DensityQualifier.entries
+        .filter { it.dpi <= density.dpi }
+        .sortedByDescending { it.dpi }
+
+    var withQualifier = emptyList<ResourceItem>()
+    for (qualifier in qualifiers) {
+        withQualifier = items.filter { item -> item.qualifiers.any { it == qualifier } }
+        if (withQualifier.isNotEmpty()) break
+    }
+    if (withQualifier.isNotEmpty()) return withQualifier
+
+    //items with no DensityQualifier (default)
+    return items.filter { item ->
+        item.qualifiers.none { it is DensityQualifier }
+    }
+}
+
 // we need to filter by language and region together because there is slightly different logic:
 // 1) if there is the exact match language+region then use it
 // 2) if there is the language WITHOUT region match then use it
 // 3) in other cases use items WITHOUT language and region qualifiers at all
 // issue: https://github.com/JetBrains/compose-multiplatform/issues/4571
-private fun List<ResourceItem>.filterByLocale(language: LanguageQualifier, region: RegionQualifier): List<ResourceItem> {
+private fun List<ResourceItem>.filterByLocale(
+    language: LanguageQualifier,
+    region: RegionQualifier
+): List<ResourceItem> {
     val withLanguage = filter { item ->
         item.qualifiers.any { it == language }
     }

diff --git a/...rces/library/src/commonTest/kotlin/org/jetbrains/compose/resources/ComposeResourceTest.kt b/...rces/library/src/commonTest/kotlin/org/jetbrains/compose/resources/ComposeResourceTest.kt
@@ -59,6 +59,44 @@ class ComposeResourceTest {
         )
     }
 
+    @Test
+    fun testImageResourceDensity() = runComposeUiTest {
+        val testResourceReader = TestResourceReader()
+        val imgRes = DrawableResource(
+            "test_id", setOf(
+                ResourceItem(setOf(DensityQualifier.MDPI), "2.png", -1, -1), //MDPI
+                ResourceItem(emptySet(), "1.png", -1, -1), //Default
+            )
+        )
+        val lowDpiEnvironment = object : ComposeEnvironment {
+            @Composable
+            override fun rememberEnvironment() = ResourceEnvironment(
+                language = LanguageQualifier("en"),
+                region = RegionQualifier("US"),
+                theme = ThemeQualifier.LIGHT,
+                density = DensityQualifier.LDPI
+            )
+        }
+
+        var environment by mutableStateOf(TestComposeEnvironment)
+        setContent {
+            CompositionLocalProvider(
+                LocalResourceReader provides testResourceReader,
+                LocalComposeEnvironment provides environment
+            ) {
+                Image(painterResource(imgRes), null)
+            }
+        }
+        waitForIdle()
+        environment = lowDpiEnvironment
+        waitForIdle()
+
+        assertEquals(
+            expected = listOf("2.png", "1.png"), //MDPI - fist, Default - next
+            actual = testResourceReader.readPaths
+        )
+    }
+
     @Test
     fun testStringResourceCache() = runComposeUiTest {
         val testResourceReader = TestResourceReader()