TrimTransformation for images

app/src/main/java/org/koitharu/kotatsu/core/ui/uiModule.kt

@@ -29,6 +29,9 @@ val uiModule
 			ImageLoader.Builder(androidContext())
 				.okHttpClient(httpClientFactory)
 				.interceptorDispatcher(Dispatchers.Default)
+				.fetcherDispatcher(Dispatchers.IO)
+				.decoderDispatcher(Dispatchers.Default)
+				.transformationDispatcher(Dispatchers.Default)
 				.diskCache(diskCacheFactory)
 				.components(
 					ComponentRegistry.Builder()

app/src/main/java/org/koitharu/kotatsu/utils/image/TrimTransformation.kt

@@ -0,0 +1,96 @@
+package org.koitharu.kotatsu.utils.image
+
+import android.graphics.Bitmap
+import androidx.core.graphics.get
+import coil.size.Size
+import coil.transform.Transformation
+
+class TrimTransformation : Transformation {
+
+	override val cacheKey: String = javaClass.name
+
+	override suspend fun transform(input: Bitmap, size: Size): Bitmap {
+		var left = 0
+		var top = 0
+		var right = 0
+		var bottom = 0
+
+		// Left
+		for (x in 0 until input.width) {
+			var isColBlank = true
+			val prevColor = input[x, 0]
+			for (y in 1 until input.height) {
+				if (input[x, y] != prevColor) {
+					isColBlank = false
+					break
+				}
+			}
+			if (isColBlank) {
+				left++
+			} else {
+				break
+			}
+		}
+		if (left == input.width) {
+			return input
+		}
+		// Right
+		for (x in (left until input.width).reversed()) {
+			var isColBlank = true
+			val prevColor = input[x, 0]
+			for (y in 1 until input.height) {
+				if (input[x, y] != prevColor) {
+					isColBlank = false
+					break
+				}
+			}
+			if (isColBlank) {
+				right++
+			} else {
+				break
+			}
+		}
+		// Top
+		for (y in 0 until input.height) {
+			var isRowBlank = true
+			val prevColor = input[0, y]
+			for (x in 1 until input.width) {
+				if (input[x, y] != prevColor) {
+					isRowBlank = false
+					break
+				}
+			}
+			if (isRowBlank) {
+				top++
+			} else {
+				break
+			}
+		}
+		// Bottom
+		for (y in (top until input.height).reversed()) {
+			var isRowBlank = true
+			val prevColor = input[0, y]
+			for (x in 1 until input.width) {
+				if (input[x, y] != prevColor) {
+					isRowBlank = false
+					break
+				}
+			}
+			if (isRowBlank) {
+				bottom++
+			} else {
+				break
+			}
+		}
+
+		return if (left != 0 || right != 0 || top != 0 || bottom != 0) {
+			Bitmap.createBitmap(input, left, top, input.width - left - right, input.height - top - bottom)
+		} else {
+			input
+		}
+	}
+
+	override fun equals(other: Any?) = other is TrimTransformation
+
+	override fun hashCode() = javaClass.hashCode()
+}