fix(icons): themed icons for custom images

app/src/main/kotlin/com/aliucord/manager/patcher/steps/patch/PatchIconsStep.kt

@@ -18,14 +18,13 @@ import com.aliucord.manager.patcher.steps.StepGroup
 import com.aliucord.manager.patcher.steps.base.Step
 import com.aliucord.manager.patcher.steps.base.StepState
 import com.aliucord.manager.patcher.steps.download.CopyDependenciesStep
-import com.aliucord.manager.patcher.util.ArscUtil
+import com.aliucord.manager.patcher.util.*
 import com.aliucord.manager.patcher.util.ArscUtil.addColorResource
 import com.aliucord.manager.patcher.util.ArscUtil.addResource
 import com.aliucord.manager.patcher.util.ArscUtil.getMainArscChunk
 import com.aliucord.manager.patcher.util.ArscUtil.getPackageChunk
 import com.aliucord.manager.patcher.util.ArscUtil.getResourceFileName
 import com.aliucord.manager.patcher.util.ArscUtil.getResourceFileNames
-import com.aliucord.manager.patcher.util.AxmlUtil
 import com.aliucord.manager.ui.screens.patchopts.PatchOptions
 import com.aliucord.manager.ui.screens.patchopts.PatchOptions.IconReplacement
 import com.aliucord.manager.util.getRawBytes
@@ -103,13 +102,17 @@ class PatchIconsStep(private val options: PatchOptions) : Step(), KoinComponent
         var foregroundIcon: BinaryResourceIdentifier? = null
         var backgroundIcon: BinaryResourceIdentifier? = null
         var monochromeIcon: BinaryResourceIdentifier? = null
+        val monochromePath = when (options.iconReplacement) {
+            is IconReplacement.CustomImage -> "res/ic_aliucord_monochrome.png"
+            else -> "res/ic_aliucord_monochrome.xml"
+        }
 
         // Add the monochrome resource and add the resource file later
         if (isMonochromeIconsAvailable) {
             container.log("Adding monochrome icon resource to arsc")
 
             val filePathIdx = arsc.getMainArscChunk().stringPool
-                .addString("res/ic_aliucord_monochrome.xml")
+                .addString(monochromePath)
 
             monochromeIcon = arsc.getPackageChunk().addResource(
                 typeName = "drawable",
@@ -177,14 +180,22 @@ class PatchIconsStep(private val options: PatchOptions) : Step(), KoinComponent
         container.log("Writing other patched files back to apk")
         ZipWriter(apk, /* append = */ true).use {
             if (isMonochromeIconsAvailable) {
-                val monochromeIconId = if (options.iconReplacement is IconReplacement.OldDiscord) {
-                    R.drawable.ic_discord_old_monochrome
-                } else {
-                    R.drawable.ic_discord_monochrome
+                val monochromeBytes = when (val icon = options.iconReplacement) {
+                    is IconReplacement.CustomImage -> {
+                        val image = BitmapFactory.decodeStream(icon.imageBytes.inputStream())
+                            ?: error("Custom icon could not be decoded")
+
+                        MonochromeMask.create(image)
+                            .also { image.recycle() }
+                    }
+
+                    is IconReplacement.OldDiscord -> context.resources.getRawBytes(R.drawable.ic_discord_old_monochrome)
+
+                    else -> context.resources.getRawBytes(R.drawable.ic_discord_monochrome)
                 }
 
-                container.log("Writing monochrome icon AXML to apk")
-                it.writeEntry("res/ic_aliucord_monochrome.xml", context.resources.getRawBytes(monochromeIconId))
+                container.log("Writing monochrome icon to apk at $monochromePath")
+                it.writeEntry(monochromePath, monochromeBytes)
             }
 
             if (options.iconReplacement is IconReplacement.OldDiscord) {

app/src/main/kotlin/com/aliucord/manager/patcher/util/MonochromeMask.kt

@@ -0,0 +1,51 @@
+package com.aliucord.manager.patcher.util
+
+import android.graphics.Bitmap
+import androidx.core.graphics.createBitmap
+import java.io.ByteArrayOutputStream
+
+object MonochromeMask {
+    /**
+     * Create a monochrome adaptive icon layer for a specific image.
+     */
+    fun create(image: Bitmap): ByteArray {
+        val width = image.width
+        val height = image.height
+
+        val pixels = IntArray(width * height)
+        image.getPixels(pixels, 0, width, 0, 0, width, height)
+
+        val hasTransparency = pixels.any { (it ushr 24 and 0xFF) < /* transparency level = */ 250 }
+
+        pixels.forEachIndexed { i, pixel ->
+            val alpha = pixel ushr 24 and 0xFF
+            val mask = if (hasTransparency) {
+                alpha
+            } else {
+                luminance(pixel) * alpha / 255
+            }
+
+            // Only replace the colors depending on alpha
+            pixels[i] = (mask shl 24) or 0xFFFFFF
+        }
+
+        val newImage = createBitmap(width, height).apply {
+            setPixels(pixels, 0, width, 0, 0, width, height)
+        }
+
+        return ByteArrayOutputStream().use {
+            newImage.compress(Bitmap.CompressFormat.PNG, 100, it)
+            newImage.recycle()
+            it.toByteArray()
+        }
+    }
+
+    // Rec. 601: Perceptual brightness, the safe default for photos and most logos
+    private fun luminance(pixel: Int): Int {
+        val red = (pixel ushr 16) and 0xFF
+        val green = (pixel ushr 8) and 0xFF
+        val blue = pixel and 0xFF
+
+        return (red * 299 + green * 587 + blue * 114) / 1000
+    }
+}