Considerably faster QR-code bitmap generation

Directly assign colours to a colour buffer then use that buffer to
generate the bitmap. This is much faster than using Bitmap.setPixel for
every pixel.

Signed-off-by: Graeme Power <gjpower@tcd.ie>

CHANGES.md

@@ -17,6 +17,7 @@ Improvements 🙌:
  - Prepare changelog for F-Droid (#2296)
  - Add graphic resources for F-Droid (#812, #2220)
  - Highlight text in the body of the displayed result (#2200)
+ - Considerably faster QR-code bitmap generation (#2331)
 
 Bugfix 🐛:
  - Messages encrypted with no way to decrypt after SDK update from 0.18 to 1.0.0 (#2252)

vector/src/main/java/im/vector/app/core/qrcode/QrCode.kt

@@ -34,12 +34,15 @@ fun String.toBitMatrix(size: Int): BitMatrix {
 
 fun BitMatrix.toBitmap(@ColorInt backgroundColor: Int = Color.WHITE,
                        @ColorInt foregroundColor: Int = Color.BLACK): Bitmap {
-    val bmp = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888)
-    for (x in 0 until width) {
-        for (y in 0 until height) {
-            bmp.setPixel(x, y, if (get(x, y)) foregroundColor else backgroundColor)
+    val colorBuffer = IntArray(width*height)
+    var rowOffset = 0
+    for (y in 0 until height) {
+        for (x in 0 until width) {
+            val arrayIndex = x + rowOffset
+            colorBuffer[arrayIndex] = if (get(x, y)) foregroundColor else backgroundColor
         }
+        rowOffset += width
     }
 
-    return bmp
+    return Bitmap.createBitmap(colorBuffer, width, height, Bitmap.Config.ARGB_8888)
 }