From 449a8089728deae785faead28476a10cf5990be0 Mon Sep 17 00:00:00 2001
From: Milian Wolff <milian.wolff@kdab.com>
Date: Mon, 19 Dec 2016 18:20:47 +0100
Subject: [PATCH] Crop to capture rect directly when converting RGB to
 grayscale

This improves the performance since we only need to convert the
actually interesting part of the frame, instead of the full frame.
---
 examples/QZXingLive/QZXingFilter.cpp | 55 +++++++++++++++++-----------
 1 file changed, 34 insertions(+), 21 deletions(-)

diff --git a/examples/QZXingLive/QZXingFilter.cpp b/examples/QZXingLive/QZXingFilter.cpp
index 7b03d5f..31ca5a9 100644
--- a/examples/QZXingLive/QZXingFilter.cpp
+++ b/examples/QZXingLive/QZXingFilter.cpp
@@ -108,24 +108,37 @@ QVideoFrame QZXingFilterRunnable::run(QVideoFrame * input, const QVideoSurfaceFo
 static QImage rgbDataToGrayscale(const uchar* data, const int width, const int height,
                                  const int alpha, const int red,
                                  const int green, const int blue,
+                                 const QRect& captureRect,
                                  const bool isPremultiplied = false)
 {
-    QImage image(width, height, QImage::Format_Grayscale8);
-    uchar* pixel = image.bits();
-    uchar* const pixelEnd = pixel + (width * height);
     const int stride = (alpha < 0) ? 3 : 4;
 
-    for (; pixel != pixelEnd; ++pixel, data += stride) {
-        uchar r = data[red];
-        uchar g = data[green];
-        uchar b = data[blue];
-        if (isPremultiplied) {
-            uchar a = data[alpha];
-            r = (uint(r) * 255) / a;
-            g = (uint(g) * 255) / a;
-            b = (uint(b) * 255) / a;
+    const int startX = captureRect.x();
+    const int startY = captureRect.y();
+    const int targetWidth = captureRect.isNull() ? width : captureRect.width();
+    const int targetHeight = captureRect.isNull() ? height : captureRect.height();
+    const int endX = width - startX - targetWidth;
+    const int skipX = (endX + startX) * stride;
+
+    QImage image(targetWidth, targetHeight, QImage::Format_Grayscale8);
+    uchar* pixel = image.bits();
+    data += (startY * width + startX) * stride;
+    for (int y = 0; y < targetHeight; ++y) {
+        for (int x = 0; x < targetWidth; ++x) {
+            uchar r = data[red];
+            uchar g = data[green];
+            uchar b = data[blue];
+            if (isPremultiplied) {
+                uchar a = data[alpha];
+                r = (uint(r) * 255) / a;
+                g = (uint(g) * 255) / a;
+                b = (uint(b) * 255) / a;
+            }
+            *pixel = gray(r, g, b);
+            ++pixel;
+            data += stride;
         }
-        *pixel = gray(r, g, b);
+        data += skipX;
     }
     return image;
 }
@@ -143,19 +156,19 @@ void QZXingFilterRunnable::processVideoFrameProbed(SimpleVideoFrame & videoFrame
 
     /// Let's try to convert it from RGB formats
     if (videoFrame.pixelFormat == QVideoFrame::Format_RGB32)
-        image = rgbDataToGrayscale(data, width, height, -1, 1, 2, 3);
+        image = rgbDataToGrayscale(data, width, height, -1, 1, 2, 3, captureRect);
     else if (videoFrame.pixelFormat == QVideoFrame::Format_ARGB32)
-        image = rgbDataToGrayscale(data, width, height, 0, 1, 2, 3);
+        image = rgbDataToGrayscale(data, width, height, 0, 1, 2, 3, captureRect);
     else if (videoFrame.pixelFormat == QVideoFrame::Format_ARGB32_Premultiplied)
-        image = rgbDataToGrayscale(data, width, height, 0, 1, 2, 3, true);
+        image = rgbDataToGrayscale(data, width, height, 0, 1, 2, 3, captureRect, true);
     else if (videoFrame.pixelFormat == QVideoFrame::Format_BGRA32)
-        image = rgbDataToGrayscale(data, width, height, 3, 2, 1, 0);
+        image = rgbDataToGrayscale(data, width, height, 3, 2, 1, 0, captureRect);
     else if (videoFrame.pixelFormat == QVideoFrame::Format_BGRA32_Premultiplied)
-        image = rgbDataToGrayscale(data, width, height, 3, 2, 1, 0, true);
+        image = rgbDataToGrayscale(data, width, height, 3, 2, 1, 0, captureRect, true);
     else if (videoFrame.pixelFormat == QVideoFrame::Format_BGR32)
-        image = rgbDataToGrayscale(data, width, height, 3, 2, 1, 0);
+        image = rgbDataToGrayscale(data, width, height, 3, 2, 1, 0, captureRect);
     else if (videoFrame.pixelFormat == QVideoFrame::Format_BGR24)
-        image = rgbDataToGrayscale(data, width, height, -1, 2, 1, 0);
+        image = rgbDataToGrayscale(data, width, height, -1, 2, 1, 0, captureRect);
 
     /// This is a forced "conversion", colors end up swapped.
     if(image.isNull() && videoFrame.pixelFormat == QVideoFrame::Format_BGR555)
@@ -225,7 +238,7 @@ void QZXingFilterRunnable::processVideoFrameProbed(SimpleVideoFrame & videoFrame
         return;
     }
 
-    if (!captureRect.isEmpty())
+    if (!captureRect.isEmpty() && image.size() != captureRect.size())
         image = image.copy(captureRect);
 
 //    qDebug() << "image.size()" << image.size();