Improve method for calculation of rectangle centers (#37092)

More numerically stable in the case of massive rectangles. This is the ultimate cause behind #36898 -- during rendering of the worldwide layer in Winkel Tripel the inverse transform fails, so the renderer sets a "maximal" filter extent for the layer (+/- double max). The previous method for calculating the rectangles center would fail, because it would overflow. The new method handles this case and correctly returns 0,0. Fixes bounding boxes show incorrectly when simplication is enabled for a layer in certain projections. Fixes #36898 Refs #30686 (partial fix -- this report includes two different bugs)
qgis · Jun 11, 2020 · 47fba10 · 47fba10
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commit 47fba10
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diff --git a/src/core/geometry/qgsrectangle.h b/src/core/geometry/qgsrectangle.h
@@ -227,7 +227,7 @@ class CORE_EXPORT QgsRectangle
     /**
      * Returns the center point of the rectangle.
      */
-    QgsPointXY center() const { return QgsPointXY( mXmin + width() / 2, mYmin + height() / 2 ); }
+    QgsPointXY center() const { return QgsPointXY( mXmax * 0.5 + mXmin * 0.5, mYmin * 0.5 + mYmax * 0.5 ); }
 
     /**
      * Scale the rectangle around its center point.

diff --git a/tests/src/core/testqgsrectangle.cpp b/tests/src/core/testqgsrectangle.cpp
@@ -43,6 +43,7 @@ class TestQgsRectangle: public QObject
     void scale();
     void snappedToGrid();
     void distanceToPoint();
+    void center();
 };
 
 void TestQgsRectangle::isEmpty()
@@ -404,5 +405,22 @@ void TestQgsRectangle::distanceToPoint()
   QGSCOMPARENEAR( rect.distance( QgsPointXY( 25, 115 ) ), 7.071068, 0.00001 );
 }
 
+void TestQgsRectangle::center()
+{
+  QgsRectangle rect( 10, 100, 20, 110 );
+  QCOMPARE( rect.center().x(), 15.0 );
+  QCOMPARE( rect.center().y(), 105.0 );
+  rect = QgsRectangle( 10, 100, 10, 100 );
+  QCOMPARE( rect.center().x(), 10.0 );
+  QCOMPARE( rect.center().y(), 100.0 );
+  rect = QgsRectangle( -10, -100, 10, 100 );
+  QCOMPARE( rect.center().x(), 0.0 );
+  QCOMPARE( rect.center().y(), 0.0 );
+  // a "maximal" rect
+  rect = QgsRectangle( std::numeric_limits<double>::lowest(), std::numeric_limits<double>::lowest(), std::numeric_limits<double>::max(), std::numeric_limits<double>::max() );
+  QCOMPARE( rect.center().x(), 0.0 );
+  QCOMPARE( rect.center().y(), 0.0 );
+}
+
 QGSTEST_MAIN( TestQgsRectangle )
 #include "testqgsrectangle.moc"
diff --git a/...p_renderer/expected_staged_render_raster/expected_staged_render_raster_mask.png b/...p_renderer/expected_staged_render_raster/expected_staged_render_raster_mask.png