Fix pixel-alignment of the Rectangle and Ellipse tools

Now there are a bit complex rules of rounding, but they do exactly
what the user expects from the tool.

BUG:334508

krita/ui/tool/kis_tool_ellipse_base.cpp

@@ -31,8 +31,12 @@ KisToolEllipseBase::KisToolEllipseBase(KoCanvasBase * canvas, KisToolEllipseBase
 {
 }
 
-void KisToolEllipseBase::paintRectangle(QPainter &gc, const QRect &viewRect)
+void KisToolEllipseBase::paintRectangle(QPainter &gc, const QRectF &imageRect)
 {
+    KIS_ASSERT_RECOVER_RETURN(canvas());
+
+    QRect viewRect = pixelToView(imageRect).toRect();
+
     QPainterPath path;
     path.addEllipse(viewRect);
     paintToolOutline(&gc, path);

krita/ui/tool/kis_tool_ellipse_base.h

@@ -28,7 +28,7 @@ class KRITAUI_EXPORT KisToolEllipseBase : public KisToolRectangleBase
 public:
     KisToolEllipseBase(KoCanvasBase * canvas, KisToolEllipseBase::ToolType type, const QCursor & cursor=KisCursor::load("tool_ellipse_cursor.png", 6, 6));
 
-    void paintRectangle(QPainter &gc, const QRect &viewRect);
+    void paintRectangle(QPainter &gc, const QRectF &imageRect);
 };
 
 #endif // KIS_TOOL_ELLIPSE_BASE_H

krita/ui/tool/kis_tool_rectangle_base.cpp

@@ -18,6 +18,9 @@
  */
 
 #include "kis_tool_rectangle_base.h"
+
+#include <QtCore/qmath.h>
+
 #include <KoPointerEvent.h>
 #include <KoCanvasBase.h>
 #include <KoCanvasController.h>
@@ -35,7 +38,7 @@ KisToolRectangleBase::KisToolRectangleBase(KoCanvasBase * canvas, KisToolRectang
 void KisToolRectangleBase::paint(QPainter& gc, const KoViewConverter &converter)
 {
     if(mode() == KisTool::PAINT_MODE) {
-        paintRectangle(gc, pixelToView(QRectF(m_dragStart, m_dragEnd)).toRect());
+        paintRectangle(gc, createRect(m_dragStart, m_dragEnd));
     }
 
     KisToolPaint::paint(gc, converter);
@@ -105,14 +108,41 @@ void KisToolRectangleBase::endPrimaryAction(KoPointerEvent *event)
 
     updateArea();
 
-    finishRect(QRectF(m_dragStart, m_dragEnd).normalized());
+    finishRect(createRect(m_dragStart, m_dragEnd));
     event->accept();
 }
 
-void KisToolRectangleBase::paintRectangle(QPainter &gc, const QRect &viewRect)
+QRectF KisToolRectangleBase::createRect(const QPointF &start, const QPointF &end)
+{
+    /**
+     * To make the dragging user-friendly it should work in a bit
+     * non-obvious way: the start-drag point must be handled with
+     * "ceil"/"floor" (depending on the direction of the drag) and the
+     * end-drag point should follow usual "round" semantics.
+     */
+
+    qreal x0 = start.x();
+    qreal y0 = start.y();
+    qreal x1 = end.x();
+    qreal y1 = end.y();
+
+    int newX0 = x1 - x0 > 0 ? qCeil(x0) : qFloor(x0);
+    int newY0 = y1 - y0 > 0 ? qCeil(y0) : qFloor(y0);
+
+    int newX1 = qRound(x1);
+    int newY1 = qRound(y1);
+
+    QRectF result;
+    result.setCoords(newX0, newY0, newX1, newY1);
+    return result.normalized();
+}
+
+void KisToolRectangleBase::paintRectangle(QPainter &gc, const QRectF &imageRect)
 {
     KIS_ASSERT_RECOVER_RETURN(canvas());
 
+    QRect viewRect = pixelToView(imageRect).toAlignedRect();
+
     QPainterPath path;
     path.addRect(viewRect);
     paintToolOutline(&gc, path);

krita/ui/tool/kis_tool_rectangle_base.h

@@ -50,9 +50,8 @@ protected:
     ToolType m_type;
 
     void updateArea();
-    virtual void paintRectangle(QPainter &gc, const QRect &viewRect);
-
-
+    virtual void paintRectangle(QPainter &gc, const QRectF &imageRect);
+    virtual QRectF createRect(const QPointF &start, const QPointF &end);
 };
 
 #endif // KIS_TOOL_RECTANGLE_BASE_H