greatly speed up QTransform::mapRect() for projective transforms

The code so far was converting the rect to a painterpath, mapping
that one and then taking the bounding rect. It is actually sufficient
to simply map the four corners of the rectangle and take the bounding
rect of these four points even in the projective case.

Fix the MAP macro to be more correct for degenerated projective
transformations.

Reviewed-By: Samuel

1 files changed, 5 insertions, 11 deletions

diff --git a/src/gui/painting/qtransform.cpp b/src/gui/painting/qtransform.cpp
index 385fde1..7ca3b79 100644
--- a/src/gui/painting/qtransform.cpp
+++ b/src/gui/painting/qtransform.cpp
@@ -76,7 +76,9 @@ QT_BEGIN_NAMESPACE
             nx = affine._m11 * FX_ + affine._m21 * FY_ + affine._dx;        \
             ny = affine._m12 * FX_ + affine._m22 * FY_ + affine._dy;        \
             if (t == TxProject) {                                       \
-                qreal w = 1./(m_13 * FX_ + m_23 * FY_ + m_33);              \
+                qreal w = (m_13 * FX_ + m_23 * FY_ + m_33);              \
+                if (w < Q_NEAR_CLIP) w = Q_NEAR_CLIP;                   \
+                w = 1./w;                                               \
                 nx *= w;                                                \
                 ny *= w;                                                \
             }                                                           \
@@ -1800,7 +1802,7 @@ QRect QTransform::mapRect(const QRect &rect) const
             y -= h;
         }
         return QRect(x, y, w, h);
-    } else if (t < TxProject) {
+    } else {
         // see mapToPolygon for explanations of the algorithm.
         qreal x = 0, y = 0;
         MAP(rect.left(), rect.top(), x, y);
@@ -1824,10 +1826,6 @@ QRect QTransform::mapRect(const QRect &rect) const
         xmax = qMax(xmax, x);
         ymax = qMax(ymax, y);
         return QRect(qRound(xmin), qRound(ymin), qRound(xmax)-qRound(xmin), qRound(ymax)-qRound(ymin));
-    } else {
-        QPainterPath path;
-        path.addRect(rect);
-        return map(path).boundingRect().toRect();
     }
 }
 
@@ -1870,7 +1868,7 @@ QRectF QTransform::mapRect(const QRectF &rect) const
             y -= h;
         }
         return QRectF(x, y, w, h);
-    } else if (t < TxProject) {
+    } else {
         qreal x = 0, y = 0;
         MAP(rect.x(), rect.y(), x, y);
         qreal xmin = x;
@@ -1893,10 +1891,6 @@ QRectF QTransform::mapRect(const QRectF &rect) const
         xmax = qMax(xmax, x);
         ymax = qMax(ymax, y);
         return QRectF(xmin, ymin, xmax-xmin, ymax - ymin);
-    } else {
-        QPainterPath path;
-        path.addRect(rect);
-        return map(path).boundingRect();
     }
 }