Changeset 74

Timestamp:

Mar 26, 2006, 4:09:02 PM (19 years ago)

Author:

dmik

Message:

More QCanvas fixes: forced the transformation mode to be Areas in some sensitive places (for example, when drawing the background); reimplemented the "garbage on the edges" removal fix.

File:

• trunk/src/canvas/qcanvas.cpp (modified) (9 diffs)

trunk/src/canvas/qcanvas.cpp

@@ -49 +49 @@
 #include <stdlib.h>
 
-//#define QT_NO_CANVAS_ROUNDING_FIX
+// QT_NO_CANVAS_ROUNDING_FIX macro encloses some hacks to QCanvas intended
+// to get rid of artefacts and distortions caused by rounding errors. These
+// hacks give much better results when the canvas is scaled, sheared or
+// rotated in the canvas view; however they are just quick patches and not
+// perfect -- there are still some artefacts possible in rare cases. As far
+// as I understand, there is a general problem in the QCanvas design: it
+// operates on integers (instead of doubles) when doing series of direct and
+// inverse transformations in a row, that results in a big inaccuracy (more
+// than one pixel in some cases).
+//
+// So far, this fix is tested on OS/2 only, so it is disabled for other
+// platforms.
+
+#if !defined(Q_WS_PM)
+#define QT_NO_CANVAS_ROUNDING_FIX
+#endif
 
 #if !defined(QT_NO_TRANSFORMATIONS) && !defined(QT_NO_CANVAS_ROUNDING_FIX)
@@ -193 +208 @@
 }
 
-/*!
- * \internal
- *
- * Similar to mapRectMax, but with the opposite meaning. Tries to return
- * a region that is completely inside the given rectangle after transformation.
- * \a br is the target bounding rectangle (to minimize calculations).
- *
- * Using this function to clip out areas of the canvas view not covered by the
- * canvas eliminates garbage at canvas edges that can be well seen when the
- * canvas is rotated in the view.
- */
-static
-QRegion mapRectMin( const QWMatrix &m, const QRect &r, const QRect &br )
-{
-    QRegion rgn;
-    
-    if ( m.isIdentity() ) {
-        rgn = QRegion( r );
-        return rgn; 
-    }
-
-    if ( m.m12() == 0.0 && m.m21() == 0.0 ) {
-        QRect rect = r;    
-        // make bottom right exclusive
-        ++ rect.rBottom();
-        ++ rect.rRight();
-        double x1, y1, x2, y2;
-        // no shear or rotation, map two coords
-        m.map( rect.left(), rect.top(), &x1, &y1 );
-        m.map( rect.right(), rect.bottom(), &x2, &y2 );
-        // get integers (partially covered points are excluded)
-        x1 = ceil( x1 );
-        y1 = ceil( y1 );
-        x2 = floor( x2 );
-        y2 = floor( y2 );
-        // compose the result
-        rect.setCoords( int( x1 ), int( y1 ), int( x2 ), int( y2 ) );
-        // make bottom right inclusive again
-        -- rect.rBottom();
-        -- rect.rRight();
-        rgn = QRegion( rect );
-    } else {
-        // make the rectangle smaller to compensate for differences in
-        // line drawing routines of the underlying OS (when defining regions
-        // from polygons) and by Qt tansformations (when transforming images
-        // or when determining invalid chunks)
-        QPointArray pa( r );
-        pa = m.map( pa );
-        rgn = QRegion( pa );
-        // limit to the bounding rect (expanded to compensate shifts)
-        QRect rect = br;
-        rect.addCoords( -1, 0, 1, 0 );
-        rgn &= QRegion( rect );
-        // create a copy of the region and shift each towards other by 1 pixel
-        // to compensate for (clip out) differences in line drawing routines of
-        // the underlying OS (when defining regions from polygons) and in Qt
-        // tansformation routines (when transforming images or when determining
-        // invalid chunks)
-        QRegion rgn2 = rgn;
-        rgn.translate( 1, 0 );
-        rgn2.translate( -1, 0 );
-        // take an intersection
-        rgn &= rgn2;
-    }
-    
-    return rgn;
-}
-
 #endif
 
@@ -1226 +1173 @@
     QRect ivr = vr;
     if ( wm.m12() != 0.0 || wm.m21() != 0.0 ) {
-        // compensate for rounding errors happening on the path
+        // Compensate for rounding errors happening somewhere on the path
         // update() -> drawViewArea() after many transformations (can be seen
-        // when moving items in a canvas view that makes the canvas smaller
+        // when moving items in a canvas view that scales the canvas down
         // and rotates it to ~270 degress clockwise)
         ivr.addCoords( -1, -1, 1, 1 );
@@ -1248 +1195 @@
 
 #ifndef QT_NO_TRANSFORMATIONS
-#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
-        QRect cvr = vr; cvr.moveBy(tl.x(),tl.y());
-        QRegion ra = mapRectMin( wm * twm, all, cvr ); 
-#else        
 #if !defined(Q_WS_PM)
         // For translation-only transformation, it is safe to include the right
@@ -1267 +1210 @@
         QPointArray a( all );
 #endif
+#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
+        QWMatrix::TransformationMode oldMode = QWMatrix::transformationMode();
+        QWMatrix::setTransformationMode( QWMatrix::Areas );
+#endif        
         a = (wm*twm).map(a);
+#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
+        QWMatrix::setTransformationMode( oldMode );
 #endif        
-#else
+#else // QT_NO_TRANSFORMATIONS
 #if !defined(Q_WS_PM)
         QPointArray a( QRect(all.x(),all.y(),all.width()+1,all.height()+1) );
@@ -1277 +1226 @@
 #endif
         if ( view->viewport()->backgroundMode() == NoBackground ) {
-#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
-            p->setClipRegion( QRegion( cvr ) - ra );
-#else
             QRect cvr = vr; cvr.moveBy(tl.x(),tl.y());
             p->setClipRegion(QRegion(cvr)-QRegion(a));
-#endif 
             p->fillRect(vr,view->viewport()->palette()
                 .brush(QPalette::Active,QColorGroup::Background));
         }
-#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
-        p->setClipRegion( ra );
-#else
         p->setClipRegion(a);
-#endif            
     }
 
@@ -1364 +1305 @@
                     p.translate(tl.x(),tl.y());
 #if !defined(QT_NO_CANVAS_ROUNDING_FIX)
-                    drawViewArea( view, &p, mapRectMax( wm, r ), dblbuf );
+                    QRect vr = mapRectMax( wm, r );
+                    if ( wm.m12() != 0.0 || wm.m21() != 0.0 ) {
+                        // Compensate for rounding errors happening sometimes
+                        // after two direct and inverse transformations
+                        vr.addCoords( 0, 0, 1, 1 );
+                    }
+                    drawViewArea( view, &p, vr, dblbuf );
 #else
                     drawViewArea( view, &p, wm.map(r), dblbuf );
@@ -1614 +1561 @@
     allvisible.sort();
 
+#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
+    QRect safeArea = area;
+    if (p && !p->worldMatrix().isIdentity()) {
+        // Increase bounds that lay on the edges to get rid of drawing artefacts
+        // caused by differeces in regions defined using 4 points and rectangles
+        // drawn under the non-identity matrix
+        if ( area.x() == 0 ) safeArea.rLeft() -= 2;
+        if ( area.y() == 0 ) safeArea.rTop() -= 2;
+        if ( area.right() == width() - 1 ) safeArea.rRight() += 2;
+        if ( area.bottom() == height() - 1 ) safeArea.rBottom() += 2;
+    }
+
+    // Force the transformation mode to Areas. W/o this, drawBackground() and
+    // drawForeground() will not fill the canvas correctly when scaling up
+    // takes place.
+    QWMatrix::TransformationMode oldMode = QWMatrix::transformationMode();
+    QWMatrix::setTransformationMode( QWMatrix::Areas );
+#endif
+    
     if ( double_buffer )
         ensureOffScrSize( area.width(), area.height() );
@@ -1622 +1588 @@
         painter.translate(-area.x(),-area.y());
         if ( p ) {
+#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
+            QRect r = safeArea;
+            r.moveBy (-area.x(), -area.y());
+            painter.setClipRect(r);
+#else
             painter.setClipRect(QRect(0,0,area.width(),area.height()));
+#endif
         } else {
             painter.setClipRegion(rgn);
         }
+#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
+        drawBackground(painter,safeArea);
+#else
         drawBackground(painter,area);
+#endif
         allvisible.drawUnique(painter);
+#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
+        drawForeground(painter,safeArea);
+#else
         drawForeground(painter,area);
+#endif
         painter.end();
         if ( p ) {
             p->drawPixmap( area.x(), area.y(), offscr,
                 0, 0, area.width(), area.height() );
-            return;
         }
     } else if ( p ) {
+#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
+        drawBackground(*p,safeArea);
+#else
         drawBackground(*p,area);
+#endif
         allvisible.drawUnique(*p);
+#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
+        drawForeground(*p,safeArea);
+#else
         drawForeground(*p,area);
-        return;
-    }
-
+#endif
+    }
+
+    if ( p )
+        return;
+    
+#if !defined(QT_NO_CANVAS_ROUNDING_FIX)
+    QWMatrix::setTransformationMode( oldMode );
+#endif
+    
     QPoint trtr; // keeps track of total translation of rgn