Databases
StackOverflow2013
Postsdbo
POArtifacts when trying to draw background grid without anti-aliasing in a QGraphicsScene
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POArtifacts when trying to draw background grid without anti-aliasing in a QGraphicsScene
    primarykey
    data
    text
    <p>I'm trying to draw a background grid in the drawBackground() function of my QGraphicsScene subclass:</p> <pre><code>void Scene::drawBackground(QPainter *painter, const QRectF &amp;rect) { const int gridSize = 50; const int realLeft = static_cast&lt;int&gt;(std::floor(rect.left())); const int realRight = static_cast&lt;int&gt;(std::ceil(rect.right())); const int realTop = static_cast&lt;int&gt;(std::floor(rect.top())); const int realBottom = static_cast&lt;int&gt;(std::ceil(rect.bottom())); // Draw grid. const int firstLeftGridLine = realLeft - (realLeft % gridSize); const int firstTopGridLine = realTop - (realTop % gridSize); QVarLengthArray&lt;QLine, 100&gt; lines; for (qreal x = firstLeftGridLine; x &lt;= realRight; x += gridSize) lines.append(QLine(x, realTop, x, realBottom)); for (qreal y = firstTopGridLine; y &lt;= realBottom; y += gridSize) lines.append(QLine(realLeft, y, realRight, y)); //painter-&gt;setRenderHint(QPainter::Antialiasing); painter-&gt;setPen(QPen(QColor(220, 220, 220), 0.0)); painter-&gt;drawLines(lines.data(), lines.size()); // Draw axes. painter-&gt;setPen(QPen(Qt::lightGray, 0.0)); painter-&gt;drawLine(0, realTop, 0, realBottom); painter-&gt;drawLine(realLeft, 0, realRight, 0); } </code></pre> <p>However, unless I turn on anti-aliasing, moving items around will sometimes leave artifacts in the grid (areas where it's not drawn). It seems it mostly happens at low zoom levels, when the view is zoomed out a bit. Any ideas what I might be doing wrong here?</p> <p>I'd really don't want to turn anti-aliasing on since the lines are strictly horizontal and vertical, and I'd like them to be as crisp as possible.</p> <p>Any help is much appriciated, Regards, Elvis</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USestan
    plurals
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POArtifacts when trying to draw background grid without anti-aliasing in a QGraphicsScene
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POArtifacts when trying to draw background grid without anti-aliasing in a QGraphicsScene
      1. This table or related slice is empty.
      1. VTUpMod
    1. COHave you tried explicitly erasing the contents of the scene before drawing? Try drawing a rectangle of white (or whatever your background colour is) before drawing your gridlines, and see if that helps.
      singulars
      1. POArtifacts when trying to draw background grid without anti-aliasing in a QGraphicsScene
      1. USThomi
    2. COHave you tried calling the base class function first? Maybe it is supposed to erase the background first: `QGraphicsScene::drawBackground(painter, rect)`, and then all your custom code.
      singulars
      1. POArtifacts when trying to draw background grid without anti-aliasing in a QGraphicsScene
      1. USak.
    3. COhave you tried calling setViewportUpdateMode(QGraphicsView::FullViewportUpdate) at the start of your program?
      singulars
      1. POArtifacts when trying to draw background grid without anti-aliasing in a QGraphicsScene
      1. USTom
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload