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POConnecting QPixmaps with the data being drawn on them
 

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  1. POConnecting QPixmaps with the data being drawn on them
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    <p>I am looking for a way to connect the QPixmap and the data being written on it, so that in the end I can have an accurate record of what is currently on the screen.</p> <pre><code>void QPainter::drawRects(const QRectF *rects, int rectCount) </code></pre> <p>This is an example function from qpainter.cpp (found in ./src/gui/painting in the Qt SDK) What I am trying to get is the Pixmap that the rectangle is being written to (in the case when device()->devType() is a Pixmap). So I have this check:</p> <pre><code>if(this-&gt;device()-&gt;devType() == QInternal::Pixmap) { const QPixmap *Pixmap = dynamic_cast&lt;const QPixmap *&gt;(this-&gt;device()); qDebug() &lt;&lt; "rect2pixmap - address: "&lt;&lt;Pixmap&lt;&lt;" - key: "&lt;&lt;Pixmap.cacheKey(); } </code></pre> <p>I tried finding the memory address of the Qpixmap and checking it against the memory addresses of the QPixmaps being written to the screen.</p> <pre><code>void QPainter::drawPixmap(const QPointF &amp;p, const QPixmap &amp;pm) { const QWidget *widget = dynamic_cast&lt;const QWidget *&gt;(this-&gt;device()); qDebug() &lt;&lt; "pixmap - address: "&lt;&lt;&amp;pm &lt;&lt; " - key: "&lt;&lt;pm.cacheKey(); [...] </code></pre> <p>But the addresses are all different. I also tried using cachekeys, but I faced the same problem.</p> <p>Here's a sample console output:</p> <pre><code>rect2pixmap - address: 0x7fffac1dc9c0 - key: 72057594037927937 rect2pixmap - address: 0x7fffac1d9f80 - key: 72057598332895233 rect2pixmap - address: 0x7fffac1dcd60 - key: 72057602627862529 rect2pixmap - address: 0x7fffac1dcd60 - key: 72057606922829825 rect2pixmap - address: 0x7fffac1dd100 - key: 72057611217797121 rect2pixmap - address: 0x7fffac1df2e0 - key: 72057615512764417 pixmap - address: 0x7fffac1dffa0 - key: 197568495616 pixmap - address: 0x7fffac1e0170 - key: 214748364800 pixmap - address: 0x7fffac1e0340 - key: 231928233984 pixmap - address: 0x7fffac1e0510 - key: 249108103168 pixmap - address: 0x7fffac1e06e0 - key: 261993005056 rect2pixmap - address: 0x7fffac1dadb0 - key: 72057619807731713 </code></pre> <p>So what I am asking is there anyway to link between the pixmap that the rect is being written to and the pixmap that is being printed later on to the screen? And can I safely assume that the rects aren't being shown on the screen if no Pixmaps are ever called?</p> <p>If anything isn't clear abut the question, please tell me, and I'll try to clarify as best as I can.</p> <p>Thank you.</p>
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    1. USRaghd Hamzeh
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    1. COSo you want to draw something onto some QPixmaps and then draw the QPixmaps onto a painter?
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      1. USStephen Chu
    2. COI'm trying to keep track of whatever is being drawn to the screen. Using widgets and internal elements I can get that, but with Pixmaps, it becomes trickier, since I can't map elements globally, and because pixmaps are usually drawn later to the screen. So any rect, or line drawn to a Pixmap would pose a problem because a) I do not know when it is actually drawn to the screen, and b) I do not know where it's global position lies.
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      1. USRaghd Hamzeh
    3. COIf the goal is to track and link individual graphic elements to your data, you may want to consider a different approach. I would use QGraphicsScene and QGraphicsItems for that.
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      1. USStephen Chu
 

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