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POGraphics2D transformation result does not match manual transformation
 

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  1. POGraphics2D transformation result does not match manual transformation
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    <p>I am using Java's Graphics2D to draw on a component using AffineTransform's to manipulate my drawing. Graphics2D offers an method transform for this, which takes an AffineTransform.</p> <p>Sometimes I need to manipulate a point manually without using the builtin-transformation. But when I try to transform a point using the same transformation I gave to Graphics2D.transform sometimes the resulting point is not the same.</p> <p>The following code reproduces the problem (It's Scala code, but I think you can imagine the Java code.):</p> <pre><code> var transformationMatrix = new AffineTransform() /* * transformationMatrix is modified throughout the program * ... */ override def paintComponent(g: Graphics2D) = { super.paintComponent(g) /* 1. transform using graphics transform */ g.transform(transformationMatrix) g.setColor(Color.RED) g.fill(new Rectangle(0, 0, 1, 1)) /* 2. transform point manually */ g.setTransform(new AffineTransform) // reset transformation to standard val p0 = new Point(0, 0) val pDest = new Point() transformationMatrix.transform(p0, pDest) g.setColor(Color.BLUE) g.fill(new Rectangle(pDest.x, pDest.y, 1, 1) } </code></pre> <p><strong>Expected behaviour</strong></p> <p>The blue rectangle (manually calculated) overdraws the red one (calculated by transform).</p> <p><strong>Experienced behaviour</strong></p> <p><img src="https://i.stack.imgur.com/RmEnU.png" alt="The blue rectangle has an offset of 1"></p> <p>I admit that my transformationMatrix is not really integer, but that should'nt be the problem, should it?</p> <pre><code> affineTransform = 1.1, 0.0, 520.55 0.0, 1.1, 182.54999999999995 0.0, 0.0, 1.0 </code></pre> <p>Is this a bug or am I missing some deep insight?</p> <p><strong>Edit</strong>: You can <em>reproduce</em> the bug, if you set transformationMatrix to</p> <pre><code>transformationMatrix = new AffineTransform(1.1, 0.0, 0.0, 1.1, 521.55, 183.54999999999995) </code></pre> <p>at the beginning of paintComponent. Please note, that g is of type Graphics2D.</p>
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    1. COI wonder if there may be a different transform active when paint() is called. I would try g.getTransform() at the start of the method and use the result to restore the 'standard' transform.
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    2. COThat does not help either. g.getTransform() returns identity matrix and saving it and restoring later leads to the same behaviour.
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