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POWriting a paint program à la MS Paint - how to interpolate between mouse move events?
 

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  1. POWriting a paint program à la MS Paint - how to interpolate between mouse move events?
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    <p>I want to write a paint program in the style of MS Paint.</p> <p>For painting things on screen when the user moves the mouse, I have to wait for mouse move events and draw on the screen whenever I receive one. Apparently, mose move events are not sent very often, so I have to interpolate the mouse movement by drawing a line between the current mouse position and the previous one. In pseudocode, this looks something like this:</p> <pre><code>var positionOld = null def handleMouseMove(positionNew): if mouse.button.down: if positionOld == null: positionOld = positionNew screen.draw.line(positionOld,positionNew) positionOld = positionNew </code></pre> <p>Now my <strong>question</strong>: interpolating with straight line segments looks too jagged for my taste, can you recommend a better interpolation method? What method do GIMP or Adobe Photoshop implement?</p> <p>Alternatively, is there a way to increase the frequency of the mouse move events that I receive? The GUI framework I'm using is <a href="http://www.wxwidgets.org/" rel="noreferrer">wxWidgets</a>.</p> <p>GUI framework: wxWidgets.<br> (Programming language: Haskell, but that's irrelevant here)</p> <p><strong>EDIT:</strong> Clarification: I want something that looks smoother than straight line segments, see the picture (original size):</p> <p><a href="http://i26.tinypic.com/hwa42h.jpg" rel="noreferrer">jagged lines drawn between mouse positions http://i26.tinypic.com/hwa42h.jpg</a></p> <p><strong>EDIT2:</strong> The code I'm using looks like this:</p> <pre><code>-- create bitmap and derive drawing context im &lt;- imageCreateSized (sy 800 600) bitmap &lt;- bitmapCreateFromImage im (-1) -- wxBitmap dc &lt;- memoryDCCreate -- wxMemoryDC memoryDCSelectObject dc bitmap ... -- handle mouse move onMouse ... sw (MouseLeftDrag posNew _) = do ... line dc posOld posNew [color := white , penJoin := JoinRound , penWidth := 2] repaint sw -- a wxScrolledWindow -- handle paint event onPaint ... = do ... -- draw bitmap on the wxScrolledWindow drawBitmap dc_sw bitmap pointZero False [] </code></pre> <p>which might make a difference. Maybe my choices of wx-classes is why I'm getting a rather low frequency of mouse move events.</p>
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    1. USHeinrich Apfelmus
    1. USHeinrich Apfelmus
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      1. USAlexandre Jasmin
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    1. COI have no clue if this is possible, but did you consider running a timer that checks the mouse position? Then you would have control over the frequency of the messages.
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      1. USFrank Schwieterman
    2. COOoh, that's a good idea! I'll have to try that.
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      1. USHeinrich Apfelmus
 

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