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POWhy is my c# paint method running out of memory?
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copied!<p>I'm new to c#, and trying to learn by writing some simple apps to get familiar with the syntax and .NET library. The most recent miniproject I took on is a polar clock <a href="http://vis.stanford.edu/protovis/ex/clock.html" rel="nofollow noreferrer">like the one found here</a>.</p> <p>One of the problems I noticed early on was that the app would constantly "flicker", which really took away from the presentation, so I read online about how to implement a double buffer, which eliminated this problem, but may or may not have something to do with the problem. Here is my <code>onPaint</code> method; it is called every 33ms (~30 FPS) by a timer control. Most of the rest of the app is simply handlers for dragging the app (since it is frameless and has a transparent background), exiting on double-click, etc.</p> <pre><code> protected override void OnPaint(PaintEventArgs e) { DateTime now = DateTime.Now; float secondAngle = now.Second / 60F; secondAngle += (now.Millisecond / 1000F) * (1F / 60F); float minuteAngle = now.Minute / 60F; minuteAngle += secondAngle / 60F; float hourAngle = now.Hour / 24F; hourAngle += minuteAngle / 60F; float dayOfYearAngle = now.DayOfYear / (365F + (now.Year % 4 == 0 ? 1F : 0F)); dayOfYearAngle += hourAngle / 24F; float dayOfWeekAngle = (float)(now.DayOfWeek + 1) / 7F; dayOfWeekAngle += hourAngle / 24F; float dayOfMonthAngle = (float)now.Day / (float)DateTime.DaysInMonth(now.Year, now.Month); dayOfMonthAngle += hourAngle / 24F; float monthAngle = now.Month / 12F; monthAngle += dayOfMonthAngle / (float)DateTime.DaysInMonth(now.Year, now.Month); float currentPos = brushWidth / 2F; float[] angles = { secondAngle, minuteAngle, hourAngle, dayOfYearAngle, dayOfWeekAngle, dayOfMonthAngle, monthAngle }; SolidBrush DateInfo = new SolidBrush(Color.Black); SolidBrush background = new SolidBrush(Color.Gray); Pen lineColor = new Pen(Color.Blue, brushWidth); Font DateFont = new Font("Arial", 12); if (_backBuffer == null) { _backBuffer = new Bitmap(this.Width, this.Height); } Graphics g = Graphics.FromImage(_backBuffer); g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias; try { g.Clear(Color.White); if (_mouseIsOver) { g.FillEllipse(background, new Rectangle(0, 0, this.Width, this.Height)); } foreach (float angle in angles) { g.DrawArc( lineColor, currentPos, currentPos, this.Height - currentPos * 2, this.Width - currentPos * 2, startAngle, angle * 360F ); currentPos += brushWidth + spaceStep; } // Text - Seconds g.DrawString(String.Format("{0:D2} s", now.Second), DateFont, DateInfo, new PointF(115F, 0F)); g.DrawString(String.Format("{0:D2} m", now.Minute), DateFont, DateInfo, new PointF(115F, 20F)); g.DrawString(String.Format("{0:D2} h", now.Hour), DateFont, DateInfo, new PointF(115F, 40F)); g.DrawString(String.Format("{0:D3}", now.DayOfYear), DateFont, DateInfo, new PointF(115F, 60F)); g.DrawString(now.ToString("ddd"), DateFont, DateInfo, new PointF(115F, 80F)); g.DrawString(String.Format("{0:D2} d", now.Day), DateFont, DateInfo, new PointF(115F, 100F)); g.DrawString(now.ToString("MMM"), DateFont, DateInfo, new PointF(115F, 120F)); g.DrawString(now.ToString("yyyy"), DateFont, DateInfo, new PointF(115F, 140F)); e.Graphics.DrawImageUnscaled(_backBuffer, 0, 0); } finally { g.Dispose(); DateInfo.Dispose(); background.Dispose(); DateFont.Dispose(); lineColor.Dispose(); } //base.OnPaint(e); } protected override void OnPaintBackground(PaintEventArgs e) { //base.OnPaintBackground(e); } protected override void OnResize(EventArgs e) { if (_backBuffer != null) { _backBuffer.Dispose(); _backBuffer = null; } base.OnResize(e); } </code></pre> <p>I thought by disposing of everything at the end of the method I'd be safe, but it doesn't seem to help. Furthermore, the interval between run-time and the OutOfMemoryException isn't constant; once it happened only a few seconds in, but usually it takes a minute or two. Here are some class-wide variable declarations.</p> <pre><code> private Bitmap _backBuffer; private float startAngle = -91F; private float brushWidth = 14; private float spaceStep = 6; </code></pre> <p>And a screenshot (edit: screenshot links to a view with some code present):</p> <p><a href="http://www.ggot.org/inexplicable/pc.jpg" rel="nofollow noreferrer">Screenshot http://www.ggot.org/inexplicable/pc2.jpg</a></p> <p>EDIT: Stacktrace!</p> <pre><code>System.OutOfMemoryException: Out of memory. at System.Drawing.Graphics.CheckErrorStatus(Int32 status) at System.Drawing.Graphics.DrawArc(Pen pen, Single x, Single y, Single width, Single height, Single startAngle, Single sweepAngle) at PolarClock.clockActual.OnPaint(PaintEventArgs e) in C:\Redacted\PolarClock\clockActual.cs:line 111 at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer, Boolean disposeEventArgs) at System.Windows.Forms.Control.WmPaint(Message& m) at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) </code></pre> <p>Seems to be the same line it crashed on last time, the main <code>drawArc</code> inside the loop.</p>

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