[Gtk-sharp-list] Access Violations with Mono.Cairo on Windows
m.j.hutchinson at gmail.com
Tue Dec 29 22:45:28 EST 2009
On Tue, Dec 29, 2009 at 9:20 AM, Andy Selvig <ajselvig at gmail.com> wrote:
> First of all, this is a Mono.Cairo question and I've noticed there's a lot
> of experience with it on this list, but if there's a better place to
> discuss, please let me know.
> I've working on a project using Mono.Cairo. Most of my recent development
> has been on Linux and everything is working well. However, I recently tried
> to run the project on Windows and I keep getting access violations from
> Cairo calls:
> "Attempted to read or write protected memory. This is often an indication
> that other memory is corrupt."
> The part of the code this seems to be happening in is when I create a Cairo
> image surface and render to it. It looks something like this:
> // remake the image surface, if needed
> if (surface == null || surface.Width != IntWidth ||
> surface.Height != IntHeight)
> imageData = new byte[IntWidth * IntHeight * 4];
> surface = new ImageSurface( ref imageData, Format.ARGB32,
> IntWidth, IntHeight, 4 * IntWidth);
> // render the control to the surface
> using (Context cr = new Context(surface))
> cr.Operator = Operator.Source;
> cr.Color = new Cairo.Color(1, 1, 1, 0);
> cr.Operator = Operator.Over;
> RenderCairo(new RenderContext(cr,
> This happens every render cycle and then the image data from the surface
> gets copied to an OpenGL texture and rendered to the screen. So, there's no
> direct Gtk# involved, but I run it inside a Gtk# app on Linux and a WPF app
> on Windows (both using the Tao OpenGL bindings).
> The access violations seem to happen randomly, but generally within a couple
> seconds of interacting with the app. It happens on either the cr.Paint()
> call or one of the cr.Operator calls.
> One thing that I had to change to get it to compile on Windows is adding a
> ref to the image data argument in the ImageSurface constructor. It compiles
> and runs fine without it on Linux, but not on Windows. I'm not even sure how
> this could be as I'm using the same version of Mono.Cairo (2.0.0).
> Anyway, I'm at a bit of a loss as to how to debug this issue. Obviously some
> memory (the image data buffer?) is being moved or freed unintentionally and
> then accessed later, but I just don't see why that would be, especially
> since it works wonderfully on Linux. Any help would be appreciated.
The "ref" version of the ctor is obsolete:
Because the obsoleted version does nothing, that means that the
ImageSurface's "surface" pointer is zero, so code that dereferences it
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