GetCanvasDc Cleanup

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jpbro Members Profile Find Members Posts Senior Member Joined: 29 Mar 11 Status: Offline Points: 77	Post Options Post Reply Quote jpbro Report Post Thanks(0) Quote Reply Topic: GetCanvasDc Cleanup Posted: 14 Oct 11 at 10:13PM
	After getting a DC handle with GetCanvasDC, do we have to call DeleteDC to cleanup, or does LoadFromCanvasDC handle cleanup? What if we call GetCanvasDc but for some reason, we do not subsequently call LoadFromCavasDc - would we have to call DeleteDC then? This is for Qpdf 7.26. Thanks for any clarifications.

AndrewC Members Profile Find Members Posts Moderator Group Joined: 08 Dec 10 Location: Geelong, Aust Status: Offline Points: 841	Post Options Post Reply Quote AndrewC Report Post Thanks(0) Quote Reply Posted: 17 Oct 11 at 3:09PM
	Looking at the QPL source code I see that a TMetaFile is actually created with the GetCanvasDC function and the DC from the Metafile is the return value. This TMetafile class is only released when LoadFromCanvasDC is called which then releases the DC. It looks like these two calls must me called in pairs, GetCanvasDC to create the MetaFile and then cleanly release it when finished.

jpbro Members Profile Find Members Posts Senior Member Joined: 29 Mar 11 Status: Offline Points: 77	Post Options Post Reply Quote jpbro Report Post Thanks(0) Quote Reply Posted: 17 Oct 11 at 10:07PM
	Thanks a lot Andrew, I will make sure that LoadFromCanvasDC is called in my Class_Terminate event if I've previously called GetCanvasDC to ensure proper cleanup.

jpbro Members Profile Find Members Posts Senior Member Joined: 29 Mar 11 Status: Offline Points: 77	Post Options Post Reply Quote jpbro Report Post Thanks(0) Quote Reply Posted: 09 Nov 11 at 11:42PM
	What about after calling CapturePage? Do we need to cleanup by calling anything? The document doesn't say, but I'm trying to track some memory leaks in my software, so I'm investigating every possibility (BTW, I'm using QPDF 7.26) Thanks for any advice.

jpbro Members Profile Find Members Posts Senior Member Joined: 29 Mar 11 Status: Offline Points: 77	Post Options Post Reply Quote jpbro Report Post Thanks(0) Quote Reply Posted: 30 Nov 11 at 2:02PM
	Hi Andrew - any chance you could get back to me on this? Is there any cleanup required after calling CapturePage, or does calling DrawCapturedPage release the capture page handle?

AndrewC Members Profile Find Members Posts Moderator Group Joined: 08 Dec 10 Location: Geelong, Aust Status: Offline Points: 841	Post Options Post Reply Quote AndrewC Report Post Thanks(0) Quote Reply Posted: 08 Dec 11 at 1:10AM
	As stated earlier these two calls need to be paired. ie. Call one then the other and then the resources should be freed automatically. If you only call CapturePage then there may be some memory that is not freed until the program is closed. Andrew.

jpbro Members Profile Find Members Posts Senior Member Joined: 29 Mar 11 Status: Offline Points: 77	Post Options Post Reply Quote jpbro Report Post Thanks(0) Quote Reply Posted: 08 Dec 11 at 3:16PM
	Great, thanks for the information Andrew.

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