Class TImagesCache

Unit

ImagesCache

Declaration

type TImagesCache = class(TObject)

Description

A cache of loaded images.

The idea is that instead of Image := LoadImage(...) call Image := Cache.LoadImage_IncReference(...). Later, instead of freeing this image, call LoadImage_DecReference(Image). From your point of view, things will work the same. But if you expect to load many images from the same FileName, then you will get a great speed and memory saving, because image will only be actually loaded once. Notes:

• All passed here FileNames must be absolute, already expanded paths. In the future it's expected that this (just like LoadImage, actually) will be extended to load images from URLs.

• Note that in case of problems with loading, LoadImage_IncReference may raise an exception, just like normal LoadImage. In this case it's guaranteed that no reference will be incremented, of course. If LoadImage_IncReference returns in a normal way, then it will return something non-Nil, just like LoadImage does.

• For now, LoadImage is always called with AllowedImageClasses = [TRGBImage, TAlphaImage] and ForbiddenConvs = []. Why ? Because this is the use case that I need right now... (I'm going to use this for VRML texture nodes.) This will be fixed (LoadImage_IncReference will get AllowedImageClasses and ForbiddenConvs parameters, will compare and save them in TImageCache record) as soon as the need will arise.

• LoadImage_DecReference alwas sets Image to Nil, like FreeAndNil.

Note that before destroying this object you must free all images, i.e. call LoadImage_DecReference for all images allocated by LoadImage_IncReference. This class is not a lousy way of avoiding memory leaks — it would be a bad idea, because it would cause sloppy programming, where memory is unnecessarily allocated for a long time. In fact, this class asserts in destructor that no images are in cache anymore, so if you compiled with assertions enabled, this class does the job of memory-leak detector.

Hierarchy

• TObject
• TImagesCache

Overview

Methods

	constructor Create;
	destructor Destroy; override;
	function LoadImage_IncReference(const FileName: string): TImage;
	procedure LoadImage_DecReference(var Image: TImage);

Description

Methods

	constructor Create;

	destructor Destroy; override;

	function LoadImage_IncReference(const FileName: string): TImage;

	procedure LoadImage_DecReference(var Image: TImage);