The SpriteFrame documentation mentions this several times. For example,
create()
Create a SpriteFrame with a texture filename, rect in points. It is assumed that the frame was not trimmed.
getOriginalSizeInPixels(void)
get original size of the trimmed image
What does it mean?
In particular, if I created a spritesheet with TexturePacker from a bunch of images, and then loaded it by calling SpriteFrameCache::getInstance()->addSpriteFramesWithFile(“Images.plist”), will getOriginalSizeInPixels() give me the original size of the corresponding image, or some other (smaller?) number depending on how it decided to trim the image?
TexturePacker allows trimming the excess whitespace around the individual image files.
Check see visual example of “Trimming / Cropping” section of https://www.codeandweb.com/texturepacker
Basically if your sprite frames are, for example, 100x100 .png images, and TexturePacker trims them down to a 60x40 size then _originalSize is 100x100 and _rect is {Vec2_offset, 60x40}.
Cocos2d uses the original size in various cases in order to calculate the vertex coordinates offset, among possibly other values, of the given sprite.
If you want o know further detail consider reading through CCSprite.cpp with a note on methods setSpriteFrame, setVertexCoords, updateStretchFactor (if QUAD block).
