Sprite sheets

A sprite sheet is one big image with several frames of the same sprite on it. For example, you can save this animation:

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Like an horizontal sprite sheet:

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A vertical one:

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Or a matrix:

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Import

To import a sprite sheet use File > Import Sprite Sheet option. Then you can select:

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Export

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Automate from Command Line

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Texture Atlases

A texture atlas is an huge image with all the graphics, sprites and images that a game will use. It's called "texture" because the image can be loaded into the video memory, to render graphics on screen with hardware acceleration.