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Crafter

A question about D3DDECLUSAGE

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Crafter    122
There's a paragraph explains D3DDECLUSAGE_POSITION : ------------------------------------------------------------ Position data ranging from (-1,-1) to (1,1). Use D3DDECLUSAGE_POSITION with a usage index of 0 to specify untransformed position for fixed function vertex processing and the n-patch tessellator. Use D3DDECLUSAGE_POSITION with a usage index of 1 to specify untransformed position in the fixed function vertex shader for vertex tweening. ---------------------------------------------------------------------- In DirectX SDK (August 2007) what's the meaning of "Position data ranging from (-1,-1) to (1,1). " ? is the position data in World coordinate? and is it a 3D vector? how could it range from (-1,-1) to (1,1) ??

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That description seems entirely wrong. You can use any range of values, and typically, yes, they are 3D. Those limits may apply to usage index 1, when using the n-patch tessellator. I have no idea how that system works.

Positions are usually given in object space, which can be moved to world space with the world matrix. This allows you to use the same mesh in multiple locations in the world, or to have the object move without modifying the vertex data.

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