A puzzle from DXSDK

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"The perspective transform converts a viewing frustum into a new coordinate space. Notice that the frustum becomes cuboid and also that the origin moves from the upper-right corner of the scene to the center." ---From DXSDK Its obvious that after perspective transform, the view frustrum becomes cuboid. but the origin is at the upper-right corner of the scene? when? I know that ive got some misunderstanding here. who can give me a clue? Who to read the whole article? thy this link: http://msdn2.microsoft.com/en-us/library/bb147302.aspx

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This seems like an error in the documentation. The scene does get shifted from -1...1 to 0...viewport height and width, but this happens automatically after the perspective transform (fixed function vertex pipeline) or vertex shader (programmable vertex pipeline), and before pixel shader or combiner.

An ordinary perspective transform doesn't usually specify translations in xy plane. An exception to this is if you actually want to shift the perspective center around.