What is the coordinate system used in metal?

Question

In metal what coordinate system to use inside shader (in and out)? and when we render to texture is it the same? with the z buffer also? Are there any inconsistencies? finally what are the difference between metal, opengl and directX ?

Answer 1

Metal Coordinate Systems

Metal defines several standard coordinate systems to represent transformed graphics data at different stages along the rendering pipeline.

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1) NDC (Normalized Device Coordinate): this coordinates is used by developers to construct their geometries and transform the geometries in vertex shader via model and view matrices.
Point(-1, -1) in NDC is located at the the bottom left corner (Y up)..

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2) Framebuffer Coordinate (Viewport coordinate): when we write into attachment or read from attachment or copy/blit between attachments, we use framebuffer coordiante to specify the location. The origin(0, 0) is located at the top-left corner (Y down).

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3) Texture Coordinate: when we upload texture into memory or sample from texture, we use texture coordinate. The origin(0, 0) is located at the top-left corner (Y down).

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D3D12 and Metal

NDC: +Y is up. Point(-1, -1) is at the bottom left corner.
Framebuffer coordinate: +Y is down. Origin(0, 0) is at the top left corner.
Texture coordinate: +Y is down. Origin(0, 0) is at the top left corner.

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OpenGL, OpenGL ES and WebGL

NDC: +Y is up. Point(-1, -1) is at the bottom left corner.
Framebuffer coordinate: +Y is up. Origin(0, 0) is at the bottom left corner.
Texture coordinate: +Y is up. Origin(0, 0) is at the bottom left corner.

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Vulkan

NDC: +Y is down. Point(-1, -1) is at the top left corner.
Framebuffer coordinate: +Y is down. Origin(0, 0) is at the bottom left corner.
Texture coordinate: +Y is up. Origin(0, 0) is at the bottom left corner.

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