10

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 ?

rmaddy
  • 314,917
  • 42
  • 532
  • 579
zeus
  • 12,173
  • 9
  • 63
  • 184

1 Answers1

23

Metal Coordinate Systems

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

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).. enter image description here

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). enter image description here

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). enter image description here

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.

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.

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.

vallentin
  • 23,478
  • 6
  • 59
  • 81
Hamid Yusifli
  • 9,688
  • 2
  • 24
  • 48
  • What remains confusing is that while these coordinate systems are in the Metal docs so must be correct, why do images show that the origin in the lower left when doing something like you see here: https://stackoverflow.com/questions/55821459/confused-about-thread-position-in-grid ? I would expect the dark black corner to be in the upper left if that is where the origin is. – johnbakers Dec 28 '19 at 13:38