Coordinate system

starman2049 · Post by **starman2049** » Mon Sep 19, 2005 2:52 pm

Sorry for the newbie question, but I could find by searching. What is the coordinate system on PSP. Is it right-handed y-down like in PS2, or what?

0x0001 · Post by **0x0001** » Tue Sep 20, 2005 10:53 am

yes cordinates are x across y down
same as ps2

480 pixels for x
272 for y

RustyFunkNut · Post by **RustyFunkNut** » Mon Sep 26, 2005 5:32 am

It's also worth pointing out that ScePspMatrix4 is transposed with respect to a D3DMATRIX. Caught me out when converting some of my old code across :)

CyberBill · Post by **CyberBill** » Mon Sep 26, 2005 5:48 am

PSP Matrices are directly in line with OpenGL matrices, but yes, D3D matrices have their axis reversed.

starman2049 · Post by **starman2049** » Thu Sep 29, 2005 9:54 am

Thanks for the info all. I am still playing around with getting my existing camera code working. After not making much progress I am trying to get a simplification working first.

If I set my View Matrix up as follows:

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sceGumMatrixMode&#40;GU_VIEW&#41;;
sceGumLoadIdentity&#40;&#41;;

then I get what I expect, the camera at the origin, aligned with the z-axis, and I can see parts of my scene as I would expect.

If I set my View Matrix up as follows:

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ScePspFMatrix4 worldM;
matrix_identity&#40; &#40;float*&#41;&worldM&#41;; // taken from lights.c sample code
sceGuSetMatrix&#40;GU_VIEW, &worldM&#41;;

Then I am not able to see anything but black screen. I am not really sure why these would be different. Does anybody have any ideas? I am wondering if it could be single vs double precision float issues? or maybe sceGuSetMatrix() has a bug in implementation?

Any help is GREATLY appreciated!!

starman2049 · Post by **starman2049** » Thu Sep 29, 2005 10:26 am

Ok, so after taking a different approach I see that I can use:

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sceGumMatrixMode&#40;GU_VIEW&#41;;
sceGumLoadMatrix&#40;&worldM&#41;;

Which seems to work better. I don't know why

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sceGuSetMatrix&#40;GU_VIEW, &worldM&#41;;

doesn't work right, but I am off and running again...

chp · Post by **chp** » Thu Sep 29, 2005 5:45 pm

the GUM library uses sceGuSetMatrix() internally, so I doubt that's what at fault. Are you using sceGum* methods to draw aswell? In that case perhaps you have dirty data in the view-matrix that gets flushed when you render.

Paco · Post by **Paco** » Tue Oct 11, 2005 9:22 am

For what is worth, I'm using my old left-handed matrix code (from D3D engine) on the PSP successfully, zero changes were needed. X to the right, Y up, Z into the screen, which IIRC was the way D3D wanted it for W-Buffering.

Different coordinate systems suck.