glsl: reduce geometry shader complexity

[gregory38]

output 1 strip of 2 triangles instead of 2 strips of 1 triangle.

Potentially it would reduce the geometry shader overhead. And it
might avoid a middle line in sprite in some AMD GPU/driver/OS
bad combination

Need a quick test on various driver, AMD, Nvidia, Intel.

[lightningterror]

Wish I could test this now but i can't on both intel and amd. eta 2 weeks maybe.
I'd like this to be added before 1.6 release. More fps is always welcome :)

@Sarania can you do some tests?

[MrCK1]

Works fine for me on Nvidia.

[lightningterror]

@MrCK1 can you do some benchmarks?

[MrCK1]

I can, but not until tonight.

[gregory38]

Don't expect too much. First of all, Opengl barely uses geometry shader. And compiler might already do the job correctly. Hum I will check the shader size with Nouveau.

[gregory38]

Here some stats on Nouveau compiler. GPR is the number of used register (less register means more shader run in //). Inst is the number of instruction (less instruction means faster shader run). bytes is the size of the shader. First shader is to convert sprite. And the next 2 are used in the unscale line/point hack.

Before

T:Oth		S:	=> type: 2, local: 0, gpr: 34, inst: 187, bytes: 1712
T:Oth		S:	=> type: 2, local: 0, gpr: 29, inst: 197, bytes: 1808
T:Oth		S:	=> type: 2, local: 0, gpr: 44, inst: 211, bytes: 1936

After

T:Oth		S:	=> type: 2, local: 0, gpr: 37, inst: 133, bytes: 1216
T:Oth		S:	=> type: 2, local: 0, gpr: 30, inst: 142, bytes: 1304
T:Oth		S:	=> type: 2, local: 0, gpr: 33, inst: 147, bytes: 1344

[mirh]

avoid a middle line in sprite

Wait, like in the actual finished rendered image I might see some improvement?
I could give a check to it tomorrow then

[gregory38]

I remembered someone posted some screenshot on an AMG GPU that show sprite diagonal (border of 2 triangles). Normally rasterization rules are obvious. Only a single fragment must be generated at the border. I don't know if it was due to the 2 sprites or a random bug in the driver. Anyway, code is better this way. And maybe someone could do the same for latest added shader.

[gregory38]

Anyone to test Nemo ? @prafullpcsx2 I think you have the game, isn't it.

[prafullpcsx2]

This doesn't show any difference with Nemo. I guess you meant #1994 ? That one surely fixes the Nemo regression.

[lightningterror]

Looks like greg posted in the wrong thread again :D
Anyway yea he meant that one.

[gregory38]

Ah yes. I'm useless