Updated crt-pi shader

GreenHawk84 · 16 Aug 2016, 01:03

@caver01, I run RetroPie on a 1920x1080 screen, I havent played with resolution on anything. Is there a difference enabling high resolutions vs. whatever RetroPie renders at default? Do you recommend anything for a 1920x1080 screen? And if so, where do I go in RetroPie to start messing with resolutions?

caver01 · 16 Aug 2016, 18:12

@GreenHawk84 A while back, the default emulator resolution was changed in RetroPie such that the cores now render in the resolution you are running on your Pi. There was a lot of discussion on the topic related to how this would affect performance, but in the long run, I think it was a good decision. You can always drop it down using runcommand. I recommend experimenting with that a bit so you know what affect it has on your setup.

For example, I run everything I can at 1280x1024, but it can be interesting to see what happens if I specify 640x480 using runcommand. This may improve performance, as many games might run in that resolution (or lower) anyway, but it forces my LCD to upscale the image to fill the screen. This is fine for some folks and ideal for anyone that is building portables around small screens, but it effectively hands the scaling process over to your display.

Those of us who run HD (or near HD) displays who want to reproduce the CRT look will be unhappy with LCD scaling. It s better to run at the native resolution of the display so you can get the most out of shaders. Shaders can leverage the extra pixels to simulate RGB triads and shadow masks. That does come with a potential performance compromise, but if the magnification impact is minimal, and if the shaders can be built in a way that combines the least impact with the best effect, running higher resolution makes a lot of sense. @davej is the real expert here, as he built the PI-CRT shader to perform well at 1080P, but as you can see from his description above, memory access constraints can affect performance.

Everyone has their own opinion about it, but I feel that at my resolution (1280x1024) the PI-CRT shaders are amazing on the Pi3, and running this way is why I choose libretro cores whenever possible. Playability of the games is obviously important, but a big part of what puts the "retro" in RetroPie for me comes from the sense of nostalgia that comes from seeing the realistic look and feel which is why I even enable curvature on my setup. So, that means high-res rendering with CRT shaders enabled whenever possible.

The holy grail for me will be the ability to render vector games at a display's native resolution with gorgeous glow/bloom CRT effects--especially on monochrome (no scanlines) games.

senkun · 16 Aug 2016, 18:35

@caver01 said in Updated crt-pi shader:

ideal for anyone that is building portables around small screens, but it effectively hands the scaling process over to your display.

PI-CRT shaders are amazing on the Pi3, and running this way is why I choose libretro cores whenever possible.

Could not agree more!

BuZz · 16 Aug 2016, 18:35

Just to clarify a couple of things:

Changing the screen mode - scaling done by screen
Changing the render resolution (retroarch only) - scaling done by RPI hardware (no performance loss)

By default the render resolution is the same as the video output resolution. You can lower this for all retroarch emulators via the configuration editor, or per system. Via the runcommand launch menu you can further change this on a per emulator or per rom basis.

Video output resolution can be changed via runcommand on a per emulator or per rom basis.

To change video output resolution for everything you can do it via the /boot/config.txt

I run my 1080p screen at 720p for RetroPie, with the crt-pi shader. It's a modern screen and does a better job of scaling than the RPI imho. I also run Kodi, but as Kodi can switch resolution itself, when Kodi loads it switches to 1080p and back to 720p on exit.

GreenHawk84 · 17 Aug 2016, 01:16

@caver01 @BuZz so dumb question.. I didnt change any settings for resolution, just whatever Retropie setup as. So since my monitor is 1080p is that what I am getting with each core?

BuZz · 17 Aug 2016, 01:27

@GreenHawk84 tvservice -s from a terminal will tell you what mode you are in

Riverstorm · 17 Aug 2016, 16:48

@BuZz said in Updated crt-pi shader:

I run my 1080p screen at 720p for RetroPie

tvservice -s from a terminal will tell you what mode you are in

Can you guys clear up some confusion. If you set your TV's output resolution to 720p vs 1080p does the RetroPie try and negotiate an output resolution equal to 720p as that's what the TV will signal back as it's highest possible resolution even though it's capable of higher resolutions?

Then if your render resolution is lower than your TV (output resolution?) the TV up-scales (the TV decides it's method of up-scaling?) or you can adjust your render resolution to something equal or lower? Would you improve performance by setting your render res low and offloading the upscale to the TV or is this where you loose quality or uniqueness?

By default isn't the render resolution generally always lower than the output of modern TV's? So you would need to decide render res (via pi hardware) or output res (via TV) to scale?

If your render resolution is greater than your output then does it clip or down-scale?

Where does the crt-pi shader "layer" in? After the render res but before the output res seems logical?

BuZz · 17 Aug 2016, 16:52

The resolution is set by the connecting device - if you mean if you set the video mode to 720p - that's the mode the RPI will output to the TV. The tv will upscale it if it needs to.

Render resolution is nothing to do with the TV - the RPI will upscale from render resolution to the video output resolution.

by default the render resolution will match whatever the current video mode is. they will be the same.

Riverstorm · 17 Aug 2016, 17:02

@BuZz said in Updated crt-pi shader:

The resolution is set by the connecting device - if you mean if you set the video mode to 720p - that's the mode the RPI will output to the TV. The tv will upscale it if it needs to.

Sorry Buzz if this is a completely dumb question as I am still missing it. If the TV is set to 720p and the Pi receives a signal from the TV saying output in this mode (this is the output res?) if they match what is there to upscale?

Render resolution is nothing to do with the TV - the RPI will upscale from render resolution to the video output resolution.

So render res is coming from the emulator and the pi is the middle layer sort-to-speak that adjusts the render res to match the output res?

BuZz · 17 Aug 2016, 17:37

RPI looks at the EDID information the tv provides and chooses the mode the TV says is recommended. Some TV's give the wrong information (bad firmware etc). RPI will choose the resolution the TV wants in most cases (which would normally be the native resolution).

The render res is a retroarch feature. the retroarch code uses the dispmanx api to scale from render res to video output res.

BuZz · 17 Aug 2016, 17:39

I have a screen downstairs that has a native resolution of 1024x768. However by default a 720p mode is used, as this is the preferred mode in the EDID info. It of course looks wrong. In this case I manually via /boot/config.txt set the screen to 1024x768 @60hz and then it looks correct.

Riverstorm · 17 Aug 2016, 18:14

Thanks Buzz I think I have it straight, I think I just need to ponder on it a little. Can I try and apply it to a real scenario with default settings. A games "native" resolution let's say for example is 320x200. Retroarch would upscale it to 640x400 (the default res is 640x480 but it would fill it in vertically but horizontally it would have 40 blank pixels on either side?) From there it would be further upscaled at/to the TV's res (for example 720p which is 1280x720) with some fractional integer. I know I will need to keep reading and asking before it all comes full circle but I don't want to completely muddy this thread.

caver01 · 17 Aug 2016, 18:26

@Riverstorm There is one more step that may apply--your TV's native pixels may not be 1280x720 but rather 1920x1080, so unless you see black borders when your TV is set to 720p, your TV is upscaling to its native resolution at the end.

Riverstorm · 17 Aug 2016, 18:44

@caver01 said in Updated crt-pi shader:

@Riverstorm There is one more step that may apply--your TV's native pixels may not be 1280x720 but rather 1920x1080, so unless you see black borders when your TV is set to 720p, your TV is upscaling to its native resolution at the end.

Thanks Caver, I didn't think of that at all. A 720p setting on a native 1080p TV would leave a border all the way around unless the pixels stretch? I am guessing if no scaling happened you would have a small 320x200 square in the middle of the screen. So many factors in there including more like integer scaling, etc. I was hoping to grasp just the general steps a game goes through from start (emulator) to finish (TV) but I don't think I quite have a good understanding. Hopefully with time.

caver01 · 17 Aug 2016, 20:14

@Riverstorm Actually, by your descriptions I think you do have a good understanding. I don't expect anyone who runs their TV in 720 mode has black borders. That was just to make a point that the TV mode is really just another level of scaling. As Buzz said earlier, he actually likes the way his TV scales from 720.

What helps me is to work backwards from the native pixels and decide if I like each step. Assuming I can correctly account for what is doing the scaling, it helps me recognize opportunities. For example, because I know the shader can handle it, I want to give retroarch a resolution as close as I can to native pixels so that these can be used by the shader to create better CRT effects. So, I run at my LCD's full resolution, letting the emulator fill this and giving the shader the most pixels for creating smooth scanlines and curvature effects. Buzz, on the other hand, sounds like he drops his down to 720. He's still getting good effects at that resolution, but he likes how his display upscales beyond that. In fact, anyone with UltraHD is in the same boat, as they are not likely running their Pi at 3840x2160, but something lower and letting their TV upscale.

Riverstorm · 17 Aug 2016, 21:52

@caver01 said in Updated crt-pi shader:

Buzz, on the other hand, sounds like he drops his down to 720

I appreciate you explaining it. I still feel like I am missing pieces. When you wrote the line above. Where would he be dropping it down to 720p? You change the screen mode reported/sent to the Pi and it thinks the display is a 720p which makes Retroarch render at 720p but the TV itself will upscale to the native res of 1080p?

I want to give retroarch a resolution as close as I can to native pixels so that these can be used by the shader to create better CRT effects

I prefer this but on the other hand if you allow the TV to upscale in theory it seems it should be a huge performance boost if the resolution is low enough as the Pi doesn't need to do any additional "resolution rendering" work and the TV is taking the load and doing the upscaling ? But when I think like that it contradicts what Buzz wrote which means I am not understanding it.

Changing the render resolution (retroarch only) - scaling done by RPI hardware (no performance loss)

If I am to far off base you can let me know and I am ok enjoying RetroPie if not completely understanding the logic. :)

BuZz · 17 Aug 2016, 22:29

I appreciate you explaining it. I still feel like I am missing pieces. When you wrote the line above. Where would he be dropping it down to 720p? You change the screen mode reported/sent to the Pi and it thinks the display is a 720p which makes Retroarch render at 720p but the TV itself will upscale to the native res of 1080p?

You don't change the screenmode on the TV. You change it on the RPI. In my case, the TV still says to the RPI - "I prefer 1080p". I then configure the RPI via /boot/config.txt to switch to 720p. - the TV will then deal with that signal and upscale it etc.

GreenHawk84 · 17 Aug 2016, 22:33

@BuZz said in Updated crt-pi shader:

@GreenHawk84 tvservice -s from a terminal will tell you what mode you are in

Thanks BuZz, I did this. It shows me "state 0x12000a [HDMI CEA (16) RGB lim 16:9], 1920x1080 @60.00Hz, progressive"

So this is also what all of my cores do?

BuZz · 17 Aug 2016, 22:56

@GreenHawk84 That is the video mode you are in, unless you have changed it on a per system or rom basis.

Your cores render to whatever the "render resolution" is set to - which by default is the same as the video mode on a RPI2 image, unless you have changed it, or come from an old version of retropie when we had a 640x480 render resolution default. On the RPI1 the render resolution is set to 640x480 for performance reasons.

Riverstorm · 18 Aug 2016, 14:46

@BuZz said in Updated crt-pi shader:

You don't change the screenmode on the TV. You change it on the RPI. In my case, the TV still says to the RPI - "I prefer 1080p". I then configure the RPI via /boot/config.txt to switch to 720p. - the TV will then deal with that signal and upscale it etc.

That clears up a few things for sure on my misconception of how the TV talks to the Pi! :) So the output res hasn't nothing to do with the TV for the most part.

To try again. You start with a low res game like something that's 320x200 that use integer scaling or some other method to upscale the original games resolution to fit the render res, then it's passed up to the output res, that finally the frame passes to the TV that might further scale the image?

If you start with a render res that is lower than the output res does it upscale to fit the output res before passing to the TV or would you have a border or something?