Metal Support Thread

[jcm93]

Original Title: Metal Shader Compatibility Report (via ares emulator)

Native Metal support was recently added to ares to complement its librashader support. I've started to do some testing with a bunch of shaders and wanted to start reporting preliminary findings from the .slangp shader library it bundles.

Overall impressions are great. Most things seem to be working correctly and performing well.

I don't have a reference for how these shaders behave on other platforms, so I can mostly only point out things that seem 'obviously broken,' or else obvious things like compiler failures.

With that said, here's a preliminary list so far. I expect to eventually test everything, this is just from my first round of tests, to start getting stuff out there.

Last updated 9/18:

Loads fine, incorrect output

crt/crt-geom-deluxe.slangp fixed
crt/crt-slangtest-cubic.slangp fixed
crt/crt-slangtest-lanczos.slangp fixed
presets/crt-royale-smooth.slangp blurring issue fixed
bezel/Mega_Bezel/Presets/MBZ__0__SMOOTH-ADV.slangp blurring issue fixed
test/history.slangp - stuttering seems to be intended

Filter chain creation failure

vhs/VHSPro.slangp

misc/print-resolution.slangp fixed
misc/patchy-color.slangp fixed
bfi/120hz-smart-BFI.slangp fixed
test/pragma-name.slangp fixed
crt/crt-guest-advanced-ntsc.slangp fixed
vhs/mudlord-pal-vhs.slangp fixed, was broken shader
test/feedback-noncausal.slangp intended broken
sharpen/Anime4k.slangp known broken shader

Other

vhs/vhs_and_crt_godot.slangp - Loads, renders, but pegs GPU to 100% even at low resolutions. Could just be a shader issue.

Other notes so far are that "megabezel" shader performance across the board is somewhat poor (i.e. worse than RetroArch) at ~4K resolutions when its reflections are enabled. This may simply be a shader issue but I figured worth including.

For testing, the ares' recent CI builds all include the Metal backend. I can provide more information or Metal GPU captures as well if needed for anything, if that is helpful.

[chyyran]

Filter chain failure is odd, I wonder if it might be something in SPIRV-Cross.. Will take a look this or next week.

[chyyran]

Metal GPU captures would be massively helpful here, as well as LLVM logs from the compiler if you’re able to get them.

[jcm93]

Metal GPU captures would be massively helpful here, as well as LLVM logs from the compiler if you’re able to get them.

Sure, I'll get captures from the ones that appear to be rendering nothing; can you provide any guidance on the latter point? Is there a way to get the compiler output to appear in stdout for example? Would compiling librashader in debug mode do the job? I notice that I already get compilation warnings from the shaders by default.

[chyyran]

It should show up in debug logs in Xcode when first loading the shader. It’s not a librashader thing but a Metal -> MetalIR thing

[jcm93]

Hmm, I don't get any output I can see from filter chain creation, even with Xcode Metal API and Shader validation enabled. I tried in the objctest code as well; selecting crt-guest-advanced-ntsc just ends up with a nil _filterChain. I see a couple compilation warnings, but compilation succeeds.

[chyyran]

Thats fine, I’ll investigate crt-guest-advanced-ntsc on my end.

[jcm93]

Here are the GPU captures. They should be labeled appropriately. Let me know if you have any issues opening or getting relevant data from them!

https://drive.google.com/file/d/11bNWB78_drEg1IW3t4ZcViupYgg8qQkd/view?usp=sharing

For the vhs shader capture, it seemed to peg my GPU above a certain resolution, so I notched it just above that and took a capture. Again, that one could just be a shader issue, but I figured it was worth including. I also included a megabezel capture; it seems to be doing some very weird stuff indeed (frame times there were exceedingly high every few frames, though not every frame, so looking at this more closely, I think it's just dropping frames; regardless, I included three frames in that capture); I couldn't exactly tell what was going on.

[chyyran]

mudlord-pal is a known broken shader: https://github.com/SnowflakePowered/librashader/actions/runs/8577373017/job/23509866495#step:4:376

seems like crt-guest-advanced has been failing, will need to double check but it smells like a shader issue.

[chyyran]

Anime4k is also a known broken shader

[jcm93]

Testing some things in ares and noticed another librashader issue with certain 'smoothing' shaders such as presets/crt-royale-smooth.slangp or bezel/Mega_Bezel/Presets/MBZ__0__SMOOTH-ADV.slangp.

Left librashader, right RetroArch:

Screenshots are of the megabezel shader; here is a gputrace from the crt-royale-smooth shader which exhibits similar behavior.

https://drive.google.com/file/d/1NBePGt62XmFZ_mthqlR8YTj8EC7EFVdG/view?usp=share_link

[chyyran]

I think the smoothing behaviour probably has to do with how mipmaps are handled. I won't have a shot at debugging this until a few weeks from now, sorry for the extended wait.

[jcm93]

No worries! Nothing critical. I haven't finished testing either and it's possible there are upstream updates to some of the ones in this thread, I'll just keep adding reports and keeping the OP updated when time allows for me as well.

[chyyran]

Seems like test/history.slangp is horribly broken for some reason.

[chyyran]

22b2118 + e24beed definitively fix crt-geom-deluxe

cebc7a9 fixes history

[chyyran]

• crt-guest-advanced-ntsc seems like a broken shader preset:

ShaderReflectError(FragmentSemanticError(UnknownSemantics("PrePass0")))

• feedback-noncausal is a test shader that is intended to be broken.

• VHSPro is interesting..

  called `Result::unwrap()` on an `Err` value: MetalError(NSError { domain: "MTLLibraryErrorDomain", code: 3, user_info: {"NSLocalizedDescription": <__NSCFString: 0x1510fe800>} })
  

[chyyran]

VHSPro compiler error

program_source:171:22: error: call to 'fmod' is ambiguous
    return fract(sin(fmod(param, param_1)) * 43758.546875);
                     ^~~~
/System/Library/PrivateFrameworks/GPUCompiler.framework/Versions/32023/Libraries/lib/clang/32023.196/include/metal/metal_math:4661:18: note: candidate function
METAL_FUNC float fmod(float x, float y)
                 ^
program_source:153:7: note: candidate function
float fmod(thread const float& a, thread const float& b)
      ^
program_source:192:30: error: call to 'fmod' is ambiguous
    float c = n * smoothstep(fmod(param_2, param_3), 0.0, 0.949999988079071044921875);
                             ^~~~
/System/Library/PrivateFrameworks/GPUCompiler.framework/Versions/32023/Libraries/lib/clang/32023.196/include/metal/metal_math:4661:18: note: candidate function
METAL_FUNC float fmod(float x, float y)
                 ^
program_source:153:7: note: candidate function
float fmod(thread const float& a, thread const float& b)
      ^
program_source:206:10: warning: unused variable 'VHS_Bleed' [-Wunused-variable]
    bool VHS_Bleed = global.VHS_Bleed_toggle != 0.0;
         ^
program_source:207:9: warning: unused variable 'VHS_BleedMode' [-Wunused-variable]
    int VHS_BleedMode = int(global.VHS_BleedMode_select);
        ^
program_source:208:10: warning: unused variable 'VHS_FishEye' [-Wunused-variable]
    bool VHS_FishEye = global.VHS_FishEye_toggle != 0.0;
         ^
program_source:209:10: warning: unused variable 'VHS_FishEye_Hyperspace' [-Wunused-variable]
    bool VHS_FishEye_Hyperspace = global.VHS_FishEye_Hyperspace_toggle != 0.0;
         ^
program_source:210:10: warning: unused variable 'VHS_Vignette' [-Wunused-variable]
    bool VHS_Vignette = global.VHS_Vignette_toggle != 0.0;
         ^
program_source:213:10: warning: unused variable 'VHS_YIQNoise' [-Wunused-variable]
    bool VHS_YIQNoise = global.VHS_YIQNoise_toggle != 0.0;
         ^
program_source:214:9: warning: unused variable 'signalNoiseType' [-Wunused-variable]
    int signalNoiseType = int(global.signalNoiseType_select);
        ^
program_source:217:10: warning: unused variable 'VHS_ScanLines' [-Wunused-variable]
    bool VHS_ScanLines = global.VHS_ScanLines_toggle != 0.0;
         ^
program_source:218:10: warning: unused variable 'VHS_LinesFloat' [-Wunused-variable]
    bool VHS_LinesFloat = global.VHS_LinesFloat_toggle != 0.0;
         ^
program_source:219:10: warning: unused variable 'VHS_Stretch' [-Wunused-variable]
    bool VHS_Stretch = global.VHS_Stretch_toggle != 0.0;
         ^
program_source:220:10: warning: unused variable 'VHS_Jitter_H' [-Wunused-variable]
    bool VHS_Jitter_H = global.VHS_Jitter_H_toggle != 0.0;
         ^
program_source:221:10: warning: unused variable 'VHS_Jitter_V' [-Wunused-variable]
    bool VHS_Jitter_V = global.VHSJitter_V_toggle != 0.0;
         ^
program_source:222:10: warning: unused variable 'VHS_Twitch_H' [-Wunused-variable]
    bool VHS_Twitch_H = global.VHS_Twitch_H_toggle != 0.0;
         ^
program_source:223:10: warning: unused variable 'VHS_Twitch_V' [-Wunused-variable]
    bool VHS_Twitch_V = global.VHS_Twitch_V_toggle != 0.0;
         ^
program_source:224:10: warning: unused variable 'VHS_SignalTweak' [-Wunused-variable]
    bool VHS_SignalTweak = global.VHS_SignalTweak_toggle != 0.0;
         ^
program_source:225:10: warning: unused variable 'VHS_Feedback' [-Wunused-variable]
    bool VHS_Feedback = global.VHS_Feedback_toggle != 0.0;
         ^
program_source:226:12: warning: unused variable 'feedbackColor' [-Wunused-variable]
    float3 feedbackColor = float3(global.feedbackColor_R, global.feedbackColor_G, global.feedbackColor_B);
           ^
program_source:227:10: warning: unused variable 'feedbackDebug' [-Wunused-variable]
    bool feedbackDebug = global.feedbackDebug_toggle != 0.0;
         ^

program_source:123:12: error: call to 'fmod' is ambiguous
    uv.y = fmod(param_4, param_5);
           ^~~~
/System/Library/PrivateFrameworks/GPUCompiler.framework/Versions/32023/Libraries/lib/clang/32023.196/include/metal/metal_math:4661:18: note: candidate function
METAL_FUNC float fmod(float x, float y)
                 ^
program_source:99:7: note: candidate function
float fmod(thread const float& a, thread const float& b)
      ^
program_source:138:150: error: call to 'fmod' is ambiguous
    uv.x += ((((sin((uv.y * 10.0) + t) / 250.0) * onOff(param, param_1, param_2, param_3)) * (1.0 + cos(t * 80.0))) * (1.0 / (1.0 + ((20.0 * (uv.y - fmod(param_4, param_5))) * (uv.y - fmod(param_6, param_7))))));
                                                                                                                                                     ^~~~
/System/Library/PrivateFrameworks/GPUCompiler.framework/Versions/32023/Libraries/lib/clang/32023.196/include/metal/metal_math:4661:18: note: candidate function
METAL_FUNC float fmod(float x, float y)
                 ^
program_source:99:7: note: candidate function
float fmod(thread const float& a, thread const float& b)
      ^
program_source:138:185: error: call to 'fmod' is ambiguous
    uv.x += ((((sin((uv.y * 10.0) + t) / 250.0) * onOff(param, param_1, param_2, param_3)) * (1.0 + cos(t * 80.0))) * (1.0 / (1.0 + ((20.0 * (uv.y - fmod(param_4, param_5))) * (uv.y - fmod(param_6, param_7))))));
                                                                                                                                                                                        ^~~~
/System/Library/PrivateFrameworks/GPUCompiler.framework/Versions/32023/Libraries/lib/clang/32023.196/include/metal/metal_math:4661:18: note: candidate function
METAL_FUNC float fmod(float x, float y)
                 ^
program_source:99:7: note: candidate function
float fmod(thread const float& a, thread const float& b)
      ^
program_source:155:21: error: call to 'fmod' is ambiguous
    float t2 = tt - fmod(param, param_1);
                    ^~~~
/System/Library/PrivateFrameworks/GPUCompiler.framework/Versions/32023/Libraries/lib/clang/32023.196/include/metal/metal_math:4661:18: note: candidate function
METAL_FUNC float fmod(float x, float y)
                 ^
program_source:99:7: note: candidate function
float fmod(thread const float& a, thread const float& b)
      ^
program_source:170:24: error: call to 'fmod' is ambiguous
    float sh2 = 1.0 - (fmod(param_8, param_9) / w);
                       ^~~~
/System/Library/PrivateFrameworks/GPUCompiler.framework/Versions/32023/Libraries/lib/clang/32023.196/include/metal/metal_math:4661:18: note: candidate function
METAL_FUNC float fmod(float x, float y)
                 ^
program_source:99:7: note: candidate function
float fmod(thread const float& a, thread const float& b)
      ^
program_source:194:22: error: call to 'fmod' is ambiguous
    return fract(sin(fmod(param, param_1)) * 43758.546875);
                     ^~~~
/System/Library/PrivateFrameworks/GPUCompiler.framework/Versions/32023/Libraries/lib/clang/32023.196/include/metal/metal_math:4661:18: note: candidate function
METAL_FUNC float fmod(float x, float y)
                 ^
program_source:99:7: note: candidate function
float fmod(thread const float& a, thread const float& b)
      ^
program_source:365:13: error: call to 'fmod' is ambiguous
        if (fmod(param_24, param_25) < 1.0)
            ^~~~
/System/Library/PrivateFrameworks/GPUCompiler.framework/Versions/32023/Libraries/lib/clang/32023.196/include/metal/metal_math:4661:18: note: candidate function
METAL_FUNC float fmod(float x, float y)
                 ^
program_source:99:7: note: candidate function
float fmod(thread const float& a, thread const float& b)
      ^
program_source:489:19: warning: unused variable 'tnl_1' [-Wunused-variable]
            float tnl_1 = tape.sample(tapeSmplr, pn).y;
                  ^

[chyyran]

#125 should fix crt-guest-advanced-ntsc and crt-slangtest-*

[chyyran]

#127 fixes

• misc/print-resolution.slangp
• bfi/120hz-smart-BFI.slangp
• test/pragma-name.slangp

VHSPro seems to be an issue with the SPIRV-Cross output. I will file a ticket upstream to see if we can get it fixed.

patchy-color is a shader problem upstream, this is the output from D3D11 but I assume there are similar issues with Metal

Shader@0x0000013690D34FD0(211,18-30): error X3507: 'testPattern': Not all control paths return a value

[chyyran]

patchy-color was fixed upstream

[jcm93]

Updated OP; could not find any further filter chain creation failures or obviously incorrect outputs. Testing not totally exhaustive yet but fairly broad. Thanks for all the fixes!

[chyyran]

KhronosGroup/SPIRV-Cross#2382 this should hopefully fix VHSPro (after bumping spirv-cross-sys)

[chyyran]

spirv-cross-sys was updated and should fix VHSPro. This won't automatically backport to 0.4.x but if librashader-capi is rebuilt it'll pull in the new version of the sys crate.

[chyyran]

Converting this issue to a discussion until there are more concrete examples of shader failures on Metal.