Implement adaptive exposure #1559

VReaperV · 2025-02-21T21:22:06Z

Requires #1550 and #1558
Implements #29

This builds up on #1550 by adding automatic exposure based on scene brightness.

When r_tonemapAdaptiveExposure is enabled, a compute shader gets the geometric mean of luminance before tonemapping. Then in the tonemapper this value is mapped to a curve with coefficients chosen to try to avoid sudden changes and too high/too low exposure values, and multiplied with the HDR colour.

An example of this in practice: https://users.unvanquished.net/~reaper/adaptiveLighting/adaptiveLightingGlobal.mp4

Also moved the material stuff from common_cp to material_cp. This wasn't an issue prior because only the material system used compute shaders, but now this would result in shaders failing to compile if r_materialSystem is disabled (and using macros would result in unnecessary shader re-compilations).

VReaperV · 2025-02-21T21:26:07Z

I'll see if I can add a non-compute path later. The compute one can also easily give histogram information for Unvanquished/Unvanquished#221.

VReaperV · 2025-02-24T17:11:44Z

I've put some of these changes into #1563 to make this pr lighter.

slipher · 2025-03-03T08:06:15Z

That's a good idea. I just tested and it doesn't seem to work as expected: there are large, sudden exposure changes despite very little change in the scene. For example:

VReaperV · 2025-03-03T10:12:40Z

Hmm, I might've broken something with the more recent push, the changes were pretty mild when I was testing it.

VReaperV · 2025-03-10T18:44:40Z

Rebased + fixed some issues. That should hopefully fix the drastic exposure changes as seen on the above screenshot too.

sweet235 · 2025-03-14T20:43:09Z

LGTM

slipher · 2025-03-15T06:50:21Z

I found another buggy place with huge exposure changes between spots that look about the same in mxl-school.

slipher

With my laptop's Nvidia card, taking a screenshot goes from no noticeable delay to a 2-second delay when adaptive exposure is enabled.

Any plans to smooth out the exposure changes over time, like how the eye adapts to light maybe? For now the exposure variation seems too large and rapid to be really usable; all world surfaces are flickering when you move.

Doors feel kind of buggy in general. There is often a bright flash when the door is opening. But maybe that's just the same thing as the preceding paragraph.

slipher · 2025-03-15T07:55:51Z

src/engine/renderer/glsl_source/cameraEffects_fp.glsl

+		#if defined(HAVE_ARB_explicit_uniform_location) && defined(HAVE_ARB_shader_atomic_counters)
+			if( u_TonemapAdaptiveExposure ) {
+					const float l = GetAverageLuminance( luminanceU ) - 8;
+					color.rgb *= clamp( 0.18f / exp2( l * 0.8f + 0.1f ), 0.0f, 2.0f );


Probably the lower limit shouldn't be allowed to go 0

It won't, the lowest it can go is ~0.0016.

VReaperV · 2025-03-15T08:04:17Z

I found another buggy place with huge exposure changes between spots that look about the same in mxl-school.

I miscalculated the max value for luminosity sum, so it does overflow sometimes. Will add a fix later.

slipher · 2025-03-15T08:06:17Z

Also the instant exposure adjustments mess up other effects that are supposed to cause rapid changes in brightness. The flickering of the firelight in metro-b1-2 alien base is almost not visible at all, being canceled out by exposure changes. When a human weapon is fired, the whole scene perversely darkens due to the luminance of the muzzle flash.

VReaperV · 2025-03-15T08:11:30Z

With my laptop's Nvidia card, taking a screenshot goes from no noticeable delay to a 2-second delay when adaptive exposure is enabled.

Hmm, it might be best to improve the screenshotting in some way. I don't think there's much that can be done with this from the adaptive exposure side.

Any plans to smooth out the exposure changes over time, like how the eye adapts to light maybe? For now the exposure variation seems too large and rapid to be really usable; all world surfaces are flickering when you move.

Yeah, I plan to add some exponential smoothing there.

Doors feel kind of buggy in general. There is often a bright flash when the door is opening. But maybe that's just the same thing as the preceding paragraph.

It might be due to the overflow too.

Also the instant exposure adjustments mess up other effects that are supposed to cause rapid changes in brightness. The flickering of the firelight in metro-b1-2 alien base is almost not visible at all, being canceled out by exposure changes. When a human weapon is fired, the whole scene perversely darkens due to the luminance of the muzzle flash.

Yeah, smoothing it over time should make it better, maybe some value tweaking too.

VReaperV · 2025-03-16T19:39:24Z

I found another buggy place with huge exposure changes between spots that look about the same in mxl-school.

This should be fixed now.

illwieckz · 2025-03-17T14:43:42Z

That looks nice but yes the feature should remain disabled by default until some delay / average on some time is implemented, because of the flicking when moving.

slipher · 2025-03-19T11:20:57Z

src/engine/renderer/gl_shader.h

+		GLUniform4f( shader, "u_TonemapParms2", true ) {
+	}
+
+	void SetUniform_TonemapParms2( vec4_t tonemapParms2 ) {


This could use a more readable interface. Arguments with named float(s) instead of vec4

Perhaps so. I'd just made it as an "extension" to u_TonemapParms that was already there.

slipher · 2025-03-19T11:22:34Z

src/engine/renderer/tr_backend.cpp

+	gl_luminanceReductionShader->SetUniform_ViewWidth( width );
+	gl_luminanceReductionShader->SetUniform_ViewHeight( height );
+	vec4_t parms { log2f( r_toneMappingHDRMax.Get() ) };
+	parms[1] = UINT32_MAX / ( width * height * ( uint32_t( parms[0] ) + 8 ) );


Why is UINT32_MAX used?

That is the maximum value that can be held in an atomic_uint, so it ensures that there will be no overflow.

src/engine/renderer/glsl_source/luminanceReduction_cp.glsl

src/engine/renderer/glsl_source/cameraEffects_fp.glsl

src/engine/renderer/glsl_source/common_cp.glsl

Add a compute shader that will compute the geometric mean of scene luminance, then map it to an exposure curve in the `cameraEffects` shader. This is controlled by `r_tonemapAdaptiveExposure`.

slipher

I get a GLSL compile error if I do set r_arb_shader_atomic_counter_ops 0.

slipher · 2025-04-02T20:46:13Z

src/engine/renderer/glsl_source/luminanceReduction_cp.glsl

+	#if defined(SUBGROUP_ATOMIC)
+		const float luminanceSum = subgroupInclusiveAdd( luminance );
+
+		if( subgroupElect() ) {


Mixed spaces and tabs here

VReaperV added T-Improvement Improvement for an existing feature A-Renderer T-Cleanup T-Feature-Request Proposed new feature labels Feb 21, 2025

VReaperV mentioned this pull request Feb 21, 2025

Implement Lottes HDR->LDR tonemapper #1550

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VReaperV linked an issue Feb 21, 2025 that may be closed by this pull request

adaptative lighting #29

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VReaperV force-pushed the adaptive-exposure branch 2 times, most recently from b1ef5f8 to b7277fe Compare February 23, 2025 13:05

VReaperV mentioned this pull request Feb 24, 2025

Some more material system clean-up #1563

Merged

VReaperV force-pushed the adaptive-exposure branch from b7277fe to 01ab8df Compare March 10, 2025 18:44

VReaperV force-pushed the adaptive-exposure branch from 01ab8df to d7b2a06 Compare March 11, 2025 05:58

VReaperV force-pushed the adaptive-exposure branch from d7b2a06 to 90becba Compare March 15, 2025 06:05

slipher reviewed Mar 15, 2025

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VReaperV force-pushed the adaptive-exposure branch 2 times, most recently from c5cb774 to fb62668 Compare March 16, 2025 19:38

VReaperV force-pushed the adaptive-exposure branch 2 times, most recently from 41564ef to f251a5e Compare March 16, 2025 20:07

VReaperV force-pushed the adaptive-exposure branch from f251a5e to d1f2c9c Compare March 17, 2025 23:28

slipher reviewed Mar 19, 2025

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VReaperV force-pushed the adaptive-exposure branch from 71adf84 to 8e25a56 Compare March 22, 2025 07:19

slipher reviewed Mar 26, 2025

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src/engine/renderer/glsl_source/cameraEffects_fp.glsl Outdated Show resolved Hide resolved

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VReaperV added 6 commits March 30, 2025 23:09

Implement adaptive exposure

9d5122f

Add a compute shader that will compute the geometric mean of scene luminance, then map it to an exposure curve in the `cameraEffects` shader. This is controlled by `r_tonemapAdaptiveExposure`.

Fix luminance overflow

5e05f12

Fix luminanceReduction shader name

78270c3

Shader ifdef checks for glConfig2.adaptiveExposureAvailable

d0a6ab7

Move GetAverageLuminance() to the correct ifdef

98fe168

Fix incorrect ifdef for subgroup atomics

86e7478

VReaperV force-pushed the adaptive-exposure branch from 682037b to 86e7478 Compare March 30, 2025 20:09

slipher reviewed Apr 2, 2025

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Implement adaptive exposure #1559

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Implement adaptive exposure #1559

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