From 22a7fd1cf3b9cd6b2c306e234f22885b9ddcc40f Mon Sep 17 00:00:00 2001
From: jpark37 <jpark37@users.noreply.github.com>
Date: Tue, 19 Jan 2021 11:17:50 -0800
Subject: [PATCH] obs-filters: Apply color grade filter in linear space

---
 plugins/obs-filters/color-grade-filter.c      |  2 ++
 .../data/color_grade_filter.effect            | 28 ++++++++++++++++---
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/plugins/obs-filters/color-grade-filter.c b/plugins/obs-filters/color-grade-filter.c
index 8d814e69b..d7849063d 100644
--- a/plugins/obs-filters/color-grade-filter.c
+++ b/plugins/obs-filters/color-grade-filter.c
@@ -452,8 +452,10 @@ static void color_grade_filter_render(void *data, gs_effect_t *effect)
 	param = gs_effect_get_param_by_name(filter->effect, "cube_width_i");
 	gs_effect_set_float(param, 1.0f / filter->cube_width);
 
+	const bool previous = gs_set_linear_srgb(true);
 	obs_source_process_filter_tech_end(filter->context, filter->effect, 0,
 					   0, tech_name);
+	gs_set_linear_srgb(previous);
 
 	UNUSED_PARAMETER(effect);
 }
diff --git a/plugins/obs-filters/data/color_grade_filter.effect b/plugins/obs-filters/data/color_grade_filter.effect
index 426009de1..ba05bc409 100644
--- a/plugins/obs-filters/data/color_grade_filter.effect
+++ b/plugins/obs-filters/data/color_grade_filter.effect
@@ -35,9 +35,29 @@ VertDataOut VSDefault(VertDataIn v_in)
 	return vert_out;
 }
 
+float srgb_linear_to_nonlinear_channel(float u)
+{
+	return (u <= 0.0031308) ? (12.92 * u) : ((1.055 * pow(u, 1.0 / 2.4)) - 0.055);
+}
+
+float4 srgb_linear_to_nonlinear(float4 v)
+{
+	return float4(srgb_linear_to_nonlinear_channel(v.r), srgb_linear_to_nonlinear_channel(v.g), srgb_linear_to_nonlinear_channel(v.b), v.a);
+}
+
+float srgb_nonlinear_to_linear_channel(float u)
+{
+	return (u <= 0.04045) ? (u / 12.92) : pow((u + 0.055) / 1.055, 2.4);
+}
+
+float4 srgb_nonlinear_to_linear(float4 v)
+{
+	return float4(srgb_nonlinear_to_linear_channel(v.r), srgb_nonlinear_to_linear_channel(v.g), srgb_nonlinear_to_linear_channel(v.b), v.a);
+}
+
 float4 LUT1D(VertDataOut v_in) : TARGET
 {
-	float4 textureColor = image.Sample(textureSampler, v_in.uv);
+	float4 textureColor = srgb_linear_to_nonlinear(image.Sample(textureSampler, v_in.uv));
 
 	if (textureColor.r >= domain_min.r && textureColor.r <= domain_max.r) {
 		float u = textureColor.r * clut_scale.r + clut_offset.r;
@@ -57,12 +77,12 @@ float4 LUT1D(VertDataOut v_in) : TARGET
 		textureColor.b = lerp(textureColor.b, channel, clut_amount);
 	}
 
-	return textureColor;
+	return srgb_nonlinear_to_linear(textureColor);
 }
 
 float4 LUT3D(VertDataOut v_in) : TARGET
 {
-	float4 textureColor = image.Sample(textureSampler, v_in.uv);
+	float4 textureColor = srgb_linear_to_nonlinear(image.Sample(textureSampler, v_in.uv));
 	float r = textureColor.r;
 	float g = textureColor.g;
 	float b = textureColor.b;
@@ -145,7 +165,7 @@ float4 LUT3D(VertDataOut v_in) : TARGET
 		textureColor.rgb = lerp(textureColor.rgb, luttedColor, clut_amount);
 	}
 
-	return textureColor;
+	return srgb_nonlinear_to_linear(textureColor);
 }
 
 technique Draw1D