From 7b6eec530c03e3e611d32269497416e728643897 Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Thu, 27 Feb 2025 18:36:15 +0100
Subject: [PATCH] render/vulkan: add luminance multipler for output shader

---
 include/render/vulkan.h           |  1 +
 render/vulkan/pass.c              | 12 ++++++++++++
 render/vulkan/shaders/output.frag |  3 +++
 3 files changed, 16 insertions(+)

diff --git a/include/render/vulkan.h b/include/render/vulkan.h
index 530fa1d27..b6bd0c2e8 100644
--- a/include/render/vulkan.h
+++ b/include/render/vulkan.h
@@ -339,6 +339,7 @@ struct wlr_vk_vert_pcr_data {
 
 struct wlr_vk_frag_output_pcr_data {
 	float matrix[4][4]; // only a 3x3 subset is used
+	float luminance_multiplier;
 	float lut_3d_offset;
 	float lut_3d_scale;
 };
diff --git a/render/vulkan/pass.c b/render/vulkan/pass.c
index 68ee78e67..ab044f6a0 100644
--- a/render/vulkan/pass.c
+++ b/render/vulkan/pass.c
@@ -149,6 +149,11 @@ static VkSemaphore render_pass_wait_sync_file(struct wlr_vk_render_pass *pass,
 	return *sem_ptr;
 }
 
+static float get_luminance_multiplier(const struct wlr_color_luminances *src_lum,
+		const struct wlr_color_luminances *dst_lum) {
+	return (dst_lum->reference / src_lum->reference) * (src_lum->max / dst_lum->max);
+}
+
 static bool render_pass_submit(struct wlr_render_pass *wlr_pass) {
 	struct wlr_vk_render_pass *pass = get_render_pass(wlr_pass);
 	struct wlr_vk_renderer *renderer = pass->renderer;
@@ -197,6 +202,7 @@ static bool render_pass_submit(struct wlr_render_pass *wlr_pass) {
 		}
 
 		struct wlr_vk_frag_output_pcr_data frag_pcr_data = {
+			.luminance_multiplier = 1,
 			.lut_3d_offset = 0.5f / dim,
 			.lut_3d_scale = (float)(dim - 1) / dim,
 		};
@@ -238,6 +244,12 @@ static bool render_pass_submit(struct wlr_render_pass *wlr_pass) {
 				pipeline = render_buffer->plain.render_setup->output_pipe_pq;
 				break;
 			}
+
+			struct wlr_color_luminances srgb_lum, dst_lum;
+			wlr_color_transfer_function_get_default_luminance(
+				WLR_COLOR_TRANSFER_FUNCTION_SRGB, &srgb_lum);
+			wlr_color_transfer_function_get_default_luminance(tf, &dst_lum);
+			frag_pcr_data.luminance_multiplier = get_luminance_multiplier(&srgb_lum, &dst_lum);
 		}
 		bind_pipeline(pass, pipeline);
 		vkCmdPushConstants(render_cb->vk, renderer->output_pipe_layout,
diff --git a/render/vulkan/shaders/output.frag b/render/vulkan/shaders/output.frag
index 7478e249d..f2d5d645c 100644
--- a/render/vulkan/shaders/output.frag
+++ b/render/vulkan/shaders/output.frag
@@ -10,6 +10,7 @@ layout(location = 0) out vec4 out_color;
 /* struct wlr_vk_frag_output_pcr_data */
 layout(push_constant, row_major) uniform UBO {
 	layout(offset = 80) mat4 matrix;
+	float luminance_multiplier;
 	float lut_3d_offset;
 	float lut_3d_scale;
 } data;
@@ -56,6 +57,8 @@ void main() {
 		rgb = in_color.rgb / alpha;
 	}
 
+	rgb *= data.luminance_multiplier;
+
 	rgb = mat3(data.matrix) * rgb;
 
 	if (OUTPUT_TRANSFORM == OUTPUT_TRANSFORM_LUT_3D) {