vk: rt: linearize kusochki.color/override_color

ref/vk/NOTES.md

@@ -1087,3 +1087,32 @@ Original:
 Our:
     `color = sqrt(a*a + b*b)`
 There's nothing we can to do `a` only that would make it fake the "original" mixing result.
+
+# 2023-12-28 E353
+## Passing colors from all over the place into `trace_simple_blending.glsl`
+- color = mm_color * texture_color * geom.vertex_color * alpha
+	- alpha = mm_color.a * texture_color.a * geom.vertex_color.a
+	- mm_color = model.color * kusok.material.base_color
+		- model.color -- already linearized
+		- kusok.material.base_color = mat->base_color * override_color
+			- mat->base_color -- specified in .mat files by hand
+				- [x] Which colorspace should it be specified in?
+				      Currently it is passed in as is, which means that it's accidentally linear.
+			- override_color -- passed from the engine through `R_RenderDrawOnce()`, called from triapi
+				- [x] sRGB-γ, should linearize
+	- texture_color -- just texture sampled color. sRGB-γ vs linear is specified at VkImageView level at loading time
+	- geom.vertex_color -- barycentric-lerped from vk_vertex[].color
+		- vk_vertex[].color -- rgba8
+			- [x] which colorspace? Should be sRGB-γ originally
+		- [x] Do we need to linearize it? YES
+			- [x] Before lerping or after? BEFORE -- already done
+
+- Should α be converted from gamma to linear?
+	- Doing so:
+		- seems kinda logical -- everything is gamma-space in engine, so it probably should be.
+		- fixes some 'background' sprites transparency
+		- makes too-brighs c0a0c beams darker (but kinda too dark imo)
+		- breaks sprite animation lerping -- now we need 2 native gamma-to-linear functions, wich alpha conv and w/o
+
+As usual -- original sRGB-specialized game art is painfully incompatible with modern linear PBR.
+The best way to address it (hopefully w/o breaking too much linear rendering math) remains to be discovered.

ref/vk/TODO.md

@@ -1,3 +1,7 @@
+# 2023-12-28 E353
+- [x] track color spaces when passing colors into shaders
+- [ ] validation failure at startup, #723
+
 Longer-term agenda for current season:
 - [ ] Better PBR math, e.g.:
 	- [ ] Black metals: https://github.com/w23/xash3d-fwgs/issues/666

ref/vk/vk_ray_model.c

@@ -337,6 +337,15 @@ static void sRGBtoLinearVec4(const vec4_t in, vec4_t out) {
 	out[3] = in[3];
 }
 
+static void sRGBAtoLinearVec4(const vec4_t in, vec4_t out) {
+	out[0] = sRGBtoLinearScalar(in[0]);
+	out[1] = sRGBtoLinearScalar(in[1]);
+	out[2] = sRGBtoLinearScalar(in[2]);
+
+	// α also needs to be linearized.
+	out[3] = sRGBtoLinearScalar(in[3]);
+}
+
 void RT_FrameAddModel( struct rt_model_s *model, rt_frame_add_model_t args ) {
 	if (!model || !model->blas)
 		return;
@@ -476,7 +485,7 @@ void RT_FrameAddOnce( rt_frame_add_once_t args ) {
 			break;
 		}
 
-		Vector4Copy(*args.color, dyn->colors[dyn->geometries_count]);
+		sRGBAtoLinearVec4(*args.color_srgb, dyn->colors[dyn->geometries_count]);
 		dyn->geometries[dyn->geometries_count++] = args.geometries[i];
 	}
 }

ref/vk/vk_render.c

@@ -844,7 +844,7 @@ void R_RenderDrawOnce(r_draw_once_t args) {
 		RT_FrameAddOnce((rt_frame_add_once_t){
 			.debug_name = args.name,
 			.geometries = &geometry,
-			.color = args.color,
+			.color_srgb = args.color,
 			.geometries_count = 1,
 			.render_type = args.render_type,
 		});

ref/vk/vk_rtx.h

@@ -78,7 +78,7 @@ void RT_FrameAddModel( struct rt_model_s *model, rt_frame_add_model_t args );
 typedef struct {
 	const char *debug_name;
 	const struct vk_render_geometry_s *geometries;
-	const vec4_t *color;
+	const vec4_t *color_srgb;
 	int geometries_count;
 	int render_type;
 } rt_frame_add_once_t;