vk: add `surfhash` argument to `rt_debug_display_only`

Allows highlighting all the surfaces with random colors to easily see
the surfaces structure and boundaries.

Fixes #635

ref/vk/TODO.md

@@ -1,6 +1,7 @@
 # 2023-11-03 E324
 - [x] add cvar for displaying only specified channel
-- [ ] r_lightmap
+- [x] r_lightmap
+- [x] hightlight all surfaces with random colors
 - [ ] massage shaders: consolidate all bindings explicitly
 - [ ] skip sorting-by-texture when loading brush models ~~(=> geometry count explosion; i.e. kusochki count will explode too)~~
 - [ ] kusochki-vs-materials structures

ref/vk/shaders/ray_interop.h

@@ -175,6 +175,7 @@ struct PushConstants {
 #define DEBUG_DISPLAY_NSHADE 4
 #define DEBUG_DISPLAY_NGEOM 5
 #define DEBUG_DISPLAY_LIGHTING 6
+#define DEBUG_DISPLAY_SURFHASH 7
 // add more when needed
 
 struct UniformBuffer {

ref/vk/shaders/ray_primary_hit.glsl

@@ -8,6 +8,8 @@
 #include "rt_geometry.glsl"
 #include "color_spaces.glsl"
 
+#include "noise.glsl" // for DEBUG_DISPLAY_SURFHASH
+
 layout(set = 0, binding = 6) uniform sampler2D textures[MAX_TEXTURES];
 layout(set = 0, binding = 2) uniform UBO { UniformBuffer ubo; } ubo;
 layout(set = 0, binding = 7) uniform samplerCube skybox;
@@ -103,6 +105,11 @@ void primaryRayHit(rayQueryEXT rq, inout RayPayloadPrimary payload) {
 
 	payload.base_color_a *= color;
 	payload.emissive.rgb *= color.rgb;
+
+	if (ubo.ubo.debug_display_only == DEBUG_DISPLAY_SURFHASH) {
+		const uint hash = xxhash32(geom.kusok_index);
+		payload.emissive.rgb = vec3(0xff & (hash>>16), 0xff & (hash>>8), 0xff & hash) / 255.;
+	}
 }
 
 #endif // ifndef RAY_PRIMARY_HIT_GLSL_INCLUDED

ref/vk/vk_rtx.c

@@ -163,6 +163,7 @@ static void parseDebugDisplayValue( void ) {
 	X(EMISSIVE) \
 	X(NSHADE) \
 	X(NGEOM) \
+	X(SURFHASH) \
 
 #define X(suffix) \
 	if (0 == Q_stricmp(cvalue, #suffix)) { \