Fullneb Revamp (scp-fs2open#7352)

* change to new fog system

* Fix fog conversion issues

* remove unused old neb values

* Update scripting API

* temporary old-value round trip

* Rewrite nebula fog with four explicit parameters

Replace the legacy `+Fog Near Mult` / `+Fog Far Mult` model — which
depended on fixed engine constants — with four parameters that map
directly to renderer behavior:

  +Fog 1000m Visibility    fraction of light surviving 1000m of fog
  +Fog Near Distance       meters from camera where fog begins
  +Fog Skybox Clip Distance  max render distance for the skybox in fog
  +Fog Clip Distance       max render distance for the scene in fog

The deferred-lighting fog shader, material system, model renderer,
object sort, and the Lua mission API all consume the new parameters
directly. The legacy `Neb2_fog_near_mult` / `Neb2_fog_far_mult`
globals are removed.

Mission parsing accepts either the legacy keys or the modern keys.
Legacy values are converted to the modern set at parse time, and a
per-mission flag (`Neb2_fog_use_legacy_values`) records which keys to
write back on save. The flag is cleared only when something actually
changes, so opening and OK'ing an unmodified legacy mission preserves
its on-disk format. Saving uses `optional_string_fred` to preserve
user comments through edit cycles.

FRED2 and QtFRED background editors both expose the four parameters
in place of the old multipliers, with friendly labels and tooltips.
Both editors validate input (visibility clamped to [0, 1]; near
distance must be > 0; skybox and scene clip distances may be 0 to
disable fog at that range) and use a snapshot-and-compare at close
time so that a no-op open-then-OK never spuriously rewrites a legacy
mission in the modern format.

FRED2's background dialog is also reorganized so that "Display bg
bitmaps in nebula", "Override nebula fog palette", the RGB row, and
the four fog parameters all sit inside the Nebula group box; the
"Old Nebula" group box is restored below it with its Pattern, Color,
Pitch, Bank, and Heading controls back inside the frame. The dialog
now overrides PreTranslateMessage so that the new fog tooltips —
and the previously broken "Save sun/bitmap angles in correct format"
tooltip — actually fire.

QtFRED's BackgroundEditor.ui adds four QDoubleSpinBox controls in
the existing nebula form layout, with per-field decimals chosen to
avoid scientific notation, and per-field min/max declaring the
validation rules. The QtFRED help page is updated to describe the
new fields.

* fix tooltips

* restore forward-renderer fog

* Clang Tidy

* address feedback

* Refine nebula fog rewrite

- Rename Neb2_fog_use_legacy_values to Neb2_fog_save_legacy_values
  to reflect that the flag governs save format, not runtime
  behavior.
- Decide both the save flag and the legacy-to-modern conversion
  purely from whether the file contains modern fog keys, dropping
  the prior heuristic based on required_fso_version. A mission
  without modern keys (legacy- or retail-format) converts on load
  and saves back in legacy format; missions with modern keys are
  saved as modern.
- Snapshot the four fog values as floats at editor open and use
  fl_equal for the no-change comparison in both FRED2 and QtFRED,
  replacing the FRED2 CString comparison and the QtFRED strict
  inequality.
- Document the on-disk invariant in missionsave: when not saving
  legacy keys, the four modern keys must always be written (never
  gated on "only if non-default"), since the parser uses their
  presence to decide whether to run the conversion on next load.

---------

Co-authored-by: Goober5000 <ipw47@mailbox.org>

Author: BMagnu

code/def_files/data/effects/fog-f.sdr

@@ -15,6 +15,9 @@ layout (std140) uniform genericData {
 	float fog_density;
 	float zNear;
 	float zFar;
+
+	float clip_inf_dist;
+	float clip_dist;
 };
 
 void main()
@@ -28,6 +31,9 @@ void main()
 	// Now we compute the depth value in projection space using the clipping plane information
 	float view_depth = 2.0 * zNear * zFar / (zFar + zNear - depth_normalized * (zFar - zNear));
 
+	float skybox_compat_fake = step(1.0, depth_val);
+	view_depth = clamp(view_depth, 0.0, mix(clip_dist, clip_inf_dist, skybox_compat_fake));
+
 	if (isinf(view_depth)) {
 		fragOut0.rgb = color_in.rgb;
 	} else {

code/def_files/data/effects/main-f.sdr

@@ -39,8 +39,8 @@ layout (std140) uniform modelData {
 	model_light lights[MAX_LIGHTS];
 
 	float outlineWidth;
-	float fogStart;
-	float fogScale;
+	float fogNear;
+	float fogDensity;
 	int buffer_matrix_offset;
 
 	vec4 clip_equation;
@@ -376,9 +376,10 @@ void main()
 		#prereplace ENDIF_FLAG //MODEL_SDR_FLAG_DIFFUSE
 		// This code will only be used by the forward renderer so we apply the fog effect to both the emissive and the base
 		// color.
-		baseColor.rgb = mix(emissiveColor.rgb + baseColor.rgb, finalFogColor, vertIn.fogDist);
+		float fogDensityFinal = clamp(1 - pow(fogDensity, vertIn.fogDist) , 0.0, 1.0);
+		baseColor.rgb = mix(emissiveColor.rgb + baseColor.rgb, finalFogColor, fogDensityFinal);
 		emissiveColor.rgb = vec3(0.0); // Zero the emissive color since it has already been added by the previous line
-		specColor.rgb *= vertIn.fogDist;
+		specColor.rgb *= fogDensityFinal;
 	#prereplace ENDIF_FLAG //MODEL_SDR_FLAG_FOG
 
 	#prereplace IF_FLAG MODEL_SDR_FLAG_DIFFUSE

code/def_files/data/effects/main-g.sdr

@@ -45,8 +45,8 @@ layout (std140) uniform modelData {
 	model_light lights[MAX_LIGHTS];
 
 	float outlineWidth;
-	float fogStart;
-	float fogScale;
+	float fogNear;
+	float fogDensity;
 	int buffer_matrix_offset;
 
 	vec4 clip_equation;

code/def_files/data/effects/main-v.sdr

@@ -40,8 +40,8 @@ layout (std140) uniform modelData {
 	model_light lights[MAX_LIGHTS];
 
 	float outlineWidth;
-	float fogStart;
-	float fogScale;
+	float fogNear;
+	float fogDensity;
 	int buffer_matrix_offset;
 
 	vec4 clip_equation;
@@ -189,7 +189,7 @@ void main()
 	vertOut.tangentMatrix = mat3(t, b, normal);
 
 	#prereplace IF_FLAG MODEL_SDR_FLAG_FOG
-		vertOut.fogDist = clamp((gl_Position.z - fogStart) * 0.75 * fogScale, 0.0, 1.0);
+		vertOut.fogDist = gl_Position.z - fogNear;
 	#prereplace ENDIF_FLAG //MODEL_SDR_FLAG_FOG
 
 	#prereplace IF_FLAG MODEL_SDR_FLAG_TRANSFORM

code/graphics/material.cpp

@@ -674,14 +674,12 @@ bool model_material::is_batched() const
 	return Batched;
 }
 
-void model_material::set_fog(int r, int g, int b, float _near, float _far)
+void model_material::set_fog(int r, int g, int b)
 {
 	Fog_params.enabled = true;
 	Fog_params.r = r;
 	Fog_params.g = g;
 	Fog_params.b = b;
-	Fog_params.dist_near = _near;
-	Fog_params.dist_far = _far;
 }
 
 void model_material::set_fog()

code/graphics/material.h

@@ -172,8 +172,6 @@ class model_material : public material
 		int r = 0;
 		int g = 0;
 		int b = 0;
-		float dist_near = -1.0f;
-		float dist_far = -1.0f;
 	};
 
  private:
@@ -255,7 +253,7 @@ class model_material : public material
     int get_shader_runtime_early_flags() const;
 	int get_shader_runtime_flags() const;
 
-	void set_fog(int r, int g, int b, float near, float far);
+	void set_fog(int r, int g, int b);
 	void set_fog();
 	bool is_fogged() const;
 	const fog& get_fog() const;

code/graphics/opengl/gropengldeferred.cpp

@@ -542,8 +542,8 @@ void gr_opengl_deferred_lighting_finish()
 		GL_state.Texture.Enable(0, GL_TEXTURE_2D, Scene_composite_texture);
 		GL_state.Texture.Enable(1, GL_TEXTURE_2D, Scene_depth_texture);
 
-		float fog_near, fog_far, fog_density;
-		neb2_get_adjusted_fog_values(&fog_near, &fog_far, &fog_density);
+		float fog_near, fog_density;
+		neb2_get_adjusted_fog_values(&fog_near, &fog_density);
 		unsigned char r, g, b;
 		neb2_get_fog_color(&r, &g, &b);
 
@@ -558,6 +558,8 @@ void gr_opengl_deferred_lighting_finish()
 			data->fog_color.xyz.z = b / 255.f;
 			data->zNear           = Min_draw_distance;
 			data->zFar            = Max_draw_distance;
+			data->clip_inf_dist	  = Neb2_fog_skybox_clip_distance;
+			data->clip_dist       = Neb2_fog_clip_distance;
 		});
 
 		opengl_draw_full_screen_textured(0.0f, 0.0f, 1.0f, 1.0f);

code/graphics/uniforms.cpp

@@ -6,6 +6,7 @@
 #include "light.h"
 #include "globalincs/systemvars.h"
 #include "shadows.h"
+#include "nebula/neb.h"
 
 #define MODEL_SDR_FLAG_MODE_CPP
 #include "def_files/data/effects/model_shader_flags.h"
@@ -218,8 +219,11 @@ void convert_model_material(model_uniform_data* data_out,
 		auto& fog_params = material.get_fog();
 
 		if (fog_params.enabled) {
-			data_out->fogStart = fog_params.dist_near;
-			data_out->fogScale = 1.0f / (fog_params.dist_far - fog_params.dist_near);
+			float fog_near, fog_density;
+			neb2_get_adjusted_fog_values(&fog_near, &fog_density);
+			data_out->fogNear = fog_near;
+			data_out->fogDensity = fog_density;
+
 			data_out->fogColor.xyzw.x = i2fl(fog_params.r) / 255.0f;
 			data_out->fogColor.xyzw.y = i2fl(fog_params.g) / 255.0f;
 			data_out->fogColor.xyzw.z = i2fl(fog_params.b) / 255.0f;

code/graphics/util/uniform_structs.h

@@ -87,8 +87,8 @@ struct model_uniform_data {
 	model_light lights[MAX_UNIFORM_LIGHTS];
 
 	float outlineWidth;
-	float fogStart;
-	float fogScale;
+	float fogNear;
+	float fogDensity;
 	int buffer_matrix_offset;
 
 	vec4 clip_equation;
@@ -288,8 +288,10 @@ struct fog_data {
 	float fog_density;
 	float zNear;
 	float zFar;
+	float clip_inf_dist;
+	float clip_dist;
 
-	float pad[1];
+	float pad[3];
 };
 
 struct volumetric_fog_data {

code/mission/missionparse.cpp

@@ -857,11 +857,45 @@ void parse_mission_info(mission *pm, bool basic = false)
 		if (!basic)
 			nebl_set_storm(Mission_parse_storm_name);
 	}
-	if(optional_string("+Fog Near Mult:")){
-		stuff_float(&Neb2_fog_near_mult);
+
+	bool found_neb2_modern = false;
+
+	if (optional_string("+Fog Near Mult:")) {
+		stuff_float(&Neb2_fog_legacy_near_mult);
+	}
+	if (optional_string("+Fog Far Mult:")) {
+		stuff_float(&Neb2_fog_legacy_far_mult);
+	}
+
+	// Look for the modern values
+	if (optional_string("+Fog 1000m Visibility:")) {
+		stuff_float(&Neb2_fog_1000m_visibility);
+		found_neb2_modern = true;
+	}
+	if (optional_string("+Fog Near Distance:")) {
+		stuff_float(&Neb2_fog_near_distance);
+		found_neb2_modern = true;
 	}
-	if(optional_string("+Fog Far Mult:")){
-		stuff_float(&Neb2_fog_far_mult);
+	if (optional_string("+Fog Skybox Clip Distance:")) {
+		stuff_float(&Neb2_fog_skybox_clip_distance);
+		found_neb2_modern = true;
+	}
+	if (optional_string("+Fog Clip Distance:")) {
+		stuff_float(&Neb2_fog_clip_distance);
+		found_neb2_modern = true;
+	}
+
+	// write legacy values on save if we are compatible with older formats
+	Neb2_fog_save_legacy_values = !found_neb2_modern;
+
+	// Convert legacy values if this mission was made before modern values were introduced
+	if (!found_neb2_modern) {
+		//This stems from the weird unchangeable constants of legacy fog
+		float denom = std::max(75.f * Neb2_fog_legacy_far_mult - Neb2_fog_legacy_near_mult, 1.0f);
+		Neb2_fog_1000m_visibility = powf(10.f, -100.f / denom);
+		Neb2_fog_near_distance = 10.f * Neb2_fog_legacy_near_mult;
+		Neb2_fog_skybox_clip_distance = 0.f; // Apparently, skybox fog was just outright broken...
+		Neb2_fog_clip_distance = Default_max_draw_distance;
 	}
 
 	// Goober5000 - ship contrail speed threshold
@@ -9614,6 +9648,9 @@ bool check_for_25_1_data()
 	if (count_items_with_value(Props) > 0)
 		return true;
 
+	if (The_mission.flags[Mission::Mission_Flags::Fullneb] && !Neb2_fog_save_legacy_values)
+		return true;
+
 	constexpr auto defaultLayer = "Default";
 
 	for (const auto& so : list_range(&Ship_obj_list))