add cell-span grid with resize handles, 3d water surface effect, and shader preset system with double-click popup menu

shaders/vial_fill.gdshader

@@ -128,15 +128,31 @@ void fragment() {
 	// tiny sparkle
 	effect_rgb += 0.03 * vec3(sin(t * 3.0), cos(t * 2.0), noise_val * 0.1);
 
+	// --- 3D water surface ---
+	float d_surf = UV.y - fill_line;  // positive = below surface
+	float d_abs = abs(d_surf);
+
+	// subsurface light scatter — brightest just below surface, fades with depth
+	float subsurface = exp(-d_surf * 25.0) * step(0.0, d_surf);
+	effect_rgb *= 1.0 + subsurface * 0.25;
+
 	// --- composite ---
 	vec3 col = bg_color.rgb;
 	col = mix(col, effect_rgb, liquid);
 
-	// surface foam line (wider glow + bright core)
-	float foam_glow = smoothstep(fill_line - 0.02, fill_line, UV.y) - smoothstep(fill_line, fill_line + 0.004, UV.y);
-	col += foam_glow * vec3(0.5, 0.65, 0.9) * 0.6 * liquid;
-	float foam_core = smoothstep(fill_line - 0.006, fill_line, UV.y) - smoothstep(fill_line, fill_line + 0.001, UV.y);
-	col += foam_core * vec3(0.7, 0.85, 1.0) * liquid;
+	// foam glow — smooth double-sided falloff (gaussian-like)
+	float foam_glow = exp(-d_abs * 70.0);
+	float foam_core = exp(-d_abs * 350.0);
+	vec3 foam_tint = vec3(0.6, 0.75, 0.95);
+	col += foam_glow * foam_tint * 0.5;
+	col += foam_core * vec3(0.75, 0.9, 1.0) * 0.6;
+
+	// wave-slope highlight — brightens at wave crests facing the viewer
+	float wave_slope = (cos(UV.x * wf + TIME * 5.0) * wf
+		+ cos(UV.x * wf * 1.7 + TIME * 7.0 + 1.3) * wf * 1.7 * 0.5
+		+ cos(UV.x * wf * 0.6 + TIME * 2.5 + 2.9) * wf * 0.6 * 0.3) * edge_damp / 1.8 * wave_amp;
+	float slope_highlight = max(0.0, wave_slope) * exp(-d_abs * 200.0);
+	col += slope_highlight * vec3(0.6, 0.8, 1.0) * 0.4;
 
 	// border
 	col = mix(col, border_color.rgb, outer - inner);