Fix #795

Author: hzqst

Build/svencoop/renderer/shader/studio_shader.frag.glsl

@@ -548,6 +548,18 @@ vec3 R_StudioCelShade(vec3 v_color, vec3 normalWS, vec3 lightdirWS, float specul
     // N dot L
     float litOrShadowArea = smoothstep(r_celshade_midpoint - r_celshade_softness, r_celshade_midpoint + r_celshade_softness, NoL);
 
+#if defined(STUDIO_NF_CELSHADE_FACE)
+	// When the light direction is nearly vertical, the Z-flattening in
+	// R_GetAdjustedLightDirection has no horizontal component to preserve,
+	// so normalize() pushes L back to vertical, causing a "vertical shadow"
+	// artifact on the face. Fade toward no shadow to suppress it.
+	{
+		float flLightHorizLen = length(lightdirWS.xy);
+		float flVerticalFade = smoothstep(0.05, 0.2, flLightHorizLen);
+		litOrShadowArea = mix(1.0, litOrShadowArea, flVerticalFade);
+	}
+#endif
+
 #if defined(STUDIO_NF_CELSHADE_FACE) && defined(STENCIL_TEXTURE_ENABLED)
 
 	litOrShadowArea = mix(0.5, 1.0, litOrShadowArea);