NodeMaterial: Fix alpha discard. (#31927)

src/materials/nodes/NodeMaterial.js

@@ -12,7 +12,7 @@ import { materialReference } from '../../nodes/accessors/MaterialReferenceNode.j
 import { positionLocal, positionView } from '../../nodes/accessors/Position.js';
 import { skinning } from '../../nodes/accessors/SkinningNode.js';
 import { morphReference } from '../../nodes/accessors/MorphNode.js';
-import { mix } from '../../nodes/math/MathNode.js';
+import { fwidth, mix, smoothstep } from '../../nodes/math/MathNode.js';
 import { float, vec3, vec4, bool } from '../../nodes/tsl/TSLBase.js';
 import AONode from '../../nodes/lighting/AONode.js';
 import { lightingContext } from '../../nodes/lighting/LightingContextNode.js';
@@ -843,7 +843,16 @@ class NodeMaterial extends Material {
 
 			alphaTestNode = this.alphaTestNode !== null ? float( this.alphaTestNode ) : materialAlphaTest;
 
-			diffuseColor.a.lessThanEqual( alphaTestNode ).discard();
+			if ( this.alphaToCoverage === true ) {
+
+				diffuseColor.a = smoothstep( alphaTestNode, alphaTestNode.add( fwidth( diffuseColor.a ) ), diffuseColor.a );
+				diffuseColor.a.lessThanEqual( 0 ).discard();
+
+			} else {
+
+				diffuseColor.a.lessThanEqual( alphaTestNode ).discard();
+
+			}
 
 		}
 
@@ -863,10 +872,6 @@ class NodeMaterial extends Material {
 
 			diffuseColor.a.assign( 1.0 );
 
-		} else if ( alphaTestNode === null ) {
-
-			diffuseColor.a.lessThanEqual( 0 ).discard();
-
 		}
 
 	}