Fix alpha output (no gamma nor linear correction)

src/Materials/Node/Blocks/Dual/textureBlock.ts

@@ -332,13 +332,15 @@ export class TextureBlock extends NodeMaterialBlock {
 
         state.compilationString += `${this._declareOutput(output, state)} = ${this._tempTextureRead}.${swizzle}${complement};\r\n`;
 
-        state.compilationString += `#ifdef ${this._linearDefineName}\r\n`;
-        state.compilationString += `${output.associatedVariableName} = toGammaSpace(${output.associatedVariableName});\r\n`;
-        state.compilationString += `#endif\r\n`;
-
-        state.compilationString += `#ifdef ${this._gammaDefineName}\r\n`;
-        state.compilationString += `${output.associatedVariableName} = toLinearSpace(${output.associatedVariableName});\r\n`;
-        state.compilationString += `#endif\r\n`;
+        if (swizzle !== 'a') { // no conversion if the output is "a" (alpha)
+            state.compilationString += `#ifdef ${this._linearDefineName}\r\n`;
+            state.compilationString += `${output.associatedVariableName} = toGammaSpace(${output.associatedVariableName});\r\n`;
+            state.compilationString += `#endif\r\n`;
+
+            state.compilationString += `#ifdef ${this._gammaDefineName}\r\n`;
+            state.compilationString += `${output.associatedVariableName} = toLinearSpace(${output.associatedVariableName});\r\n`;
+            state.compilationString += `#endif\r\n`;
+        }
     }
 
     protected _buildBlock(state: NodeMaterialBuildState) {