fix: Address incorrect opacity values when displaying RGB images in ImageMapper

Author: swederik

Sources/Rendering/OpenGL/ImageMapper/index.js

@@ -303,7 +303,7 @@ function vtkOpenGLImageMapper(publicAPI, model) {
               'vec4 tcolor = cscale0*texture2D(texture1, tcoordVCVSOutput.st) + cshift0;',
               'gl_FragData[0] = vec4(texture2D(colorTexture1, vec2(tcolor.r,0.5)).r,',
               '  texture2D(colorTexture1, vec2(tcolor.g,0.5)).r,',
-              '  texture2D(colorTexture1, vec2(tcolor.b,0.5)).r, tcolor.a);',
+              '  texture2D(colorTexture1, vec2(tcolor.b,0.5)).r, opacity);',
             ]
           ).result;
       }