shader method
Implementation
VisualEffect shader(
String assetKey,
double devicePixelRatio,
ShaderBuilder onGenerateShader,
) {
return _ShaderVisualEffect(
assetKey: assetKey,
onGenerateShader: onGenerateShader,
devicePixelRatio: devicePixelRatio,
childSize: childSize,
childEffect: this,
);
}