beginRenderMask method
Implementation
@override
void beginRenderMask(RenderState renderState, RenderMask mask) {
final matrix = renderState.globalMatrix;
_renderingContext.setTransform(
matrix.a, matrix.b, matrix.c, matrix.d, matrix.tx, matrix.ty);
_renderingContext.beginPath();
mask.renderMask(renderState);
_renderingContext.save();
_renderingContext.clip();
}