A disclosed method for displaying a shape of an object including a trimmed surface generated based on a base surface includes: dividing the base surface into plural triangles; generating a loop polygon for loops including an outer loop for defining an outer shape of the trimmed surface and an inner loop provided, in the outer loop, depending on the shape of the object; identifying plural sight-line single-valued areas, each of which satisfies a condition that mapping onto a projection surface is bijection, includes plural triangles, and is an area on the base surface, based on a positional relationship between a viewpoint and the base surface; generating, for each of the plural sight-line single-valued areas, mask data for each pixel from the sight-line single-valued area and the loop polygon; generating image data on the projection surface for each of the triangles; and perform drawing using the mask data and image data.