A computer-implemented display processing method for displaying a shape of an object including a trimmed surface generated based on a base surface, the display processing method comprising: dividing the base surface into a plurality of 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 (S5, S7) one or 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 which is behind the projection surface when viewed from the viewpoint; generating, for each of the one or plural sight-line single-valued areas, mask data from the sight-line single-valued area and the loop polygon, wherein the mask data is data for controlling whether or not display is performed for each pixel; generating image data on the projection surface for each of the plurality of triangles; and performing a drawing processing from the mask data and the image data, wherein the generating of the mask data comprises: generating outer loop intersection that is intersection between an outer loop polygon, which is a loop polygon for an outer loop among the loop polygons stored in the data storage unit, and the sight-line single-valued area; generating inner loop intersection that is intersection between an inner loop polygon, which is a loop polygon for an inner loop among the loop polygons, and the sight-line single-valued area; setting mask data of first pixels on the projection surface, which correspond to points within the outer loop intersection so as to represent the first pixels are to be displayed; and setting mask data of second pixels on the projection surface, which correspond to points within the inner loop intersection so as to represent the second pixels are not to be displayed. dividing the base surface into a plurality of 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 (S5, S7) one or 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 which is behind the projection surface when viewed from the viewpoint; generating, for each of the one or plural sight-line single-valued areas, mask data from the sight-line single-valued area and the loop polygon, wherein the mask data is data for controlling whether or not display is performed for each pixel; generating image data on the projection surface for each of the plurality of triangles; and performing a drawing processing from the mask data and the image data, wherein the generating of the mask data comprises: generating outer loop intersection that is intersection between an outer loop polygon, which is a loop polygon for an outer loop among the loop polygons stored in the data storage unit, and the sight-line single-valued area; generating inner loop intersection that is intersection between an inner loop polygon, which is a loop polygon for an inner loop among the loop polygons, and the sight-line single-valued area; setting mask data of first pixels on the projection surface, which correspond to points within the outer loop intersection so as to represent the first pixels are to be displayed; and setting mask data of second pixels on the projection surface, which correspond to points within the inner loop intersection so as to represent the second pixels are not to be displayed. generating outer loop intersection that is intersection between an outer loop polygon, which is a loop polygon for an outer loop among the loop polygons stored in the data storage unit, and the sight-line single-valued area; generating inner loop intersection that is intersection between an inner loop polygon, which is a loop polygon for an inner loop among the loop polygons, and the sight-line single-valued area; setting mask data of first pixels on the projection surface, which correspond to points within the outer loop intersection so as to represent the first pixels are to be displayed; and setting mask data of second pixels on the projection surface, which correspond to points within the inner loop intersection so as to represent the second pixels are not to be displayed.