1. A computer graphics rendering apparatus for generating a screen image, using plural texture images having different mipmap levels, the apparatus comprising: a first coordinate generating unit configured to generate a normalized texture coordinate of a texture image; a second coordinate generating unit configured to generate, from the normalized texture coordinate of the texture image, a texel coordinate of a texel in the texture image, according to a mipmap level of the texture image; and an index generating unit configured to generate, regarding an image block in the texture image, an index value indicating a cache line corresponding to the image block, using a texel coordinate of a texel in the image block, the index generating unit generating the index value such that index values of image blocks in the same position are different, between two texture images having mipmap levels adjacent to each other.