A method of operating a graphic processor performing sampling-based rendering involves intermediate rendering by shading-processing some fragments of a first frame by using a first sample candidate map having a first pattern. Further intermediate rendering may also be performed by shading-processing some fragments of a second frame by using a first sample candidate map having a second pattern. Other fragments of the second frame may be additionally sampled, where these other fragments may be determined based on comparing a shading processing result of the first frame and a shading processing result of the second frame. Final rendering may be performed by shading-processing the additionally sampled fragments.