| 摘要 |
PROBLEM TO BE SOLVED: To enhance the use efficiency of a memory area by reducing the readout frequency to a frame buffer memory. SOLUTION: Minimum and maximum Z values are read from a Z limit buffer, and then, it is compared whether the Z value of a present pixel in an area is larger than the maximum Z value or not (S51, S52). When the Z value of the present pixel is larger, the present pixel is completely hidden, and then, the next Z value to be tested is obtained and it is judged that a pixel to be compared is additionally included in the area (S54, S58) or not. When the Z value of the present pixel is not larger, it is judged whether the Z value of the present pixel is smaller than the minimum Z value (S59) or not. When the Z value of the present pixel is smaller, the Z value of the present pixel is written into a Z buffer, while the minimum Z value is updated (S61). When the Z value of the present pixel is not smaller, a Z value of a pixel of the Z buffer is read and compared with the Z value of the present pixel (S62, S64). When the Z value of the present pixel is not less than the read Z value from the Z buffer, the present pixel is hidden and cancelled (S65). When the Z value of the present pixel is less than the read Z value, the Z value of the present pixel is written into the Z buffer, while the minimum Z value and the maximum Z value are updated (S66).
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