■ Pre-clipping disabled
∙ One drawing command is formed by a set of several lines, and each line is a set of several dots. Each dot is drawn based on the clipping area (drawing area) information specified by the CPU.
∙ Lines that are completely out of the drawing area and do not require drawing of the entire line can be detected in advance, and drawing efficiency will be improved if drawing is not started. Also, if one end point of one line is outside the drawing area, it is more efficient to start drawing from within the drawing area (the line is limited to the horizontal or vertical direction).
VDP1 normally performs the detection work, but when drawing a small size in the direction of vertex (A)-(B) or (D)-(C), the overhead due to the detection work (up to 5 CPU clocks per line) ) Is conspicuous and causes the drawing efficiency to decrease.
¡If the size is large and it protrudes greatly from the drawing area, pre-clipping will be more efficient.
This bit is valid only for drawing commands. Fix to 0 for other commands.
Pclp | Process |
0 | Pre-clipping with left / right inversion |
1 | No pre-clipping, left / right inversion: |
Figure 6.6 Pre-clipping
