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1.4 Priority function

VDP2 has four priority functions: priority function, color calculation function, color offset function, and shadow function.

● Priority function

The display priority of the sprite and scroll screen is determined by the size of a 3-bit value called the priority number.
∙ Up to 8 priority values ​​can be set for the sprite priority number, one of which is specified in character units.
[Normally, the priority number of the scroll screen is specified in units of faces. When using the special priority function, it can be changed in character units or dot units.

Color calculation function

The color calculation function is a function that adds the color data of multiple screens so that the back screen can be seen through the front screen. Normally, the top image and the second image are displayed on two screens, but if the extended color calculation function is used, it can be performed on up to four screens.
∙ Whether or not to perform color calculation is usually specified in units of faces. Sprites can also be specified in character units by setting sprite color calculation conditions. The scroll screen can be specified in character units or dot units using the special color calculation function.
The color calculation ratio between the top image and the second image can be specified from 32 levels. A sprite can set up to eight color calculation ratios, one of which is specified in character units. The scroll screen is specified in units of planes.
⿟ Using the blur calculation function, it is possible to display a specified screen with a horizontal blur.

Color offset function

Color offset function is a function that displays the offset value added (subtracted) to the color data on the screen, and is used for fade-in and fade-out. Whether or not to use the color offset function can be specified in units of faces.
∙ Up to two color offset values ​​can be set for each RGB, and which one to use can be specified in units of planes.

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