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★ HARDWARE Manual ★ VDP2 User's Manual ★ Chapter 12 Color calculation
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VDP2 User's Manual/Chapter 12 Color Calculation

●Normal color calculation

There are two types of modes when performing color calculations on the top image and second image:

  1. The top image and second image are added according to the color calculation ratio value.
  2. Top image and second image are added as they are.

When using the color calculation mode that adds according to the color calculation ratio value, set the color calculation ratio value for each screen in the register. The color calculation ratio for sprites can be specified for each character, one out of a maximum of eight register values, and the color calculation ratio for the scroll screen can be specified in one register for each surface. For information on sprite color calculation ratios, refer to ` `●Color calculation ratio register '' in ` `9.2 Priority and color calculations ''.

The color calculation ratio for each screen can be specified using 5 bits, and a total of 32 levels (top image: second image = 31:1 to 0:32) can be specified.The mode for specifying the ratio value is as follows. There are two types.

  1. Specify on the top image side
  2. Specify on the second image side

If specified on the top image side, the color calculation ratio value of the sprite that became the top image or the scroll screen will be used regardless of the second image screen. Also, when specifying on the second image side, the color calculation ratio can be changed depending on the screen of the second image, and the color calculation ratio value of not only the sprite and scroll screen but also the line color screen and back screen is used.

When using the color calculation mode that adds values as they are, you can create an effect where the top image fades in on top of the second image by gradually rewriting the color data of the top image from 00H to the original color. Masu. However, please note that at the same time, the resulting color will be brighter than it originally was. If the addition result exceeds FFH, it is assumed to be FFH. Figure 12.2 shows the color calculation ratio mode.

Figure 12.2 Color calculation ratio mode

Color calculations can be performed without restrictions when the TV screen mode is normal mode, but when the TV screen mode is high resolution mode or dedicated monitor mode, there are restrictions depending on the color RAM mode and the color format of the second image. Table 12.1 shows the limitations of color calculation functions.

Table 12.1 Color calculation functions in high resolution mode or dedicated monitor mode
 Color RAM mode
 Color format of second image
 Color calculation function
mode 0 Palette format or RGB format ○ Can be used
mode 1 pallet format × Not available
RGB format ○ Can be used
mode 2 pallet format × Not available
RGB format ○ Can be used

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★ HARDWARE Manual ★ VDP2 User's Manual ★ Chapter 12 Color calculation
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