★ HARDWARE Manual ★ VDP2 User's Manual ★ Chapter 6 Rotating scroll screen
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VDP2 User's Manual / Chapter 6 Rotating Scroll Screen

● Switching rotation parameters

RBG0 allows you to specify which of the two sets of rotation parameter tables to use, and to partially switch rotation parameters on a single display screen. You can choose how to use the rotation parameters from the following four rotation parameter modes.

Mode 0:
Use rotation parameter A

Mode 1:
Use rotation parameter B

Mode 2:
The image is switched according to the coefficient data read from the coefficient table of rotation parameter A.

Mode 3:
Switch by rotation parameter window

For modes 0 and 1, the images obtained by each set of rotation parameter tables are displayed. In modes 2 and 3, the image obtained by rotation parameter A and the image obtained by rotation parameter B are displayed on one screen.

For mode 2, set the RAKTE bit in the coefficient table control register to 1 to use the coefficient table for rotation parameter A. When the value of the most significant bit of the coefficient data read from the coefficient table is 0, the image obtained by rotation parameter A is displayed, and when it is 1, the image obtained by rotation parameter B is displayed as the image of RBG0. If the coefficient data for rotation parameter A is set to be read dot by dot, the two images can be switched dot by dot, but the coefficient data for rotation parameter B can be read dot by dot. lose.

In mode 3, the rotation parameter window bit in the rotation window control register switches between the two images. When the window is used as a transparency processing window, the image obtained by rotation parameter B is displayed in the part where the screen is cut and made transparent, and the image obtained by rotation parameter A is displayed in the other part of RBG0. Display as an image.

Figure 6.5 shows an example of image display in modes 0 to 3 above.

Figure 6.5 Switching rotation parameters
● When rotation parameter mode is 0 ┏━━━━━━━━━━━━━━┓
┃ ┃
┃ ┃
┃ Rotation parameter A ┃
┃ Obtained image ┃
┃ ┃
┃ ┃
┗━━━━━━━━━━━━━━┛

● In case of rotation parameter mode 1　
┏━━━━━━━━━━━━━━┓
┃ ┃
┃ ┃
┃ Rotation parameter B ┃
┃ Obtained image ┃
┃ ┃
┃ ┃
┗━━━━━━━━━━━━━━┛

● In case of rotation parameter mode 2　
┏━━━━━━━━━━━━━━┓　
┃Rotation parameter A / ┃　
Obtained by ┃ / ┃　
┃Image / ┃　
┃ / Rotational parameter ┃　
┃ / Obtained by B ┃　
┃ / Image ┃　
┗━━━━━━━━━━━━━━┛　
↑↑　
│ From the coefficient table for rotation parameter B │ MSB of the read coefficient data is "0"
│ part　
│　
The part where the MSB of the coefficient data read from the coefficient table for rotation parameter A is "1"　

● In case of rotation parameter mode 3　
Switched and displayed by rotation parameter window　
┏━━━━━━━━━━━━━━┓　
┃┌────────────┐┃　
┃ │ Rotation parameter B │ ← ─ Transparent processing window ┃ │ Obtained image │ ┃ Sometimes the screen is cut out ┃ └ ────────────┘┃ The part to be transparent　
┃ Rotation parameter A ┃　
┃ Obtained image ┃　
┗━━━━━━━━━━━━━━┛　
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★ HARDWARE Manual VDP2 User's Manual ★ Chapter 6 Rotating scroll screen
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