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

●Frame buffer rotation readout

Frame buffer rotation reading is performed using rotation parameter A: screen screen start coordinates (Xst, Yst), screen screen vertical direction coordinate increment (DXst, DYst), and screen screen horizontal direction coordinate increment (DX, DY).
If you display the image specified by rotation parameter A on the rotating scroll screen, you can rotate the entire sprite and the rotating scroll screen in the same way.
If you display the image specified by rotation parameter B on the rotating scroll screen, you can rotate the entire sprite and the rotating scroll screen separately.

The display coordinate value of the frame buffer is calculated from the display coordinate of the left end of the line, which is calculated for each line from the screen screen start coordinate and the screen screen vertical direction coordinate increment, and the horizontal direction coordinate increment of that line.
At this time, from the coordinate range of the frame buffer, the display coordinate value of the left end of the line is a total of 20 bits (sign + 10 bits of the integer part + 9 bits of the decimal part), and the horizontal coordinate increment is the sign + 2 bits of the integer part + 9 bits of the decimal part. It is calculated by rounding down the bits so that there is a total of 12 bits.

In order to read frame buffer rotation using rotation parameter A, the TV mode of VDP1 must be set to rotation 16 or rotation 8. For more information, see the VDP1 User's Manual .

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