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8-3. Screen mode

The screen mode is for determining the screen resolution, screen size, display device, etc. Sega Saturn supports a variety of screen modes, but SGL uses and supports the following 16 screen modes.

Table 8-1 Screen modes

Note) The default value of screen mode is 320 x 224 mode.

For details on the screen mode, refer to “HARDWARE MANUAL vol.2: VDP2 User's Manual”.

In SGL, use the library function “slInitSystem” to initialize scrolling and set the screen mode.
This function “slInitSystem” performs initialization and initial settings other than scrolling. For details, refer to the default list at the end of the “Function Reference” volume in the Reference Manual.

[void slInitSystem (Uint16 type, TEXTURE * texptr, Uint16 cnt);]

Initializes various settings including scrolling, screen mode settings, and drawing processing unit settings.
For the parameter, substitute the #define value indicating the screen mode, the start address of the memory where the texture is stored (NULL if texture is not used), and the integer value (1-127) indicating the screen processing unit.
The default value is the mode of resolution and horizontal 320 x vertical 224 pixels.
Also, the mode of resolution and horizontal 352 x vertical 240 pixels cannot be displayed because the resolution is insufficient on a normal TV monitor. The mode of resolution and horizontal 352 x vertical 240 pixels can be displayed completely only when using a monitor capable of RGB input.

Table 8-2 “slInitSystem” parameter substitution value example (TV_MODE)

Note) The values ​​in the above table are defined in “sl_def.h”.

When the resolution is 320 x 224 pixels (non-interlace), no texture, and the rendering processing unit is 1 (1/60 second), the function “slInitSystem” is as shown below.

Figure 8-4 Example of using function “slInitSystem”

About drawing processing units

The setting of the drawing processing unit in the parameter means the time interval for rewriting the image.
For SGL, 1/60 seconds can be set for non-interlace and 1/30 seconds for double-dense interlace can be set in the range of 1 to 127.
The longer the rewrite interval, the more computation processing can be performed, but the drawing interval is long, so when you draw consecutive images, it looks awkward.
Conversely, if the rewrite interval is short, smooth images can be realized, but the amount of computation that can be processed at one time is reduced.

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