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★ SGL User's Manual ★ PROGRAMMER'S TUTORIAL
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8-3. Screen mode

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

Table 8-1 Screen mode

 display device
 TV screen mode
 graphic mode
 interlaced mode
 Resolution: vertical x horizontal
 (pixel)
NTSC method normal Graphic A non-interlaced 320×224
320×240
interlace 320×448
320×480
Graphic B non-interlaced 352×224
352×240
interlace 352×448
352×480
high resolution Graphic A non-interlaced 640×224
640×240
interlace 640×448
640×480
Graphic B non-interlaced 704×224
704×240
interlace 704×448
704×480

note)
The default value of the screen mode is 320 horizontal x 224 vertical.

For details on screen modes, 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" also performs initialization and initial settings other than scrolling, but for details, please refer to the default list at the end of the reference manual "Function Reference".

[void slInitSystem ( Uint16 type , TEXTURE *texptr , Uint16 cnt ) ;]
Initialize various settings including scrolling, set screen mode, and set drawing processing unit.
Assign the #define value representing the screen mode, the start address of the memory where the texture is stored (NULL if the texture is not used), and an integer value (1 to 127) representing the screen processing unit to the parameters.
The default value is a resolution of 320 pixels wide x 224 pixels high.
In addition, the mode with a resolution of 352 pixels wide x 240 pixels high cannot be displayed on a regular TV monitor because the resolution is insufficient. The mode with a resolution of 352 pixels wide x 240 pixels high can only be fully displayed when using a monitor that can input RGB.

Table 8-2 “slInitSystem” parameter substitution value example (TV_MODE)
Resolution (pixels)
Width 320 x Height 224 Width 352 x Height 240
Substitution value TV_320x224 TV_352x240

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

If the resolution is 320 x 224 pixels (non-interlaced), no texture, and drawing processing unit: 1 (1/60 second), the function “slInitSystem” will be as shown below.

＜ Figure 8-4 Example of using the function “slInitSystem”＞
●System initialization●


slInitSystem(TV_320x224,NULL,1);
             |          |    |
             |          |    Drawing processing unit: 1 (1/60 seconds)
             |          No texture
             Resolution: 320 x 224 pixels

About drawing processing units

Setting the drawing processing unit in the parameters means specifying the time interval at which the image is rewritten.
For SGL, one drawing processing unit is 1/60 seconds for non-interlaced and 1/30 seconds for double-dense interlace, and can be set in the range of 1 to 127.
The longer the rewriting interval, the more calculation processing can be performed, but because the drawing interval is long, it will look awkward if consecutive images are drawn.
Conversely, if the rewriting interval is short, smooth images can be achieved, but the amount of calculations that can be processed at one time will be reduced.

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★ SGL User's Manual ★ PROGRAMMER'S TUTORIAL
Copyright SEGA ENTERPRISES, LTD., 1997