osViSetMode

#include <ultra64.h> /* os.h
*/ void osViSetMode(OSViMode *mode);

Argument

• mode - VI mode

Return Value
None

Explanation
This function sets the display mode in the VI. The VI supports a total of 56 display modes. These break down into 14 NTSC modes, 14 PAL modes, 14 MPAL modes, and 14 full-screen display PAL (FPAL) modes. The attributes of each mode, such as interlace and non-interlace, 16-bit color pixels and 32-bit color pixels, low-resolution and high-resolution, etc., can be set. In addition, the resolution can be dropped or images can be rescaled in order to increase rendering speed.

The 56 modes are indicated by 5 switches, viz., high/low resolution, 16/32-bit color pixels, anti-aliasing/point sampling, filter/non-filter processing, and NTSC/PAL/MPAL/FPAL format. The defined symbol names for these modes are in <os.h>. For example, "OS_VI_NTSC_LPN1" indicates that low-resolution, point sampling, non-interlace, and 16-bit color pixels are supported, while "OS_VI_PAL_LPN1" indicates that the same content are supported in PAL format.

The last 4 characters of the symbol name (LPN1, etc.) comprise the following codes.

Of the possible combinations of the above codes, the following 14 modes are each supported in NTSC/PAL/FPAL/MPAL:

LPN1, LPF1, LAN1, LAF1, LPN2,
LPF2, LAN2, LAF2, HPN1, HPF1,
HAN1, HAF1, HPN2, HPF2

At low resolution (320 pixels x 240 lines in PAL/MPAL/NTSC modes, 320 pixels x 288 lines in FPAL mode), non-interlaced mode and interlaced mode can be selected. Non-interlaced mode repeats the same frame in each field (scan). In contrast, interlaced mode interpolates between adjacent lines. First, in the first field, the upper line is weighted 75% and the lower line is weighted 25%. Then, interpolation is performed in the next in the next field, by weighting the upper line 25% and weighting the lower line 75%. In this case, there is no flicker because there is not high blanking frequency.

At high resolution (640 pixels x 480 lines in PAL/MPAL/NTSC modes, 640 pixels x 576 lines in FPAL mode), normal interlaced mode and de-flickered interlaced mode can be selected.
In normal interlaced mode, only those data, which have been rendered for that field, are used in one field. While the current field is being displayed, the next field is being rendered, and since they have no effect on one another, there is no need to use a double-buffer. However, since it is high resolution, pixels, which are only displayed in one field, will flicker. On the other hand, in de-flickered interlaced mode, the lines are averaged and displayed to eliminate the high-frequency components. However, the data for both fields are required to display one field in this mode, double-buffer processing becomes necessary.

The register settings for these 56 modes are in the VI mode table osViModeTable, which is defined as an external variable. osViSetMode overwrites all VI registers with data referenced by mode (the pointer to osViModeTable) at the timing of the next vertical retrace. All previous settings (XY scale, gamma correction, etc.) will be reset.

The VI mode table is an array of 56 OSViMode structures, but each mode is individually defined in <os.h> as an external variable in the OS source file.

For instance, there are two ways, as shown below, to write it when registering NTSC, low-resolution, anti-aliasing, non-interlaced processing, and 16-bit mode in the VI.

osViSetMode(&osViModeNtscLan1);
or
osViSetMode(&osViModeTable[OS_VI_NTSC_LAN1]);

Since the latter method is linked to data, which are not used, it uses a lot of memory. It is recommended that the former method be used.

* Please See "Reference (VI Mode Type List)" for the VI mode types.

Cautions
osViSetMode will return all of the settings for functions that are set by X/Y scale processing or osViSetSpecialFeatures (e.g., gamma correction) to their default values as defined in the VI mode table.

References VI Mode Type List

NTSC	OS_VI_NTSC_LPN1	0
	OS_VI_NTSC_LPF1	1
	OS_VI_NTSC_LAN1	2
	OS_VI_NTSC_LAF1	3
	OS_VI_NTSC_LPN2	4
	OS_VI_NTSC_LPF2	5
	OS_VI_NTSC_LAN2	6
	OS_VI_NTSC_LAF2	7
	OS_VI_NTSC_HPN1	8
	OS_VI_NTSC_HPF1	9
	OS_VI_NTSC_HAN1	10
	OS_VI_NTSC_HAF1	11
	OS_VI_NTSC_HPN2	12
	OS_VI_NTSC_HPF2	13
PAL	OS_VI_PAL_LPN1	14
	OS_VI_PAL_LPF1	15
	OS_VI_PAL_LAN1	16
	OS_VI_PAL_LAF1	17
	OS_VI_PAL_LPN2	18
	OS_VI_PAL_LPF2	19
	OS_VI_PAL_LAN2	20
	OS_VI_PAL_LAF2	21
	OS_VI_PAL_HPN1	22
	OS_VI_PAL_HPF1	23
	OS_VI_PAL_HAN1	24
	OS_VI_PAL_HAF1	25
	OS_VI_PAL_HPN2	26
	OS_VI_PAL_HPF2	27
MPAL (Mainly Brazil)	OS_VI_MPAL_LPN1	28
	OS_VI_MPAL_LPF1	29
	OS_VI_MPAL_LAN1	30
	OS_VI_MPAL_LAF1	31
	OS_VI_MPAL_LPN2	32
	OS_VI_MPAL_LPF2	33
	OS_VI_MPAL_LAN2	34
	OS_VI_MPAL_LAF2	35
	OS_VI_MPAL_HPN1	36
	OS_VI_MPAL_HPF1	37
	OS_VI_MPAL_HAN1	38
	OS_VI_MPAL_HAF1	39
	OS_VI_MPAL_HPN2	40
	OS_VI_MPAL_HPF2	41
FPAL (Full-screen PAL)	OS_VI_FPAL_LPN1	42
	OS_VI_FPAL_LPF1	43
	OS_VI_FPAL_LAN1	44
	OS_VI_FPAL_LAF1	45
	OS_VI_FPAL_LPN2	46
	OS_VI_FPAL_LPF2	47
	OS_VI_FPAL_LAN2	48
	OS_VI_FPAL_LAF2	49
	OS_VI_FPAL_HPN1	50
	OS_VI_FPAL_HPF1	51
	OS_VI_FPAL_HAN1	52
	OS_VI_FPAL_HAF1	53
	OS_VI_FPAL_HPN2	54
	OS_VI_FPAL_HPF2	55

Example

//      Start VI manager & blackout
        osCreateViManager(OS_PRIORITY_VIMGR);
#if (SCREEN_WD==320)&&(SCREEN_HT==240)     // Settings for low resolution
        osViSetMode(&osViModeNtscLan1);
#elif (SCREEN_WD==640)&&(SCREEN_HT==480)   // Settings for high resolution
        osViSetMode(&osViModeNtscHaf1);
#else
#error  "Illegal Screen size"
#endif
        osViBlack(TRUE);

See Also
osViGetCurrentMode
osViSetSpecialFeatures

Revision History
2/1/1999 Completely rewritten