main.c File Reference

Pseudo-hires: a 50 % blend of two layers without colour math. More...

#include <snes.h>
#include <snes/tile.h>

Macros
#define	MAP_PAL1   0x0400
	Tilemap entry bits: palette 1 (CGRAM 16-31).
#define	VRAM_BG1_MAP   0x2000
#define	VRAM_BG2_MAP   0x2400
#define	VRAM_CHR   0x0000
	VRAM word addresses: shared char block, the two maps.

Functions
int	main (void)

Variables
u16	bg2_x
	Probe oracle: BG2's horizontal scroll.
static u16	maprow [32]
	One tilemap row being built.
static const u16	palettes [32]
	BG palettes 0 and 1: transparent + red, transparent + blue.
u8	ph_on
	Probe oracle: 1 while pseudo-hires is on.
static u8	px [64]
	One tile's pixels and its 4bpp encoding.
static u8	tilebuf [32]

Detailed Description

Pseudo-hires: a 50 % blend of two layers without colour math.

SETINI bit 3 (pseudo-hires) makes the PPU output 512 pixels per line in any BG mode, taking every other one from the sub screen: the sub screen fills the even columns, the main screen the odd ones. A CRT on composite blurs the two neighbours together, so what you see is a half-and-half blend — the effect some games used for transparency, with colour math left free for something else.

Here BG1 (red horizontal bars) is on the main screen and BG2 (blue vertical bars, scrolling) on the sub screen. Colour math is off: without pseudo-hires the sub screen is not shown at all. Press A to toggle it.

SNES Concepts

• SETINI ($2133) bit 3 through videoSetPseudoHires() (the lib keeps a shadow of the write-only register)
• Main screen / sub screen designation (setMainScreen, setSubScreen) without colour math: the sub screen is only seen through pseudo-hires
• The interleave: sub screen on even columns, main screen on odd ones
• Tiles built at run time (tileEncode4bpp), no asset file

What to Observe

• Purple where the bars cross, half-bright red and blue elsewhere (the emulator's 256-pixel view averages each pixel pair, like a CRT).
• Press A: pseudo-hires off, only the red bars remain; press A again.
• With an emulator's native 512-pixel output (luna --native-res), the alternating columns are visible one by one.

Modules Used

console (videoSetPseudoHires), dma, background, input, tile

See also

video.h (videoSetPseudoHires), docs/tutorials/colormath.md

Macro Definition Documentation

MAP_PAL1

#define MAP_PAL1   0x0400

Tilemap entry bits: palette 1 (CGRAM 16-31).

VRAM_BG1_MAP

#define VRAM_BG1_MAP   0x2000

VRAM_BG2_MAP

#define VRAM_BG2_MAP   0x2400

VRAM_CHR

#define VRAM_CHR   0x0000

VRAM word addresses: shared char block, the two maps.

Function Documentation

main()

int main

(

void

)

Variable Documentation

bg2_x

u16 bg2_x

Probe oracle: BG2's horizontal scroll.

maprow

u16 maprow[32]

static

One tilemap row being built.

palettes

const u16 palettes[32]

static

Initial value:

                          = {
    RGB(0, 0, 0), RGB(31, 4, 4), 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    RGB(0, 0, 0), RGB(6, 10, 31), 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
}

BG palettes 0 and 1: transparent + red, transparent + blue.

ph_on

u8 ph_on

Probe oracle: 1 while pseudo-hires is on.

px

u8 px[64]

static

One tile's pixels and its 4bpp encoding.

tilebuf

u8 tilebuf[32]

static