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Proper (I believe) emulation of most GameBoy Camera registers

This commit is contained in:
Lior Halphon 2016-10-03 14:22:54 +03:00
parent 2a84d62187
commit dd23fffcc0
2 changed files with 37 additions and 13 deletions
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41
Core/camera.c
View File

@ -2,7 +2,7 @@
uint8_t GB_camera_read_image(GB_gameboy_t *gb, uint16_t addr) uint8_t GB_camera_read_image(GB_gameboy_t *gb, uint16_t addr)
{ {
if (gb->camera_registers[0]) { if (gb->camera_registers[GB_CAMERA_FLAGS] & 1) {
/* Forbid reading the image while the camera is busy. */ /* Forbid reading the image while the camera is busy. */
return 0xFF; return 0xFF;
} }
@ -16,19 +16,33 @@ uint8_t GB_camera_read_image(GB_gameboy_t *gb, uint16_t addr)
for (uint8_t x = tile_x * 8; x < tile_x * 8 + 8; x++) { for (uint8_t x = tile_x * 8; x < tile_x * 8 + 8; x++) {
int color = gb->camera_get_pixel_callback? gb->camera_get_pixel_callback(gb, x,y) ^ 0xFF : (rand() & 0xFF); long color = gb->camera_get_pixel_callback? gb->camera_get_pixel_callback(gb, x,y) : (rand() & 0xFF);
/* Dither using a pattern */ /* Color is multiplied by the multiplier register. */
color += ((x + y) & 1? 21 : -21) >> (y & 1); /* It is unknown what register 1 does, but changing bits 2-3 from 0x4 to 0x8 seems equivalent to adding 0x2000
if (color > 255) { to the multiplier. Is it related to actual exposure time? */
color = 255; unsigned long multiplier_bias = (gb->camera_registers[GB_CAMERA_UNKNOWN_FLAGS] & 0xF) * 0x800;
color = color * ((gb->camera_registers[GB_CAMERA_MULTIPLIER_HIGH] << 8) + gb->camera_registers[GB_CAMERA_MULTIPLIER_LOW] + multiplier_bias) / 0x3000;
/* The camera's registers are used as a threshold pattern, which defines the dithering */
uint8_t pattern_base = ((x & 3) + (y & 3) * 4) * 3 + GB_CAMERA_DITHERING_PATTERN_START;
/* Todo: I have absolutely no reason to assume that this does not go backwards! */
if (color < gb->camera_registers[pattern_base]) {
color = 3;
} }
else if (color < 0) { else if (color < gb->camera_registers[pattern_base + 1]) {
color = 2;
}
else if (color < gb->camera_registers[pattern_base + 2]) {
color = 1;
}
else {
color = 0; color = 0;
} }
ret <<= 1; ret <<= 1;
ret |= (color >> (6 + bit)) & 1; ret |= (color >> bit) & 1;
} }
return ret; return ret;
@ -46,22 +60,23 @@ void GB_set_camera_update_request_callback(GB_gameboy_t *gb, GB_camera_update_re
void GB_camera_updated(GB_gameboy_t *gb) void GB_camera_updated(GB_gameboy_t *gb)
{ {
gb->camera_registers[0] = 0; gb->camera_registers[GB_CAMERA_FLAGS] &= ~1;
} }
void GB_camera_write_register(GB_gameboy_t *gb, uint16_t addr, uint8_t value) void GB_camera_write_register(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
{ {
addr &= 0x7F; addr &= 0x7F;
if (addr == 0) { if (addr == GB_CAMERA_FLAGS) {
if ((value & 1) && gb->camera_update_request_callback) { if ((value & 1) && !(gb->camera_registers[GB_CAMERA_FLAGS] & 1) && gb->camera_update_request_callback) {
/* If no callback is set, ignore the write as if the camera is instantly done */ /* If no callback is set, ignore the write as if the camera is instantly done */
gb->camera_registers[0] = 1; gb->camera_registers[GB_CAMERA_FLAGS] |= 1;
gb->camera_update_request_callback(gb); gb->camera_update_request_callback(gb);
} }
} }
else { else {
if (addr >= 0x36) { if (addr >= 0x36) {
GB_log(gb, "Wrote invalid camera register %02x: %2x\n", addr, value); GB_log(gb, "Wrote invalid camera register %02x: %2x\n", addr, value);
return;
} }
/* Todo: find out what these registers do */ /* Todo: find out what these registers do */
gb->camera_registers[addr] = value; gb->camera_registers[addr] = value;
@ -70,7 +85,7 @@ void GB_camera_write_register(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
uint8_t GB_camera_read_register(GB_gameboy_t *gb, uint16_t addr) uint8_t GB_camera_read_register(GB_gameboy_t *gb, uint16_t addr)
{ {
if ((addr & 0x7F) == 0) { if ((addr & 0x7F) == 0) {
return gb->camera_registers[0]; return gb->camera_registers[GB_CAMERA_FLAGS];
} }
return 0; return 0;
} }

9
Core/camera.h
View File

@ -2,6 +2,15 @@
#define camera_h #define camera_h
#include "gb.h" #include "gb.h"
enum {
GB_CAMERA_FLAGS = 0,
GB_CAMERA_UNKNOWN_FLAGS = 1,
GB_CAMERA_MULTIPLIER_HIGH = 2,
GB_CAMERA_MULTIPLIER_LOW = 3,
GB_CAMERA_DITHERING_PATTERN_START = 6,
GB_CAMERA_DITHERING_PATTERN_END = 0x35,
};
uint8_t GB_camera_read_image(GB_gameboy_t *gb, uint16_t addr); uint8_t GB_camera_read_image(GB_gameboy_t *gb, uint16_t addr);
void GB_set_camera_get_pixel_callback(GB_gameboy_t *gb, GB_camera_get_pixel_callback_t callback); void GB_set_camera_get_pixel_callback(GB_gameboy_t *gb, GB_camera_get_pixel_callback_t callback);