nes 红白机模拟器 第1篇

对比了很多种，开源的 NES 模拟器 VirtuaNES , nestopia , FakeNES , FCEUX , InfoNES , LiteNES

最后决定使用 LiteNES 进行移值，它是由 mynes 移值而来。LiteNES 对 mynes 代码进行整理兼容了 C99 标准，编译时无警告。

https://github.com/NJUOS/LiteNES

https://github.com/yaglo/mynes

LiteNES , mynes  基于 Allegro ，Allegro 是一种提供底层画图，输入，定时器等支持的库。

LiteNES 全部抽象提取代码到 一个 hal.c 文件里面，修改移值十分方便。下面是修改后的样子，替换这个文件。

在修改下 Makefile 中的 gcc 改为 arm-linux-gcc 编译 即可在板子上出现 Game 画面了（经过测试，发现支持的游戏不多，有的载加不出来）

NES 移值第1篇，仅能出现画面。以后会更新添加声音，多线程，输入等。现在只为能显示出画面。

hal.c :

/*
This file present all abstraction needed to port LiteNES.
  (The current working implementation uses allegro library.)

To port this project, replace the following functions by your own:
1) nes_hal_init()
    Do essential initialization work, including starting a FPS HZ timer.

2) nes_set_bg_color(c)
    Set the back ground color to be the NES internal color code c.

3) nes_flush_buf(*buf)
    Flush the entire pixel buf's data to frame buffer.

4) nes_flip_display()
    Fill the screen with previously set background color, and
    display all contents in the frame buffer.

5) wait_for_frame()
    Implement it to make the following code is executed FPS times a second:
        while (1) {
            wait_for_frame();
            do_something();
        }

6) int nes_key_state(int b) 
    Query button b's state (1 to be pressed, otherwise 0).
    The correspondence of b and the buttons:
      0 - Power
      1 - A
      2 - B
      3 - SELECT
      4 - START
      5 - UP
      6 - DOWN
      7 - LEFT
      8 - RIGHT
*/
#include "hal.h"
#include "fce.h"
#include "common.h"

/**
 * allegro API 不明白的看文档 
 * https://www.allegro.cc/manual/5/index.html
 */
/* lcd 操作相关 头文件 */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <string.h>
#include <sys/mman.h>

static int fb_fd;
static unsigned char *fb_mem;
static int px_width;
static int line_width;
static int screen_width;
static struct fb_var_screeninfo var;

static int lcd_fb_display_px(int color, int x, int y)
{
    unsigned char  *pen8;
    unsigned short *pen16;
    
    unsigned char r,g,b;
    
    pen8 = (unsigned char *)(fb_mem + y*line_width + x*px_width);
    pen16 = (unsigned short *)pen8;
    
    //合并为 565 格式 16bbp
    r = (color>>16) & 0xff;
    g = (color>>8) & 0xff;
    b = (color>>0) & 0xff;
    *pen16 = (r>>3)<<11 | (g>>2)<<5 | (b>>3);
    
    return 0;
}

//调色板转16进行32位颜色
static int pal2color(pal pal)
{
    int color = 0;
    color = pal.r << 16 | pal.g <<8 | pal.b;
    return color;
}

static int lcd_fb_init()
{
    //如果使用 mmap 打开方式 必须是 读写方式
    fb_fd = open("/dev/fb0", O_RDWR);
    if(-1 == fb_fd)
    {
        printf("cat't open /dev/fb0 
");
        return -1;
    }
    //获取屏幕参数
    if(-1 == ioctl(fb_fd, FBIOGET_VSCREENINFO, &var))
    {
        close(fb_fd);
        printf("cat't ioctl /dev/fb0 
");
        return -1;
    }
    //计算参数
    px_width = var.bits_per_pixel / 8;
    line_width = var.xres * px_width;
    screen_width = var.yres * line_width;
    
    fb_mem = (unsigned char *)mmap(NULL, screen_width, PROT_READ | PROT_WRITE, MAP_SHARED, fb_fd, 0);
    if(fb_mem == (void *)-1)
    {
        close(fb_fd);
        printf("cat't mmap /dev/fb0 
");
        return -1;
    }
    //清屏
    memset(fb_mem, 0 , screen_width);
    return 0;
}
  
/* Wait until next allegro timer event is fired. */
void wait_for_frame()
{
    //休眠 FPS = 60 * 1000 毫秒
    usleep(1/FPS*1000);
}

/* Set background color. RGB value of c is defined in fce.h */
void nes_set_bg_color(int c)
{
    //画背景颜色
    int i,j;
    for(i=0; i<SCREEN_WIDTH; i++)
    {
        for(j=0; j<SCREEN_HEIGHT; j++)
        {
            lcd_fb_display_px(pal2color(palette[c]), i, j);
        }
    }    
}

/* Flush the pixel buffer */
void nes_flush_buf(PixelBuf *buf)
{
    Pixel *p;
    int i,x,y,color;
    for (i = 0; i < buf->size; i++) 
    {
           p = &buf->buf[i];
           x = p->x;
        y = p->y;

        color = pal2color(palette[p->c]);
        lcd_fb_display_px(color, x, y);    
        lcd_fb_display_px(color, x+1, y);
        lcd_fb_display_px(color, x, y+1);
        lcd_fb_display_px(color, x+1, y+1);
        }
}

/* Initialization:
   (1) start a 1/FPS Hz timer. 
   (2) register fce_timer handle on each timer event */
void nes_hal_init()
{
    /**
     * 需要完成的事情
     * 1,初始化 lcd 
     * 2,初始化 定时器 先做简单的直接用系统延时
     */
    if(-1 == lcd_fb_init())
    {
        printf("lcd fb init error 
");
        return ;
    }    
}

/* Update screen at FPS rate by allegro's drawing function. 
   Timer ensures this function is called FPS times a second. */
void nes_flip_display()
{
    //设置64种颜色值 不必设置
}

/* Query a button's state.
   Returns 1 if button #b is pressed. */
int nes_key_state(int b)
{
    switch (b)
    {
        case 0: // On / Off
            return 1;
        case 1: // A
            return 1;
        case 2: // B
            return 1;
        case 3: // SELECT
            return 1;
        case 4: // START
            return 1;
        case 5: // UP
            return 1;
        case 6: // DOWN
            return 1;
        case 7: // LEFT
            return 1;
        case 8: // RIGHT
            return 1;
        default:
            return 1;
    }
}