static GGLContext *gr_context = 0;
static GGLSurface gr_framebuffer[2];
static unsigned gr_active_fb = 0;
static int gr_fb_fd = -1;
static int gr_vt_fd = -1;
static struct fb_var_screeninfo vi;
struct fb_fix_screeninfo fi;
// 得到framebuffer的相关信息（可变或固定的）
// 及映射数据区域
static int get_framebuffer(GGLSurface *fb)
{
int fd;
void *bits;
//将尝试打开两个位置的设备文件
fd = open("/dev/graphics/fb0", O_RDWR);
if (fd < 0) {
printf("cannot open /dev/graphics/fb0, retrying with /dev/fb0\n");
if ((fd = open("/dev/fb0", O_RDWR)) < 0) {
perror("cannot open /dev/fb0");
return -1;
}
}
//得到framebuffer的相关信息
if(ioctl(fd, FBIOGET_FSCREENINFO, &fi) < 0) {
perror("failed to get fb0 info");
return -1;
}
if(ioctl(fd, FBIOGET_VSCREENINFO, &vi) < 0) {
perror("failed to get fb0 info");
return -1;
}
dumpinfo(&fi, &vi);
// kernel缓冲区映射到用户空间
bits = mmap(0, fi.smem_len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if(bits == MAP_FAILED) {
perror("failed to mmap framebuffer");
return -1;
}
fb->version = sizeof(*fb);
fb->width = vi.xres;
fb->height = vi.yres;
fb->stride = fi.line_length / (vi.bits_per_pixel >> 3);
fb->data = bits;
fb->format = GGL_PIXEL_FORMAT_RGB_565;
// 双缓冲
fb++;
fb->version = sizeof(*fb);
fb->width = vi.xres;
fb->height = vi.yres;
fb->stride = fi.line_length / (vi.bits_per_pixel >> 3);
fb->data = (void*) (((unsigned) bits) + vi.yres * vi.xres * 2);
fb->format = GGL_PIXEL_FORMAT_RGB_565;
return fd;
}
// 这里假设framebuffer是双缓冲，理论上应当判断下
// 不能直接断定是否双缓冲
static void set_active_framebuffer(unsigned n)
{
if(n > 1) return;
// framebuffer的缓冲区大小，至少要可以两张图片的容量
vi.yres_virtual = vi.yres * 2;
vi.yoffset = n * vi.yres;
if(ioctl(gr_fb_fd, FBIOPUT_VSCREENINFO, &vi) < 0) {
fprintf(stderr,"active fb swap failed!\n");
} else
printf("active buffer: %d\n", n);
}
// 导出framebuffer的相关信息（x, y , bits_per_pixel等）
static void dumpinfo(struct fb_fix_screeninfo *fi, struct fb_var_screeninfo *vi)
{
fprintf(stderr,"vi.xres = %d\n", vi->xres);
fprintf(stderr,"vi.yres = %d\n", vi->yres);
fprintf(stderr,"vi.xresv = %d\n", vi->xres_virtual);
fprintf(stderr,"vi.yresv = %d\n", vi->yres_virtual);
fprintf(stderr,"vi.xoff = %d\n", vi->xoffset);
fprintf(stderr,"vi.yoff = %d\n", vi->yoffset);
fprintf(stderr, "vi.bits_per_pixel = %d\n", vi->bits_per_pixel);
fprintf(stderr, "fi.line_length = %d\n", fi->line_length);
}
int gr_init(void)
{
int fd = -1;
// 不太明白，为什么要打开tty0,测试的时候不执行也没有影响
if (!access("/dev/tty0", F_OK)) {
fd = open("/dev/tty0", O_RDWR | O_SYNC);
if(fd < 0)
return -1;
if(ioctl(fd, KDSETMODE, (void*) KD_GRAPHICS)) {
close(fd);
return -1;
}
}
//初始化，framebuffer 数据结构
gr_fb_fd = get_framebuffer(gr_framebuffer);
if(gr_fb_fd < 0) {
if (fd >= 0) {
ioctl(fd, KDSETMODE, (void*) KD_TEXT);
close(fd);
}
return -1;
}
gr_vt_fd = fd;
/* start with 0 as front (displayed) and 1 as back (drawing) */
gr_active_fb = 0;
set_active_framebuffer(0);
return 0;
}
// 退出，关闭文件等
void gr_exit(void)
{
close(gr_fb_fd);
gr_fb_fd = -1;
if (gr_vt_fd >= 0) {
ioctl(gr_vt_fd, KDSETMODE, (void*) KD_TEXT);
close(gr_vt_fd);
gr_vt_fd = -1;
}
}
int gr_fb_width(void)
{
return gr_framebuffer[0].width;
}
int gr_fb_height(void)
{
return gr_framebuffer[0].height;
}
uint16_t red = 0xf800;
uint16_t green = 0x07e0;
uint16_t blue = 0x001f;
// 在缓冲区上绘制图片，一共四个区域
|--|--|
| | |
|--|--|
| | |
-----
void draw_grid(int w, int h, uint16_t* loc) {
int i, j;
int v;
int stride = fi.line_length / (vi.bits_per_pixel >> 3);
for (j = 0; j < h/2; j++) {
for (i = 0; i < w/2; i++)
loc[i + j*(stride)] = red;
for (; i < w; i++)
loc[i + j*(stride)] = green;
}
for (; j < h; j++) {
for (i = 0; i < w/2; i++)
loc[i + j*(stride)] = blue;
for (; i < w; i++)
loc[i + j*(stride)] = 0xffff;
}
}
// 清空缓冲区数据都为00，视觉上表现为纯黑色
void clear_screen(int w, int h, uint16_t* loc)
{
int i,j;
int stride = fi.line_length / (vi.bits_per_pixel >> 3);
for (j = 0; j < h; j++)
for (i = 0; i < w; i++)
loc[i + j*(stride)] = 0x0000;
}
int main(int argc, char **argv) {
int w;
int h;
int id = 0;
gr_init();
w = vi.xres;
h = vi.yres;
// 清空缓冲区数据都为00
clear_screen(w, h, (uint16_t *)gr_framebuffer[0].data);
clear_screen(w, h, (uint16_t *)gr_framebuffer[1].data);
if (argc > 2) {
w = atoi(argv[1]);
h = atoi(argv[2]);
}
if (argc > 3)
id = !!atoi(argv[3]);
// 绘制图片
draw_grid(w, h, (uint16_t *)gr_framebuffer[id].data);
//显示双缓冲的内容，中间和最后加个sleep(),效果会更明显
set_active_framebuffer(!id);
set_active_framebuffer(id);
return 0;
}