虽然现在能通过交叉环境编译程序，并push到Android上执行，但那只是console台程序，是不是有些单调呢？下面就要看如何通过Linux的
framebuffer
技术在Android上画图形，关于Linux的framebuffer技术，这里就不再详细讲解了，请大家google一下。
操作framebuffer的主要步骤如下：
1、打开一个可用的FrameBuffer设备；
2、通过mmap调用把显卡的物理内存空间映射到用户空间；
3、更改内存空间里的像素数据并显示；
4、退出时关闭framebuffer设备。
下面的这个例子简单地用framebuffer画了一个渐变的进度条，代码 framebuf.c 如下：
#include
#include
#include
#include
#include
inline static unsigned short int make16color(unsigned char r,
unsigned char g, unsigned char b)
{
return
(
(((r >> 3)
& 31) << 11) |
(((g >> 2)
& 63) <<
5) |
((b >> 3)
&
31)
);
}
int main() {
int fbfd =
0;
struct
fb_var_screeninfo vinfo;
struct
fb_fix_screeninfo finfo;
long int
screensize = 0;
char *fbp = 0;
int x = 0, y
= 0;
int
guage_height = 20, step = 10;
long int
location = 0;
// Open
the file for reading and writing
fbfd =
open("/dev/graphics/fb0", O_RDWR);
if (!fbfd)
{
printf("Error: cannot open framebuffer device.\n");
exit(1);
}
printf("The
framebuffer device was opened successfully.\n");
// Get
fixed screen information
if
(ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
printf("Error reading fixed information.\n");
exit(2);
}
// Get
variable screen information
if
(ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
printf("Error reading variable information.\n");
exit(3);
}
printf("sizeof(unsigned short) = %d\n",
sizeof(unsigned short));
printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres,
vinfo.bits_per_pixel );
printf("xoffset:%d, yoffset:%d, line_length:
%d\n", vinfo.xoffset, vinfo.yoffset, finfo.line_length );
// Figure
out the size of the screen in bytes
screensize =
vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;;
// Map
the device to memory
fbp = (char
*)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
fbfd, 0);
if
((int)fbp == -1) {
printf("Error: failed to map framebuffer device to
memory.\n");
exit(4);
}
printf("The
framebuffer device was mapped to memory successfully.\n");
//set to black color first
memset(fbp, 0, screensize);
//draw
rectangle
y =
(vinfo.yres - guage_height) / 2 -
2;
// Where we are going to put the pixel
for (x =
step - 2; x < vinfo.xres - step + 2; x++) {
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
(y+vinfo.yoffset) * finfo.line_length;
*((unsigned short int*)(fbp + location)) = 255;
}
y =
(vinfo.yres + guage_height) / 2 +
2;
// Where we are going to put the pixel
for (x =
step - 2; x < vinfo.xres - step + 2; x++) {
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
(y+vinfo.yoffset) * finfo.line_length;
*((unsigned short int*)(fbp + location)) = 255;
}
x = step
- 2;
for (y =
(vinfo.yres - guage_height) / 2 - 2; y < (vinfo.yres
+ guage_height) / 2 + 2; y++) {
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
(y+vinfo.yoffset) * finfo.line_length;
*((unsigned short int*)(fbp + location)) = 255;
}
x =
vinfo.xres - step + 2;
for (y =
(vinfo.yres - guage_height) / 2 - 2; y < (vinfo.yres
+ guage_height) / 2 + 2; y++) {
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
(y+vinfo.yoffset) * finfo.line_length;
*((unsigned short int*)(fbp + location)) = 255;
}
// Figure
out where in memory to put the pixel
for ( x =
step; x < vinfo.xres - step; x++ ) {
for ( y = (vinfo.yres - guage_height) / 2; y <
(vinfo.yres + guage_height) / 2; y++ ) {
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
(y+vinfo.yoffset) * finfo.line_length;
if ( vinfo.bits_per_pixel == 32 ) {
*(fbp + location) =
100;
// Some blue
*(fbp + location + 1) =
15+(x-100)/2;
// A little green
*(fbp + location + 2) =
200-(y-100)/5;
// A lot of red
*(fbp + location + 3) =
0;
// No transparency
} else { //assume 16bpp
unsigned char b = 255 * x / (vinfo.xres - step);
unsigned char g =
255;
// (x - 100)/6 A little green
unsigned char r =
255; // A lot
of red
unsigned short int t = make16color(r, g, b);
*((unsigned short int*)(fbp + location)) = t;
}
}
//printf("x = %d, temp = %d\n",
x, temp);
//sleep to see it
usleep(200);
}
//clean
framebuffer
munmap(fbp,
screensize);
close(fbfd);
return
0;
}
注意，在Android环境，framebuffer设备不是象linux一样的 /dev/fb0，而是 /dev/graphics/fb0 ，
fbfd = open("/dev/graphics/fb0", O_RDWR);
打开framebuffer设备，
fbp =
(char *)mmap(0, screensize, PROT_READ | PROT_WRITE,
MAP_SHARED,
fbfd, 0);
将设备map到一块内存，然后就可以操作这块内存空间来显示你想画的图形了。
最后别忘了关闭设备：
munmap(fbp, screensize);
close(fbfd);
效果图如下：
![]()
