爲方便以後學習和工作,現轉載一批文章,方便以後使用。
來源:http://blog.sina.com.cn/s/blog_4a0a39c30100auh9.html 作者:風子
如對Android原生(Natvie)C開發還任何疑問,請參閱《Android原生(Native)C開發之一:環境搭建篇》:http://blog.sina.com.cn/s/blog_4a0a39c30100auh9.html (或者http://android-sz.iteye.com/blog/828246)
雖然現在能通過交叉環境編譯程序,並push到Android上執行,但那只是console臺程序,是不是有些單調呢?下面就要看如何通過Linux的 framebuffer 技術在Android上畫圖形,關於Linux的framebuffer技術,這裏就不再詳細講解了,請大家google一下。
操作framebuffer的主要步驟如下:
1、打開一個可用的FrameBuffer設備;
2、通過mmap調用把顯卡的物理內存空間映射到用戶空間;
3、更改內存空間裏的像素數據並顯示;
4、退出時關閉framebuffer設備。
下面的這個例子簡單地用framebuffer畫了一個漸變的進度條,代碼 framebuf.c 如下:
#include <unistd.h> #include <stdio.h> #include <fcntl.h> #include <linux/fb.h> #include <sys/mman.h> 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環境,framebuffer設備不是象linux一樣的 /dev/fb0,而是 /dev/graphics/fb0 ,
fbfd = open("/dev/graphics/fb0", O_RDWR);
打開framebuffer設備,
fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
fbfd, 0);
將設備map到一塊內存,然後就可以操作這塊內存空間來顯示你想畫的圖形了。
最後別忘了關閉設備:
munmap(fbp, screensize);
close(fbfd);
效果圖如下: