android - 直接在 Android 上写入帧缓冲区

Question

我有一部 Android 4.2.2 的 root 手机。我想在引导加载程序代码中使用 minui API(来源 here)在屏幕上绘制内容。 minui 比 native OpenGL 简单得多，我不需要 OpenGL 公开的任何复杂功能。

问题是我无法直接将内容写入fb0 设备。 FBIOPUT_VSCREENINFO 因未知原因而失败。

如何在 Android 上直接绘制到 fb0，或者如何在引导加载程序模式之外使用 minui？

Answer 1

设备节点:/dev/graphics/fb0

您可以在 Android 树中构建或使用 arm-linux-gcc。

arm-linux-gcc -D__ANDROID__ fb-test.c -static

喜欢普通的嵌入式linux，有一个例子:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>
struct fb_fix_screeninfo FixedInfo;
struct fb_var_screeninfo OrigVarInfo;
static int FrameBufferFD = -1;
void *FrameBuffer = (void *) -1;

#ifndef __ANDROID__
#define FRAMEBUFFER "/dev/fb0"
#else
#define FRAMEBUFFER "/dev/graphics/fb0"
#endif //__ANDROID__

void openFBDEV(void)
{
    /* open the framebuffer device */
    FrameBufferFD = open(FRAMEBUFFER, O_RDWR);
    if (FrameBufferFD < 0)
    {
        fprintf(stderr, "Error opening %s\n", FRAMEBUFFER);
        exit(1);
    }
    /* Get the fixed screen info */
    if (ioctl(FrameBufferFD, FBIOGET_FSCREENINFO, &FixedInfo))
    {
        fprintf(stderr, "error: ioctl(FBIOGET_FSCREENINFO) failed\n");
        exit(1);
    }
    /* get the variable screen info */
    if (ioctl(FrameBufferFD, FBIOGET_VSCREENINFO, &OrigVarInfo))
    {
        fprintf(stderr, "error: ioctl(FBIOGET_VSCREENINFO) failed\n");
        exit(1);
    }

    if (FixedInfo.visual != FB_VISUAL_TRUECOLOR
            && FixedInfo.visual != FB_VISUAL_DIRECTCOLOR)
    {
        fprintf(stderr,
                "non-TRUE/DIRECT-COLOR visuals (0x%x) not supported by this demo.\n",
                FixedInfo.visual);
        exit(1);
    }
    /*
     * fbdev says the frame buffer is at offset zero, and the mmio region
     * is immediately after.
     */
    /* mmap the framebuffer into our address space */
    FrameBuffer = (void *) mmap(0, /* start */
    FixedInfo.smem_len, /* bytes */
    PROT_READ | PROT_WRITE, /* prot */
    MAP_SHARED, /* flags */
    FrameBufferFD, /* fd */
    0 /* offset */);
    if (FrameBuffer == (void *) -1)
    {
        fprintf(stderr, "error: unable to mmap framebuffer\n");
        exit(1);
    }
}
void closeFBDEV(void)
{
    munmap(FrameBuffer, FixedInfo.smem_len);
    close(FrameBufferFD);
}
int main()
{
    openFBDEV();
    fprintf(stderr, "openFBDEV finish\n");
    memset(FrameBuffer, 128, FixedInfo.smem_len);
    sleep(5);
    closeFBDEV();
    fprintf(stderr, "closeFBDEV finish\n");
    return 0;
}