Writing to framebuffer directly on Android

Question

I've a rooted phone with Android 4.2.2. I'd like to use minui API used (source here) in bootloader code to draw stuff on the screen. minui is much simpler than native OpenGL and I don't need any complex functionality exposed by OpenGL.

The problem is that I can't write stuff directly to fb0 device. FBIOPUT_VSCREENINFO fails for unknown reason.

How can I draw directly to fb0 on Android, or how can I use minui outside the bootloader mode?

Answer 1

Source code,test it works in Qualcomm platform MSM89xx:

panel_test.c

#include <unistd.h>  
#include <stdio.h>  
#include <fcntl.h>  
#include <linux/fb.h>  
#include <sys/mman.h>  
#include <stdlib.h>
#include "yellow_face.zif"
int main()  
{  
    int fbfd = 0;  
    struct fb_var_screeninfo vinfo;  
    struct fb_fix_screeninfo finfo;  
    struct fb_cmap cmapinfo;  
    long int screensize = 0;  
    char *fbp = 0;  
    int x = 0, y = 0;  
    long int location = 0;  
    int b,g,r;  
    // Open the file for reading and writing  
    fbfd = open("/dev/graphics/fb0", O_RDWR,0);                    // 打开Frame Buffer设备  
    if (fbfd < 0) {  
                printf("Error: cannot open framebuffer device.%x\n",fbfd);  
                exit(1);  
    }  
    printf("The framebuffer device was opened successfully.\n");  
  
    // Get fixed screen information  
    if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {            // 获取设备固有信息  
                printf("Error reading fixed information.\n");  
                exit(2);  
    }  
    printf("\ntype:0x%x\n", finfo.type );                            // FrameBuffer 类型,如0为象素  
    printf("visual:%d\n", finfo.visual );                        // 视觉类型：如真彩2，伪彩3   
    printf("line_length:%d\n", finfo.line_length );        // 每行长度  
    printf("\nsmem_start:0x%lx,smem_len:%u\n", finfo.smem_start, finfo.smem_len ); // 映象RAM的参数  
    printf("mmio_start:0x%lx ,mmio_len:%u\n", finfo.mmio_start, finfo.mmio_len );  
      
    // Get variable screen information  
    if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {            // 获取设备可变信息  
                printf("Error reading variable information.\n");  
                exit(3);  
    }  
    printf("%dx%d, %dbpp,xres_virtual=%d,yres_virtual=%dvinfo.xoffset=%d,vinfo.yoffset=%d\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel,vinfo.xres_virtual,vinfo.yres_virtual,vinfo.xoffset,vinfo.yoffset);  

	screensize = finfo.line_length * vinfo.yres_virtual;
    // Map the device to memory 通过mmap系统调用将framebuffer内存映射到用户空间,并返回映射后的起始地址  
    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");  
/***************exampel 1**********************/
	b = 10;
	g = 100;
	r = 100;
    for ( y = 0; y < 340; y++ )
        for ( x = 0; x < 420; x++ ) { 
      
         location = (x+100) * (vinfo.bits_per_pixel/8) + 
             (y+100) * finfo.line_length; 
      
         if ( vinfo.bits_per_pixel == 32 ) {        //          
                        *(fbp + location) = b; // Some blue  
                        *(fbp + location + 1) = g;             // A little green  
                        *(fbp + location + 2) = r;             // A lot of red  
                        *(fbp + location + 3) = 0;     // No transparency  
         }
      
        }
/*****************exampel 1********************/
/*****************exampel 2********************/		
 	unsigned char *pTemp = (unsigned char *)fbp;
	int i, j;
	//起始坐标(x,y),终点坐标(right,bottom)
	x = 400;
	y = 400;
	int right = 700;//vinfo.xres;
	int bottom = 1000;//vinfo.yres;
	
	for(i=y; i< bottom; i++)
	{
		for(j=x; j<right; j++)
		{
			unsigned short data = yellow_face_data[(((i-y)  % 128) * 128) + ((j-x) %128)];
			pTemp[i*finfo.line_length + (j*4) + 2] = (unsigned char)((data & 0xF800) >> 11 << 3);
			pTemp[i*finfo.line_length + (j*4) + 1] = (unsigned char)((data & 0x7E0) >> 5 << 2);
			pTemp[i*finfo.line_length + (j*4) + 0] = (unsigned char)((data & 0x1F) << 3);
		}
	} 
/*****************exampel 2********************/	
//note：vinfo.xoffset =0 vinfo.yoffset =0 否则FBIOPAN_DISPLAY不成功
	if (ioctl(fbfd, FBIOPAN_DISPLAY, &vinfo)) {    
                printf("Error FBIOPAN_DISPLAY information.\n");  
                exit(5);  
    }  
	sleep(10);
	munmap(fbp,finfo.smem_len);//finfo.smem_len == screensize == finfo.line_length * vinfo.yres_virtual 
    close(fbfd);  
    return 0;  
}

Android.mk

# Copyright 2006-2014 The Android Open Source Project

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)

LOCAL_SRC_FILES:= panel_test.c


LOCAL_SHARED_LIBRARIES        := $(common_libs) libqdutils libdl liblog libbase libcutils
LOCAL_C_INCLUDES              := $(common_includes) $(kernel_includes)
LOCAL_ADDITIONAL_DEPENDENCIES := $(common_deps) $(kernel_deps)

LOCAL_MODULE := panel_test

LOCAL_CFLAGS := -Werror

include $(BUILD_EXECUTABLE)

include $(call first-makefiles-under,$(LOCAL_PATH))

yellow_face.zif

yellow_face.zif

Answer 2

device node:/dev/graphics/fb0

you can build in Android tree or use arm-linux-gcc.

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

likes a normal embeded linux, there is a sample:

#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;
}