how to stop linux framebuffer to clear automatically while drawing multiple frames - c

Question

I am writing a gif decoder, This image is an animated image.When I write the first frame, it displays fine. When, I display the second frame, it displays only the changed pixels. Other pixels are automatically changed to black. I don't know why?.
My first frame has the complete picture.
The second frame has again only the pixel changed and it contains the rest of the unchanged pixels.
Now, when I draw the second buffer, it redraws the unchanged pixels also. And the unchanged pixels are drawn as black ( or precisely in monitor I see these unchanged pixels are absent). That's when it has to draw the second frame.It draws the changed pixels( which is correct), but it re-draws the unchanged pixel as well. And this unchanged pixel are seen as a black ( that is no color). I feel it is a refreshing issue. Or It could be something else. Help is appreciated.
Required: It should redraw the complete image.
In short, this is the snippet of my function.
Unfortunately, it clears off the previous display - linux framebuffer.
I want to stop clearning the linux framebuffer.
here is the complete file.
/** This is using the Direct Fb calls here; and is tightly coupled with Linux Framebuffer **/
static int fbfd = 0;
static struct fb_var_screeninfo vinfo;
static struct fb_fix_screeninfo finfo;
static long int screensize = 0;
static char *fbp = 0;
static int x = 0, y = 0;
static long int location = 0;
/** This is a clone to linux Frame buffer, and will be called to dump on Framebuffer **/
char *local_display_mem;
/** local functions **/
static void SetBackground(FrameData *tempInfo);
static void SetPixel(char *fbp, unsigned int x, unsigned int y, Byte red, Byte green, Byte blue);
/** This is the entry function to initialize the display **/
void display_init()
{
// Open the file for reading and writing
fbfd = open("/dev/fb0", O_RDWR);
if (fbfd == -1)
{
perror("cannot open framebuffer device");
exit(1);
}
#ifdef DEBUG
printf("The framebuffer device was opened successfully.\n");
#endif
/** Read the Screen Information **/
if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1)
{
perror("Driver error-- reading fixed information");
exit(1);
}
// Get variable screen information
if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1)
{
perror("Error reading variable information");
exit(1);
}
#ifdef DEBUG
printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel);
#endif
// 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);
local_display_mem = (char*)malloc(screensize);
if ((int)fbp == -1)
{
perror("Error: mmap failed\r\n");
exit(1);
}
#ifdef DEBUG
printf("The framebuffer device was mapped to memory successfully.\n");
#endif
printf("Shreyas..Display Initialized..\r\n");
//munmap(fbp, screensize);
//close(fbfd);
}
/** This function is called by gif_read to display the Image **/
void Display(FrameData *FrameInfo)
{
short int ImageStartX = 0;
short int ImageStartY = 0;
int Index = 0;
printf("\r\n INFO: Display Called.\r\n");
while(1)
{
Index = 0;
ImageStartX = (FrameInfo->frameScreenInfo.LeftPosition);
ImageStartY = (FrameInfo->frameScreenInfo.TopPosition);
while(ImageStartY < ((FrameInfo->frameScreenInfo.ImageHeight)+(FrameInfo->frameScreenInfo.TopPosition)))
{
while(ImageStartX < ((FrameInfo->frameScreenInfo.ImageWidth)+(FrameInfo->frameScreenInfo.LeftPosition)))
{
if(FrameInfo->frame[Index] != FrameInfo->transperencyindex)
{
SetPixel(local_display_mem,ImageStartX,ImageStartY,((FrameInfo->CMAP)+(FrameInfo->frame[Index]))->Red,((FrameInfo->CMAP)+(FrameInfo->frame[Index]))->Green,((FrameInfo->CMAP)+(FrameInfo->frame[Index]))->Blue);
}
Index++;
ImageStartX++;
}
ImageStartY++;
ImageStartX=(FrameInfo->frameScreenInfo.LeftPosition);
}
printf("INFO:..Dumping Framebuffer\r\n");
memcpy(fbp,local_display_mem,screensize);
/** Tune this multiplication to meet the right output on the display **/
usleep((FrameInfo->InterFrameDelay)*100000);
if( FrameInfo->DisposalMethod == 2)
{
printf("set the Background\r\n");
SetBackground(FrameInfo);
}
FrameInfo = FrameInfo->Next;
}
}
static void SetBackground(FrameData *tempInfo)
{
unsigned int ImageStartX=0;
unsigned int ImageStartY=0;
ImageStartX=(tempInfo->frameScreenInfo.LeftPosition);
ImageStartY=(tempInfo->frameScreenInfo.TopPosition);
while(ImageStartY<(tempInfo->frameScreenInfo.ImageHeight))
{
while(ImageStartX<(tempInfo->frameScreenInfo.ImageWidth))
{
SetPixel(local_display_mem,ImageStartX,ImageStartY,255,255,255);
ImageStartX++;
}
ImageStartX=(tempInfo->frameScreenInfo.LeftPosition);
ImageStartY++;
}
}
static void SetPixel(char *fbp_lc, unsigned int x, unsigned int y, Byte red, Byte green, Byte blue)
{
//printf("Shreyas..set pixel called\r\n");
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
(y+vinfo.yoffset) * finfo.line_length;
if (vinfo.bits_per_pixel == 32)
{
*(fbp_lc + location) = blue; // Some blue
*(fbp_lc + location + 1) = green; // A little green
*(fbp_lc + location + 2) = red; // A lot of red
*(fbp_lc + location + 3) = 0; // No transparency
//location += 4;
}
else
{ //assume 16bpp
unsigned short int t = red<<11 | green << 5 | blue;
*((unsigned short int*)(fbp_lc + location)) = t;
}
//printf("Shreyas..set pixel exit called\r\n");
}
/** This is windows version of display function, and it works correctly.
void Display(FrameData *FrameInfo)
{
short int ImageStartX=0;
short int ImageStartY=0;
int Index=0;
DisplayCntrl=GetDC(hWnd);
printf("Shreyas.. Display Init is called\r\n");
//display_init();
while(1)
{
Index=0;
ImageStartX=(FrameInfo->frameScreenInfo.LeftPosition);
ImageStartY=(FrameInfo->frameScreenInfo.TopPosition);
while(ImageStartY<((FrameInfo->frameScreenInfo.ImageHeight)+(FrameInfo->frameScreenInfo.TopPosition)))
{
while(ImageStartX<((FrameInfo->frameScreenInfo.ImageWidth)+(FrameInfo->frameScreenInfo.LeftPosition)))
{
if(FrameInfo->frame[Index]!=FrameInfo->transperencyindex)
SetPixel(DisplayCntrl,ImageStartX,ImageStartY,RGB(((FrameInfo->CMAP)+(FrameInfo->frame[Index]))->Red,((FrameInfo->CMAP)+(FrameInfo->frame[Index]))->Green,((FrameInfo->CMAP)+(FrameInfo->frame[Index]))->Blue));
Index++;
ImageStartX++;
}
ImageStartY++;
ImageStartX=(FrameInfo->frameScreenInfo.LeftPosition);
}
Sleep((FrameInfo->InterFrameDelay*10));
WaitForSingleObject(hWnd,10);
if( FrameInfo->DisposalMethod==2)
{
SETBACKGROUND(FrameInfo);
}
FrameInfo=FrameInfo->Next;
}
}
This is the windows version of the same code.
extern hWnd;
HDC DisplayCntrl;
void SETBACKGROUND(FrameData *tempInfo)
{
unsigned int ImageStartX=0;
unsigned int ImageStartY=0;
ImageStartX=(tempInfo->frameScreenInfo.LeftPosition);
ImageStartY=(tempInfo->frameScreenInfo.TopPosition);
while(ImageStartY<(tempInfo->frameScreenInfo.ImageHeight))
{
while(ImageStartX<(tempInfo->frameScreenInfo.ImageWidth))
{
SetPixel(DisplayCntrl,ImageStartX,ImageStartY,RGB(255,255,255));
ImageStartX++;
}
ImageStartX=(tempInfo->frameScreenInfo.LeftPosition);
ImageStartY++;
}
}
void Display(FrameData *FrameInfo)
{
short int ImageStartX=0;
short int ImageStartY=0;
int Index=0;
DisplayCntrl=GetDC(hWnd);
printf("the size of short int is %d",sizeof(short int));
while(1)
{
Index=0;
ImageStartX=(FrameInfo->frameScreenInfo.LeftPosition);
ImageStartY=(FrameInfo->frameScreenInfo.TopPosition);
while(ImageStartY<((FrameInfo->frameScreenInfo.ImageHeight)+(FrameInfo->frameScreenInfo.TopPosition)))
{
while(ImageStartX<((FrameInfo->frameScreenInfo.ImageWidth)+(FrameInfo->frameScreenInfo.LeftPosition)))
{
if(FrameInfo->frame[Index]!=FrameInfo->transperencyindex)
{
SetPixel(DisplayCntrl,ImageStartX,ImageStartY,RGB(((FrameInfo->CMAP)+(FrameInfo->frame[Index]))->Red,((FrameInfo->CMAP)+(FrameInfo->frame[Index]))->Green,((FrameInfo->CMAP)+(FrameInfo->frame[Index]))->Blue));
}
Index++;
ImageStartX++;
}
ImageStartY++;
ImageStartX=(FrameInfo->frameScreenInfo.LeftPosition);
}
Sleep((FrameInfo->InterFrameDelay*10));
WaitForSingleObject(hWnd,10);
if( FrameInfo->DisposalMethod==2)
{
SETBACKGROUND(FrameInfo);
}
FrameInfo=FrameInfo->Next;
}
}

Answer 1

Since you use a local memory buffer local_display_mem, it doesn't matter if somebody would clear the framebuffer - the memcpy will overwrite every pixel.
This means that the condition FrameInfo->frame[Index] != FrameInfo->transperencyindex is always true for some reason since that would cause the algorithm to set each pixel again instead of only updating the changed pixels.