how to use loadFromData in painter

[sar_van81]

hi everyone,

i have a RGB values in an character array. can anyone say me to use loadFromData function in QPixmap inorder to convert the RGB datas to a pixmap...?
i did as follows:

void paintEvent(QPaintEvent *)
{
unsigned char buffer[20]={0,0,0,0,0,255,255,255,255,255,0,0,0,0,0};
QPixmap pixmap;
if(pixmap.loadFromData(buffer,20,0,QPixmap::Auto);
QPainter p(this);
p.drawPIxmap(0,0,pixmap,0,0,-1,-1);
}

void paintEvent(QPaintEvent *)
{
unsigned char buffer[20]={0,0,0,0,0,255,255,255,255,255,0,0,0,0,0};
QPixmap pixmap;
if(pixmap.loadFromData(buffer,20,0,QPixmap::Auto);
QPainter p(this);
p.drawPIxmap(0,0,pixmap,0,0,-1,-1);
}

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. the code gets compiled without error. but nothing is coming on the screen.can anyone provide suggestions for this...?
are these steps correct...? if no can any correct me...?

thanks in advance,

saravanan

[wysota]

You need more than just the data:

The loader attempts to read the pixmap using the specified format. If the format is not specified (which is the default), the loader probes the file for a header to guess the file format.

You have to provide a valid header for the format you wish to use.

In your situation it might be better to create an empty QImage and then use setPixel() or bits() to set the data.

[sar_van81]

hi,

i tried with setpixel.but still not got anything. i tried as follows:

QImage img;
if(img.valid(10,10))
img.setPixel(10,10,200);
else printf("\n coordinate not valid..");

like this repeated for about 10 point from x=10,y=0 to x=20,y=0.
but when i compiled and executed the code, there were following errors:

coordinate not valid..
QImage::setPixel: x=10 out of range

.since i'm using depth as 32bit i gave 200 value to index_or_rgb. i gave 0 also.did not work out.

Also i tried the following:
QImage img;
img.setColor(19,qRgb(255,255,0));
*(img.scanLine(20)+20)=19;
.but same error came.

QImage::setColor: Index 19 out of range
QImage::scanLine: Index 20 out of range
Segmentation fault
.

Am i missing something...?Is this corect ...?can you say where am going wrong...?

[sar_van81]

hi...

thank you for the suggestion of setPixel. i got it working.

i did as follows:
QImage image(x,y,32);
image.setAlphaBuffer( true );
for ( uint j = 0; j <x; j++ )
{
for ( uint i = 0; i <y; i++ )
{
QRgb pixel;
pixel = qRgb(0,0,0);
image.setPixel( i, j, pixel );
}
}
. this worked perfectly. earlier i did not create QImage and set the pixel value. now i created QImage and then set the pixel value.

saravanan.

[sar_van81]

hi..

not over yet...i tried specifying the format in loadFromData as "BMP"as follows:

unsigned char buffer[20]={255,255,255,255,255,255,255,255,255,255,255,255, 255,255,255,255,255,255,255,255};
QImage img(100,100,32);
img.setAlphaBuffer( true );

if(img.loadFromData(buffer,20,"BMP"))
printf("\n the image is loaded...\n");
else printf("\n image not loaded...\n");

but image is not loaded.. is this correct...?

any suggestions for this...?

[wysota]

I don't see a valid BMP header here...

http://www.fastgraph.com/help/bmp_header_format.html

[sar_van81]

hi...

thanks for the response.but still a bit clarification.can you say me how to specify the BMP header in this ...?

[wysota]

You can't just pass the pixel data, you need to pass the data in a format of your choice. For example if you want to feed the data in BMP format, the data has to contain the BMP header. Check out the link I gave you, you have to construct a block of data according to the rules mentioned there. If you just want to set some pixels though, I suggest you use QImage::setPixel() instead.

[sar_van81]

hi..

yeah i saw the link . i had programmed like this: i'l open a bmp image, read the file header information and will allocate the temporary buffer with size given in the file header information. then feed this temproray buffer to the QImage::loadFromData ( const uchar * buf, uint len, const char * format = 0 ).

but still could not get it.i had attached the code.

is this correct way....?

[wysota]

If the file is a valid BMP file, then just create the QImage from the file...

QImage imag("/home/qtprograms/test8.bmp");

QImage imag("/home/qtprograms/test8.bmp");

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[sar_van81]

hi....

if we use like this directly then is there any need for loadFromData ... i.e. is this following correct..?

QImage img("/home/qtprograms/text8.bmp");
QPainter p;
p.drawImage ( QPoint(0,0),img,0);

..
sorry for the late reply. went out-of-station.