c0c
Subj : Re: Screen Capture function
To   : borland.public.cpp.borlandcpp
From : Bob Gonder
Date : Sat Jul 03 2004 04:36 pm

Jeff Baker wrote:

>Well it's the strangest thing. The resulting bmp file looks as if it is
>zoomed in and is only displaying every other pixel. Seeing the created file
>makes me think that I'm not padding the data section of the file correctly.
>I am unable to find information telling me if each pixel is represented by a
>byte or an int but in either case the program captures the screen
>identically. This leads me to believe that two or more pixels are contained
>in a single byte/int. So I'll have to tinker with shifting a pixel left and
>adding the next to it then write the byte or int to the file. My other

Yeah, that's what I mentioned...

>> Is this structure aligned (packed) correctly?
>I looked up the structure from the wotsit web site. I've use information
>from them before an I trust it as a good source of information
>(http://www.wotsit.org/search.asp?s=graphics)

Not at all what I was asking. "In Your Program" When It Is Compiled,
Is The Structure Internally Aligned Correctly??  Is file_size Exactly
2 bytes into the structure, or is it 4bytes *When*Compiled*?

>> Is file_size at bmp_file+2?
>I'm not sure what you mean but the file size is suppose to be the complete

Read my fingers.  Is file_size AT (Located At) bmp_file+2?  The third
byte of the structure? With some compiler settings, it will be at the
fith byte, which is wrong.

>file size in bytes. However I've noticed that this is never the case with
>any bitmap I've looked at. The bmp_file is supposed to be the size of the
>bitmap data in bytes but agin, this is never the case.

No, file_size is the size of the BMP in bytes, not the DATA. It is the
File Size, not the Data Size. Hence the name.

>> >bmp.file_size = 22326;
>>
>> Is that the correct file size?
>> 640*480 alone is bigger than that.
>Yes, I found this to be very interesting as well. If I create a 640x480x16
>bmp using M$ Paint the size is always 150K but the bmp.file_size is also
>always 22326. I don't pretend to understand why this is but it is.

Guessing it's because you were displaying it as a short int instead of
the long it is.

>> >bmp.bitmap_size = 22208;
>>
>> Is that the correct size?
>> You are writting 640*480 bytes!
>Yes, the function should capture the entire screen (640x480x16) but as I've
>covered above bmp.bitmap_size does not seem to actually represent the size
>correctly in any BMP I've looked at.

So you just picked a number out of the air? amazing.

>I suspect this is true as well. Do you recommend shifting the pixel data to
>the left twice then add the next? Like this...
>for (x = 0; x <= (bmp.width-1); x+=2)

	NOT equal, definately Not Equal
	; x < (bmp.width-1);

>    {
>    pixel = getpixel(x,y) << 2;

How many bits are you shifting there?
How many bits are you working with?

>    pixel += getpixel(x,y);

And what happens if there's something in the upper 4 bits of GetPixel?

.

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