Weird video_buffer formula
I came across the following formula...
USHORT *video_buffer;
// pretend that it points to the primary surface..
video_buffer[x + 640*y] = color;
To me, this doesn't make much sense. What I do know though, is that 640 is the number of pixels per row on the screen (right?), and color is a pointer to PALETTEENTRY (right?). What is wracking my brain right now is why you multiply y by how many pixels per row and then add x. Can anyone shoot this into the clear for me? Thanks to all!
Edit: When I point video_buffer to the primary display, I have always been using this..
video_buffer = (USHORT *)ddsd.lpSurface;
Could I, for arguments sake, point the video buffer to the primary surface by doing this:
video_buffer = lpddprimary; // lppddprimary is the primary surface
Thanks!
GO LEAFS GO!
Edited by - Fredric on 5/6/00 8:32:14 PM
The video memory is address linearly, so for each row down you have to add the width of a row. For example, coordinates (47, 4) would mean x=47 and y=4. So the pixel would be at (47 + 640 + 640 + 640 + 640), or (x + width*y).
Also note that you should NOT be using "640" in the equation, but rather ddsd.lPitch because DirectDraw may be using more than 640 bytes per row, even on 8-bit surfaces.
aig
Also note that you should NOT be using "640" in the equation, but rather ddsd.lPitch because DirectDraw may be using more than 640 bytes per row, even on 8-bit surfaces.
aig
Ohhhhhh....... I get it now! So, if say I had the coordinates (23, 3), it would be:
// x=23, y=3
video_buffer(23 + ddsd.lPitch + ddsd.lPitch + ddsd.lPitch);
but in code, it would actually be:
video_buffer(x + ddsl.lPitch*y);
That''s cool, thanks! It''s kind of confusing, but your explanation was really easy to understand! Thanks An Irritable Gent!
GO LEAFS GO!
// x=23, y=3
video_buffer(23 + ddsd.lPitch + ddsd.lPitch + ddsd.lPitch);
but in code, it would actually be:
video_buffer(x + ddsl.lPitch*y);
That''s cool, thanks! It''s kind of confusing, but your explanation was really easy to understand! Thanks An Irritable Gent!
GO LEAFS GO!
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