[SDL] Displaying data array

[Scott Harper]

I don't do much with pure SDL (mostly I use it to get cross-platform  
input and context for OpenGL), but depending on how the memory is  
stored for SDL_Image structures, you might be able to just do a  
memcpy() from your array to each R, G, and B channel, assuming that  
you want a grayscale image.  This assumes that the pixel data in  
SDL_Images are arranged with all the similarly colored data together,  
and I just don't know that.  It's entirely possible that they aren't,  
which scraps this paragraph.

More realistically, though, how often do you update the data in the  
array?  If not that often (or at all) you could likely very easily  
just create a new image, copy the data (pixel-by-pixel) to the image,  
and then just blit the image as you normally would.

Lastly, if you do need to update, say, every frame, how bad is it  
ACTUALLY to just iterate through the array and write pixels to  
offscreen memory (an image structure) and then draw the image as  
normal?  I bet if you tried it you may be surprised.  If it's just a  
loop that does some memory copies to an incrementing position in the  
image structure, you may find yourself surprised by just how fast 1+  
GHz actually is.  ~_^

And lastly, if you have already tried it and it IS actually too slow,  
feel free to completely ignore the previous paragraph.  =D

-- Scott

On Mar 21, 2008, at 10:25 AM, Ed Keith wrote:
> I have an array of data in memory that I want to
> display as an image. I can think of two ways of doing
> this, but do not like either one.
>
> I could write the array to the screen pixel by pixel.
> I suspect this will be very slow.
>
> I could write the data to a bit map file and read the
> file into the display. I do not like all this
> unnecessary disk access.
>
> Can anyone suggest a better way?
>
> thank you,
>
>   -EdK
>
> Ed Keith
> e_d_k at yahoo.com
>
> Blog: edkeith.blogspot.com