CODEWITHSUNDEEP
c#openglmemorygraphics
mj_
mj_

Reputation: 6447

OpenGL Tiling an Image into Textures and Run Out of Memory

I'm trying to implement a map of the world that the user can scale and pan around in. I'm running into a problem where my program runs out of memory.

Here's my situation:

0) I'm writing my program in C# and OpenGL

1) I downloaded a JPG image off the web that's a detailed image of the world that is 19 megs in size. Each pixel is 24 bits long.

2) I chop this image up into tiles at run time when my program initializes. I feed each tile into OpenGL using glGenTexture, glBindTexture, and glTexImage2d.

3) In my drawing routine, I draw the tiles one by one and try to draw all of them regardless as to whether or not they're on the screen (that's another problem, I know).

For a small image, everything works fine. For large images however, when I decode the JPG into a bitmap so that I can chop it up, my program's memory footprint explodes to over a gigabyte. I know that JPGs are compressed and the .NET JpegBitmapDecoder object is doing its job decompressing a huge image which is probably what gets me into trouble.

My question is, what exactly can one do in this kind of a situation? Since the C# decoding code is the 1st responsible party for blowing up memory, is there an alternate method of creating tiles and feeding them to OpenGL that I should pursue instead (minus bitmaps)?

Upvotes: 1

Views: 435

Answers (2)

Jacob Parker
Jacob Parker

Reputation: 2556

Obviously you should buy more RAM!

You can store textures in a compressed format on the GPU. See this page (also the SC3T/DXT section.) You may also want to swap textures in and out of video memory as needed. Don't keep the uncompressed data around if you don't need it.

Upvotes: 1

vidario
vidario

Reputation: 479

I'd look into decoding the jpg to a bitmap file and using a stream on the bitmap to asynchronously load the relevant tiles data in view (or as much as memory can handle) - similar to e.g. Google Maps on Android.

I also saw this, but can not confirm that "OOM from a Bitmap is very suspect. This class will throw the memory exception for just about anything that goes wrong, including bad parameters etc."

Upvotes: 0

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