Full HD 2D Texture Memory OpenGL

Question

I am in the process of writing a full HD capable 2D engine for a company of artists which will hopefully be cross platform and is written in OpenGL and C++.

The main problem i've been having is how to deal with all those HD sprites. The artists have drawn the graphics at 24fps and they are exported as png sequences. I have converted them into DDS (not ideal, because it needs the directx header to load) DXT5 which reduces filesize alot. Some scenes in the game can have 5 or 6 animated sprites at a time, and these can consist of 200+ frames each. Currently I am loading sprites into an array of pointers, but this is taking too long to load, even with compressed textures, and uses quite a bit of memory (approx 500mb for a full scene).

So my question is do you have any ideas or tips on how to handle such high volumes of frames? There are a couple of ideas i've thought've of:

• Use the swf format for storing the frames from Flash
• Implement a 2D skeletal animation system, replacing the png sequences (I have concerns about the joints being visible tho)

How do games like Castle Crashers load so quickly with great HD graphics?

Answer 1

Well the first thing to bear in mind is that not all platforms support DXT5 (mobiles specifically).

Beyond that have you considered using something like zlib to compress the textures? The textures will likely have a fair degree of self similarity which will mean that they will compress down a lot. In this day and age decompression is cheap due to the speed of processors and the time saved getting the data off the disk can be far far more useful than the time lost to decompression.

I'd start there if i were you.

Answer 2

24 fps hand-drawn animations? Have you considered reducing the framerate? Even cinema-quality cel animation is only rarely drawn at the full 24-fps. Even going down to 18 fps will get rid of 25% of your data.

In any case, you didn't specify where your load times were long. Is the load from harddisk to memory the problem, or is it the memory to texture load that's the issue? Are you frequently swapping sets of texture data into the GPU, or do you just build a bunch of textures out of it at load time?

If it's a disk load issue, then your only real choice is to compress the texture data on the disk and decompress it into memory. S3TC-style compression is not that compressed; it's designed to be a useable compression technique for texturing hardware. You can usually make it smaller by using a standard compression library on it, such as zlib, bzip2, or 7z. Of course, this means having to decompress it, but CPUs are getting faster than harddisks, so this is usually a win overall.

If the problem is in texture upload bandwidth, then there aren't very many solutions to that. Well, depending on your hardware of interest. If your hardware of interest supports OpenCL, then you can always transfer compressed data to the GPU, and then use an OpenCL program to decompress it on the fly directly into GPU memory. But requiring OpenCL support will impact the minimum level of hardware you can support.

Don't dismiss 2D skeletal animations so quickly. Games like Odin Sphere are able to achieve better animation of 2D skeletons by having several versions of each of the arm positions. The one that gets drawn is the one that matches up the closest to the part of the body it is attached to. They also use clever art to hide any defects, like flared clothing and so forth.