OpenGL Shaders?

Question

I'm writing a game in Java, LJGWL (OpenGL). I'm using a library that handles a lot of messy details for me, but need to find a lot faster way to do this.

Basically I want to set every pixel on the screen to say a random color as fast a possible. The "random colors" is just an Array [][] that gets updated every 2-3 seconds. I've tried drawing rects and using images, both are pretty slow for what I want to do.

I think I want to learn how to write a GPU shader? That is the fastest way to do this? LJGWL exposes OpenGL api to java. Any basic tutorials on how to get started with OpenGL shaders? Or should I dynamically create a texture of some sort and then just throw up the entire texture, would that be faster?

Answer 1

Textures are the fastest way to draw something on screen, draw a texture mapped quad into the screen, it should be fast enough. When you need to reupload the texture data, use glTexSubimage2D to update it.

No need to use shaders.

Answer 2

I've yet to do any work with shaders in OpenGL, but given the same scenario in multiple occasions, I handled it with a texture I threw up across the screen on top, and it worked quite effectively.

Answer 3

I don't know how you are drawing your pixels exactly, but this limit you hit could be because of the amount of data you transfer (inefficiently?). Updating a screen full of pixels every 2-3 seconds shouldn't be hard at all. Although shaders bring you closer to the graphics card, they will never make inefficient methods fast, so...

Why is your code so slow?

1. What code? What code exactly did you try? What texture did you use, render to, ...?
2. Is it slow? How slow? How fast do you expect it to be?
3. How quickly can one get 1920x1080(?) pixels in video ram, what's your hardware, drivers, OS?

I think you need to edit/repost before we can help you solve your problem. Just because it is slow, is no guarantee at all that shaders will even be one bit faster.

Answer 4

If it were the case that you were statically displaying the same image, than using a texture or display list would suffice. But as you want to frequently update it, shaders really are the best option. Shader code executes on the GPU and modifies data in GRAM, so you have no bottle neck transferring from CPU to GPU. The next best thing would probably be a Pixel or Frame Buffer Object. Buffer Objects let you read/write to GRAM via DMA (without having to go through the CPU) so they can be pretty fast.

I haven't written any shaders yet, so I can't recommend any good resources. But SongHo's OpenGL pages are a good place to learn about Buffer Objects. (His examples are in C++ though)