OpenGL 3.1-4.1 new and deprecated features

Question

I've been working with OpenGL for about a year now, and have learned a lot of stuff. Unfortunatly the way I learned it was the old pre 3.x way, meaning immediate mode, default shaders, matrix stacks, etc. I more or less have an idea of what has changed from then to now by looking at the OpenGL specs, however I don't totally understand some of the new ways to do things.

From my understanding they got rid of matrix stacks, meaning you have to keep track of your own transformation matrices, which doesn't seem too complicated. They also got rid of immediate mode, meaning you now need to use VBOs or VAOs (never know which one, maybe both..) to send the pixel/normal/texture,etc. information to the shader program. I don't really get the way these objects works, I think you need to put all the info into them, and provide an ofset of some sort to show the separators between pixel,normal and texture coordinates. Could someone briefly explain how this actually works (or send me a link which explains it)? I tried wikipedia and googling it, but found myself still not quite understanding them.

Another point I would like to know more about are shaders, as I've never used them. I'm not going to ask how to code them or anything, just what needs to go in there and what opengl still does for you. More specifically, what would you need to do in the shaders to get a basic rendering program? I know you need to do all the ligthing calculations and use your matrices to calculate the real vertex position. But does opengl still take care of backface culling, line clipping, polygon filling and other lower level issues, or do you have to code them yourslef into the shaders (or don't they even belong in the shaders)?

Answer 1

Since immediate mode is deprecated doing a "hello triangle" application is a bit more involved. There is a good tutorial on modern OpenGL here:

http://arcsynthesis.org/gltut/

You should read it thoroughly. Bear in mind that it doesn't use VAOs so you'll have to read about it somewhere else afterwards. VAOs don't change things much so you won't have to unlearn things from mentioned tutorial to use them.

And about your second question... Your vertex shader will be executed by OpenGL for every vertex. Your job is to calculate final position of the vertex and prepare data (like normals, light data...) to be sent to fragment shader, given the attributes of vertex and other data you send to shader (uniforms - you'll read about it in tutorial). Fragment shader will be executed per fragment and in fragment shader you are calculating the final color of each fragment.

You can see here:

http://www.opengl.org/sdk/docs/man4/

that things like, glPolygonMode and glCullFace are still there.