Making a Graphics Engine

[Noodles]

So Hi,

I am having some problems finding anything about this matter in the Internet.
I want to write a Graphics Engine, preety straight forward.
I want to make it possible to make moving Objects for example a human(actually there will only be chibi).
So, I got two problems:

-about moving Objects, I was thinking of making an abstract skeleton like stickfigure, which represents the basic movement of, in this example, the chibi.
Then building the mesh around each segment for example the upperleg, and pin the mesh to the abstract stick, so when i move the stick the mesh moves accordingly, but
if im thinking of using knees, how should i best animate these, should i use clipping, so just simply let two meshes clip each other, or should i make extra dynamic meshes for them?
Also how would i realize this structure in lwjgl, im quite new to moving objects in opengl.

-about savig these animation in NOT code segments, i thought about cutting the animation into (maybe 100) pieces and in each piece i can move the "sticks" as far as i like, for easier use maybe even just code 
something in a simmilar manner to : ";wait 10 segments;turn 90° in 30 segments; wait 3 segments; turn -90° in 30 segments;finallize segments"(finallize would be for reaching 100 segments).
Might this design be viable?

I would like to see sample code segments, since that will probably help me alot in understanding how to do this.

Thankyou very much in advance
Noodles

[quew8]

For animating characters in 3d, I think skeletal animation is the way you want to go.  Essentially you transform the skeleton and then each vertex of the mesh has a weighting to each adjacent node on the skeleton and you work out the position based on these weightings. It is quick and if done well looks natural.

However, this is not a simple technique and would require at the very least a strong knowledge of shaders and matrix transformations. It is not for the lighthearted. I would advise looking at something simpler first.

[Noodles]

I have actually worked with opengl once before,
but in that case someone else had set everthing up and only transformations were left to do I actually wrote a shader for that programm so no worries i have donne that before,
my problem is not knowing how to do it, but how to do it best, its supposed to be a high performance game engine.
Im not sure how to use the weightings you suggested ?
Do you know some Web-Page, where I can read about it ? I am not able to find anything on this Topic.

Thanks for the reply though.

[quew8]

If you've done complex transforms before then that's actually a very good place to start from. You will need to read up on vbos though as they are extremely important for performance. http://www.lwjgl.org/wiki/index.php?title=Main_Page (Read either the OpenGL 3.2+ section or "Using FBOs" in the legacy OpenGL section)

http://en.wikipedia.org/wiki/Skeletal_animation

Essentially pass the skeleton, stored as a series of transformation matrices, in a uniform variable (if you are going for performance then you should do this in a texture). Your skin mesh should be stored in a vbo. The real magic happens in the shader (as per usual)

Can't really help you anymore - I've never implemented this myself. (I'll get round to it eventually)

[Noodles]

Ok,

I have another question, I am not sure if I read it correctly but is VBO used server-sided and sends the data to the client and is supposed to do so in real time ? Or was it an exmaple on how VBO is considered to work(with a server-client architecture?).
Well how ever, The Colours, that are used in the Examples on the Wiki, or they supposed to be for Shader purposes ? , since im not sure why I would want to change the location of colour(in form of .gif or .jpeg) that i wrap around the Object, or does this have to be done symmetrical to the conversions ?

[quew8]

A VBO is a vertex buffer object. It is an area in the video card's memory where you can store vertex data so it is at the video card's "fingertips." (Ie. no lengthy copying ops between cpu and gpu). Once the VBO is created and the vertex data stored, you can draw the subject with just two or three OpenGL calls.

http://www.lwjgl.org/wiki/index.php?title=Using_Vertex_Buffer_Objects_(VBO)

Definitely have a read.

[Noodles]

Hi again,

I am starting to try out all of the VBO stuff and i ran into a Problem.
When using VBOs scaling, rotating and translating has to be implemented different, in the example on the Wiki "The Quad with Projection, View and Model matrices"
he sets uniform variables, but these seem to be Global, so my question is:

If i got two Objects that move seperatly, do I have to save both object-Meshes in different VBO's ?
If I wouldnt I would allways move both of the Objects at the same time, the same amount!

Or is there another way to scale rotate and translate.

Ty for any answers.

[quew8]

Problem with a capital 'P.'

You can draw different sections of the vbo with the offset parameter of glDrawElements(). So draw one object, then set the new transformation, then draw the next object.

[Noodles]

Sorry for the "Problem", am German,
So I still got a Problem with understanding this offset, if I say glDrawElements then all Elements get drawn from the offset forward am i right ?
If so then first i draw elements (0 to n) and with offset i draw objects (offset to n), if you ignore interleaving.
Or how do i set how many vertices get drawn for example vertice 0 to 5 then 5 to 10 then 10 to 15 etc ?

[quew8]

That can be changed with the count parameter. So drawing n indices from the m th index can be achieved by:

glDrawElements(GL_WHATEVER, n, GL_UNSIGNED_INT, m * 4);

4 being the size of one integer (unsigned or otherwise)

A tip for later, whenever you are unsure about something like this, I find it helps greatly to take a look at the documentation for the function: http://www.opengl.org/sdk/docs/man2/. That's the docs for OpenGL 2.x

[Noodles]

Well Thank you i guess I was mixing up some functions,
I thought the second param was used for interleaving,
but ok that way of course its easy to do what I want to,

Well Thanks alot.

[quew8]

No problem - that's what the docs are there for.

[Noodles]

Well,
Hi again,

I am at the point of creating Objects for animating of characters,
now then I am running into problems again,
I am thinking about using smooth skinning algorythms for rendering purposes,
So every Vertex will need specific 4 matrices that are deffind by joint transformations,
these joint transformations change almost each rendering cycle, so what is the fastest way to provide these matrices ?
I believe i will have to save them interleaved beside position color and texture data.
Are my assumptions correct? If so is the fastest way there buffersubdata() ?
Or am I missing something ?

Thanks for any help.

[quew8]

Pretty much. Just make sure you create the VBO with the GL_DYNAMIC_DRAW flag (The usage parameter of glBufferData). That informs the video card that you are going to be doing lots of updating and drawing with this VBO. Also, make sure you reuse Buffers as much as possible.

You could also look into using glMapBuffer / glUnMapBuffer but, for what it's worth, my money is on glBufferSubData.

[Noodles]

In this Tutorial
http://graphics.ucsd.edu/courses/cse169_w05/3-Skin.htm

it is suggested to put all the joint matrices in some sort of dynamic accesible array and
only save the index of the matrices psoition interleaved with the position color and textures.
Is this realizable is there some sort of array that I can acces via Shader programm?
For Examble a Uniform Matrix4f array?
I would only have to load this in once since every Vertex uses the same matrix with different weight?

I havent worked too much with Shaders, so im not sure if this is possible or if this is actaully efficient.