Planetarion Forums

Structural Integrity · 13 Nov 2002, 09:47

The SDL library I found today on the net is a genric graphics interface for every OS one can think of (Linux, Windows, BEOS, MAC, Solaris and many more).
It is called on some sites as "the interface that DirectX should have been" and thus I'm quite interrested in what one can do with it. So, I've looked over the tutorials a bit trying to comprehend the structure, but I'm missing something: the 3D engine.
DirectX has quite a 3D engine (as I've read here) but no sign of it in the SDL lib.
I have seen that SDL supports OpenGL, which, as I've seen in a glance, DOES support 3D rendering.
Now, I presume SDL uses OpenGL as it's 3D engine, but what I thought was that OpenGL was only supported in Windows. I this true or is there support for it under other OS-es too?

Also, does anyone have experience with SDL or any other generic graphic engines one can recommend?

I have dreamt about being a 3D-game programmer for a long time, but never found the people who actually could help me with it. Is there any place where I could find some tutoring (or any of you who might help me)?

Raging.Retard · 13 Nov 2002, 20:34

Lets clear some myths up here shall we.

SDL is a media (Media, so graphics, sound, input etc) layer. Its not a 3D layer, and has no native support for 3D rendering. What it does have however, is a nice coupling with the OpenGL library.

OpenGL is a 3D library (and imo better than D3D, but im sure people will argue), created by SGI. OpenGL is not tied to Windows (hence it being Open Graphics Library), and runs on many platforms Win32, Linux, Mac, and obvioulsy Irix (SGI's OS).

I am infact using OGL and SDL for a project im on at the moment. SDL is not the only PI media layer, but its probably the onewith the most tutorials for it (which is great for learning).

There are many OpenGL and SDL tutorials out there, GameDev.net and GameTutorials.com are good examples. Google is your friend.

Structural Integrity · 14 Nov 2002, 10:21

k, I got a nice spinning cube now on the screen in a Windows window, but I have a few problems:

1) When I try to run in full-screen I get an error when trying to create a rendering context... running in window-mode works nicely!

2) I've just tried mapping a texture to my cube, but somehow it fails doing that.
It doesn't generate an error, I just get a white cube, without any texture. Have I missed out something? (I hope you can do a guess what's wrong without the code....)

TheShadow · 14 Nov 2002, 10:42

Quote:

Originally posted by Structural Integrity
1) When I try to run in full-screen I get an error when trying to create a rendering context... running in window-mode works nicely!

2) I've just tried mapping a texture to my cube, but somehow it fails doing that.
It doesn't generate an error, I just get a white cube, without any texture. Have I missed out something? (I hope you can do a guess what's wrong without the code....)

Check out the tutorials at http://nehe.gamedev.net. They may be of help

Structural Integrity · 14 Nov 2002, 11:02

gamedev is down.... I've checked yesterday evening and this morning again...

I used NeHe's tutorial....

[edit]
Could it be the computer I use?
I use a P2 with a 4meg videocard
[/edit]

Structural Integrity · 14 Nov 2002, 11:29

OK... i solved the problem

I had a bitmap of 100*100 pixels.... now, I read on the openGL.org forum that a bitmaps height and width had to be a size of a power of 2 (so, 4, 8, 16, 32, 64, 128, etc)
I enlarged the bitmap to 128*128 and TADA!!!!!!

It's still VERY slow tho....

But that's prolly because I have a resource-eating monster of web-based MSN messenger on here....

I got a very warm and fluffy feeling in my tummy now......

djbass · 14 Nov 2002, 13:54

OpenGL and 3D programming in general has always been on my wish I could do it list.

However I'm rather ****ty at maths in general, yet alone working out vectors and things.

I've done some of the tutorials before, but short of displaying spinning cubes and other assorted primitive objects, they never demonstrate a practical example of using those basic skills on a more advanced level.

Actually, if anyone has suggestions for books I could buy on the subject I'd appreciate it.

=[DJ Bass]=

Structural Integrity · 15 Nov 2002, 09:02

Quote:

Originally posted by djbass
OpenGL and 3D programming in general has always been on my wish I could do it list.

However I'm rather ****ty at maths in general, yet alone working out vectors and things.

I've done some of the tutorials before, but short of displaying spinning cubes and other assorted primitive objects, they never demonstrate a practical example of using those basic skills on a more advanced level.

Actually, if anyone has suggestions for books I could buy on the subject I'd appreciate it.

=[DJ Bass]=

I've read on several places that the GLU library has a loads of functions that take care of large portions of the maths. GLU comes with OpenGL.

This site has a great deal of sources that are ready to use in more complex programs and show that maths is not such a big deal in rendering/displaying.
What is a big deal for programmers is the modelling of objects and designing a way to load the 3D objects into the engine. The site (page 5) has a number of examples of how to load Quake2/3 models into your program, that will allow you to design you models with a Q2/3 Editor and then load/render it in your own program.

On these sites you will also find several recommendations for books.

15 Nov 2002, 10:47

GLU is what we used in gfx @ uni last year. Its not bad, especially if you are only developing a small application. It is not as powerful and as extensive as the SDL library (hence RR using that over GLU i assume).

15 Nov 2002, 10:50

heh i just looked at that site and it seems to be very similar to how our labs progressed. Start off drawing 'something', a couple of labs later youre creating the code to look around a 3d world, and the last lab was creating an orrery (time based movement ahoy)

djbass · 15 Nov 2002, 11:36

Of course, game development is not the issue though, I already am great at making game engines etc, but I have not been able to grasp 3D rendering enough to move into that arena yet.

Actually I think SI was closer to the point, the tutorials and things can teach me how to setup a 3D plane and render object to it. What I am having trouble with I suppose is deciding how I wish to handle the object data (create it dynamically on the fly, or use stored 3d objects that I load from one of the many available file formats that exist). I'm quite fussy about copying other people's work, so I am trying to avoid mainstream formats such as the BSP files used in Id's engines, but at the same time it's an existing format with plenty of editors available and seems to be a very practical technology.

what Bigchiefweale described seemed to be the way to go.

Ultimately though I think I'd like to find a few good books on the subject as published books tend to have a degree of detail that just isn't found in most online tutorials etc

=[DJ Bass]=

Structural Integrity · 15 Nov 2002, 12:01

I have problems understanding the GLUlookat function....
It is used in camera objects to look at a certain point. The function is not well described in the examples I have, nor on the sites I have.

The function takes 9 parameters, all 9 float:

3* position (x,y,z)
3* view (x,y,z)
3* up (x,y,z)

After some testing I found out that the "position" is the absolute position of the view, that the "view" is PROBABLY the point you want to look at. But what is the "up" vector for? I have tried altering the parameters but it seems as if it rotates the camera (x,y and z axis)....
But if this is the case it actually makes the view parameters redundant.... no?

OR.... the "position" is the position of the worlds centre, "view" is the position of the viewers eye, relative to the worlds centre, and "up" is the rotiation of the eye...

well?

anyone?

Structural Integrity · 15 Nov 2002, 13:24

ok, so I did some tests, read a vague post on a forum and think that I understand glulookat now:

http://www.geocities.com/structual/b...?glulookat.bmp

15 Nov 2002, 13:55

up is which direction is 'up' suprisingly enough.

For example if its 0,1,0 its saying upwards is directly along the y axis. Ie ina normal 3d world u would consider this to be up. If up was 0,-1,0 the world would be upside down.

Structural Integrity · 15 Nov 2002, 14:23

Aight.... I understand this part now....

BUT.... I have another question....
I've been playing with my spinning box for some time now, and I just tried to make a second spinning box rotating independantly...

I use the glRotatef function to rotate the first box:
glRotatef(rsqr,1.0f,0.4f,0.2f)

//draw the box

I copied the code from the first box and translated the axis system over the x a bit.... then made the second box (identical to the first one)
My conclusion was that the glRotatef translates the ENTIRE axis-system (concluded that because the second box was spinning all over the place), so what I did was rotate the axis-system back after the first box was drawn:

glRotatef(-1*rsqr,1.0f,0.4f,0.2f)
//translate axis system over x-axis
//rotate axis system again

//draw second box....

This basically works fine and created a second box for me spinning next to the other. But is this the proper way to do this?
I mean, when you are building more complex worlds you certainly want to avoid rotating the axis-system all the time (performance issue).
Or is this REALLY THE WAY to do it?

Summary:

Rotate axis system
draw first box
Rotate axis-system back
translate axis system, move a few units over the x-axis
rotate axis system again
draw second box

15 Nov 2002, 14:33

If you have a function drawbody that does the above. ie

translate axis system,
Rotate axis system ,
draw box

In the case of the first box the translation wouldnt occur.

What you do is:

glPushMatrix();
drawBody ();
glPopMatrix();

The push stores what values you are currently at, does whatever you want, then the pop restores these values.

[edit] Tbh you arnt translating or rating the axis system. The transformations are applied to the object that you are about to draw - its just how theyre stored in the matrices that cause the adverse effects on the (insert word ive forgotten here) matrix [/edit]

Structural Integrity · 19 Nov 2002, 13:04

My second problem I've encountered...
I'm making an object-oriented program now, that draws object that are specified in the init. I also included the ability to set colors and textures of planes of the object.

What I have is an object that is colorred yellow, after that another object is drawn with a texture (the texture is a BMP and has a white background).
What happens is that it draws both objects nicely, but for some odd reason it SEEMS as if it does an addition to the colors (the red in the texture becomes orange-ish, the white yellow)
Also appear the white parts of the drawn object as a grey-ish color.

I have the vague idea that I set some transparency property somewhere, but I can't locate it...
Any tips on what the problem could be and how I can get it out?

djbass · 19 Nov 2002, 14:52

I know absolutely nothing about 3d rendering, but to me it sounds possibly like a lighting issue?

=[DJ Bass]=

Gayle29uk · 19 Nov 2002, 15:02

Have you taken reflection into account? i.e. yellow reflecting off one object onto the textured one?

Structural Integrity · 19 Nov 2002, 15:11

Quote:

Originally posted by djbass
I know absolutely nothing about 3d rendering, but to me it sounds possibly like a lighting issue?

=[DJ Bass]=

COULD be it.... I took out the lighting at a later stage so I could work on my OO structure and see the results better.

The current view is like this:
http://www.geocities.com/structual/bla.html?ogl1.jpg

As you see the texture on the outer cubes is mostly yellow, BUT the bmp's that are loaded are DEFINATELY white. The orange "I RAWK" on the cube is pure red in the bitmap. That's why I think there is a color addition done for some odd reason...

How I draw the scene:

INIT:
Load 8 points in the centre object
Make a plane from points 1,2,3,4
Give it the color WHITE (fully WHITE, it appears as grey-ish

)
Make a second plane between points 2,5,6,2
Give it the color YELLOW

RENDER SCENE
call object.draw, this draws the points/planes defined in the init

Next, I have a WHOLE lot of lines of code that draw the textured cubes:

glBindTexture(GL_TEXTURE_2D, texture[0]); // Select Our Texture

//translate the position, rotate

glBegin(GL_QUADS);

//draw a shietload of quads to make up a cube, including texture mapping ,etc etc

glEnd();

//translate the position, rotate

glBegin(GL_QUADS);

//again a shietload of quads for a cube

glEnd();

It's a mistery to me why it acts like this....

Structural Integrity · 19 Nov 2002, 15:15

Quote:

Originally posted by Gayle28uk
Have you taken reflection into account? i.e. yellow reflecting off one object onto the textured one?

No...

But then again, why is the right plane of the centre object grey-ish??? I clearly told it to be white!

Structural Integrity · 19 Nov 2002, 19:59

It was modulation!!!

http://www.opengl.org/discussion_boa...ML/010693.html

It appears that rendered polygons inherit ones colors (WHAT A STUPID THING!!!!) when not explicitly disabled.

Why would anyone want have modulation on by default?

Structural Integrity · 20 Nov 2002, 07:24

Aight, in the hope any of you can help me with this:

I figured out (with a bit of help) how to get around the modulating bit OF THE TEXTURES.
Used: glTexEnvi(GL_TEXTURE_ENV,GL_TEXTURE_ENV_MODE, GL_REPLACE);

But now, the color my drawn quads are even more effected by the texture.

http://www.geocities.com/structual/bla.html?GL2-2.jpg

HELP!!!!

Structural Integrity · 21 Nov 2002, 09:19

Little update:

It appears as if you can enable and disable texturing. If you forget to disable it before drawing an ordinary polygon it inherits the "average" color of the last drawn texture...

/me goes further with writing his model-loader and normal calculation

Raging.Retard · 22 Nov 2002, 23:58

Just thought id post some of my OpenGL work as ive gotta do a presentation on it on Tuesday.

http://130.88.177.37/phwoar.jpg

Some random scene, but being renderd with my code.

Structural Integrity · 9 Dec 2002, 16:20

Quote:

Originally posted by Raging.Retard
Just thought id post some of my OpenGL work as ive gotta do a presentation on it on Tuesday.

http://130.88.177.37/phwoar.jpg

Some random scene, but being renderd with my code.

looks nice! I guess the textures are from Unreal Tournament (seem to remember the wall/rusty one

)

How big is that room BTW? In OpenGL units....

Raging.Retard · 9 Dec 2002, 18:49

The textures were not stolen from any games, they came from an online pack made by some guy called Evil (sadly I dont have the URL here to credit him).

And in OGL units ive no idea, I made the world in an editor and kept scalling it until it looked right.

MT · 10 Dec 2002, 12:48

Quote:

Originally posted by Raging.Retard
The textures were not stolen from any games, they came from an online pack made by some guy called Evil (sadly I dont have the URL here to credit him).

And in OGL units ive no idea, I made the world in an editor and kept scalling it until it looked right.

All it needs now are some tanks!

Raging.Retard · 10 Dec 2002, 20:12

Im working on it