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Ignifex

OpenGL Frustrum deprecated

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Ignifex    520
Hi, I've been playing around with OpenGL 3.0 a bit since its release, trying to work my way around the deprecated features. I understand that the fixed pipeline was practically deprecated, so everything should be drawn using shaders. One thing I stumbled upon was the deprecated projection and modelview matrices, including the Frustrum and Translate/Rotate calls. What is now the best way to get the view transform matrix (modelview * projection) into the vertex shader? I know how to compute it myself, but having to do so wouldn't be very userfriendly. Regards, Ignifex

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projectileman    122
I guess that they (khronos) did that because they're focusing on what the hardware does rather than support some functions that can be made on the application side.

May it's more efficient making some arithmetic calculations on the CPU than sending commands to GL.

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HuntsMan    368
Use an uniform to upload your matrices to shaders, but that probably will need to track your transformation matrices in the CPU.

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haegarr    7372
All glFrustum, glOrtho, glRotate, glTranslate, ... were likely be computed by the driver on the CPU, and only the results were pushed into the GPU.

Dropping all the predefined uniforms and attributes means to unburden GLSL and the GL API from semantics that are insufficient in some cases anyhow. E.g. what if you have to transport a 3rd color, a 2nd vertex position, or something like that? Such things happen often enough. IMHO it is a a logical step to unify the access down to generic uniforms and attributes. I'm currently implementing a graphics techniques and styles system based on shader scripts, and I would be happy if the current OpenGL would already have dropped the predefined semantics...

glRotate and friends are also mainly superflous. All projects a bit behind test projects have to implement an own co-ordinate frame system anyhow (okay, they need not really, but scan the threads here at GDnet, and you see that it is better to do that kind of stuff yourself instead of relying on OpenGL's matrix stacks). My engine currently consists of roughly 180 classes, and there is no single glTranslate or glRotate inside.

So, IMHO, it is more user friendly than user unfriendly to drop those stuff; it is just senseful to unburden the API from mainly useless stuff. That slims the API and makes it more readable and hence easier to learn. That is also a kind of user friendliness.

Just my 2 cents, of course.

EDIT: And I bet that utility libraries countervailing these "deficits" will occur in masses.

[Edited by - haegarr on August 17, 2008 10:40:40 AM]

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Ignifex    520
I agree that it will be better not to have the predefined uniforms and be able to fully define attributes.
As you said about the utility libraries, I'm mainly looking for the CPU implementation of gluPerspective and gluLookAt, which would return the matrix as a simple array, to be sent to the vertex shader. For now, I'll write my own implementation.

EDIT: Btw, as Carmack said, slimming the API is indeed the way to go.

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Ignifex    520
After a look at the source code of your library, which looks really useful, I see your glhPerspectivef function calls glFrustrum, which is now deprecated. I mean to get a 4x4 matrix in main memory, then use that as a uniform parameter for the vertex shader.

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zedz    291
heres what I have, beaware your matrix order might be different to mine

void MATRIX44::frustum( float l, float r, float b, float t, float n, float f )
{

// 2n r+l
// ---- 0 ----- 0
// r-l r-l

// 2n t+b
// 0 ---- ----- 0
// t-b t-b

// f+n 2fn
// 0 0 - ---- - ----
// f-n f-n

// 0 0 -1 0

a00 = (2.0*n) / (r-l);
a10 = 0.0;
a20 = 0.0;
a30 = 0.0;

a01 = 0.0;
a11 = (2.0*n) / (t-b);
a21 = 0.0;
a31 = 0.0;

a02 = (r+l) / (r-l);
a12 = (t+b) / (t-b);
a22 = -(f+n) / (f-n);
a32 = -1.0;

a03 = 0.0;
a13 = 0.0;
a23 = -(2.0*f*n) / (f-n);
a33 = 0.0;
}


if u check the opengl spec for the Frustum(...) command u can work out whats going on

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V-man    813
Quote:
Original post by Ignifex
After a look at the source code of your library, which looks really useful, I see your glhPerspectivef function calls glFrustrum, which is now deprecated. I mean to get a 4x4 matrix in main memory, then use that as a uniform parameter for the vertex shader.


You should do
float projectionMatrix[16];
glhLoadIdentityf2(projectionMatrix);
glhPerspectivef2(projectionMatrix, fovy, aspect, znear, zfar);

and upload the matrix to your shader.

glhPerspectivef and other functions will be removed in the next version which will appear in a day or 2.

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