Terribly odd display when using shader and glDrawRangeElements on a Powerbook G4

applmak

Unregistered

Post: #1

Mar 14, 2007 — 09:43 PM

Hello.

I have a Powerbook G4 with an ATI Mobility Radeon 9700. I'm writing a demonstration app that works just fine when using the fixed functionality pipeline of OpenGL; however, when I start using the shader, the GLUT window draws some random address in memory, resulting in a very odd display indeed.

I'll include a code excerpt below. You must know, however, that I'm using my own 2D array of data class called MImage. However, it's unit-tested to death, and I'm sure of its functionality. Here's the code:

Code:

//initialization

glGenBuffersARB(1,&vertexID);

//create generic vertex buffer

g = new MImage<float>(levelData[0]->width(),levelData[0]->height(),2);

MImage<float> &genericVertexBuffer = *g;

for (unsigned int j=0;j<genericVertexBuffer.height();j++)

{

    for (unsigned int i=0;i<genericVertexBuffer.width();i++)

    {

        genericVertexBuffer(i,j,0) = i;

        genericVertexBuffer(i,j,1) = j;

    }

}

glBindBufferARB(GL_ARRAY_BUFFER_ARB,vertexID);

glBufferDataARB(GL_ARRAY_BUFFER_ARB,genericVertexBuffer.dataSize(),genericVertex​Buffer.data(),GL_DYNAMIC_DRAW_ARB);

indices = new unsigned short[6*(genericVertexBuffer.width()-1)*(genericVertexBuffer.height()-1)];

unsigned short *indicesPtr = indices;

for (unsigned int j=0;j<genericVertexBuffer.height()-1;j++)

{

    for (unsigned int i=0;i<genericVertexBuffer.width()-1;i++)

    {

        *(indicesPtr++) = i+j*genericVertexBuffer.width();

        *(indicesPtr++) = i+1+j*genericVertexBuffer.width();

        *(indicesPtr++) = i+(j+1)*genericVertexBuffer.width();

        *(indicesPtr++) = i+1+j*genericVertexBuffer.width();

        *(indicesPtr++) = i+(j+1)*genericVertexBuffer.width();

        *(indicesPtr++) = i+1+(j+1)*genericVertexBuffer.width();

    }

}

indexCount = (unsigned int)(indicesPtr-indices);

//drawing code

glEnableClientState(GL_VERTEX_ARRAY);

glBindBufferARB(GL_ARRAY_BUFFER_ARB,vertexID);

glVertexPointer(2,GL_FLOAT,0,NULL);

MImage<float> &data = *g;

for (unsigned int j=0;j<data.height()-1;j++)

{

    glDrawRangeElements(GL_TRIANGLES,j*data.width(),(j+1)*data.width()+data.wid​th()-1,indexCount/(data.height()-1),GL_UNSIGNED_SHORT,indices+6*j*(data.width()-1));

}

The loop around the glDrawRangeElements is to ensure I don't exceed that the appropriate OpenGL limits for my card.

Anyway, this code works fine when using the fixed pipeline. However, when I enable the following shader, the window doesn't draw correctly.

Code:

//vertex shader

void main()

{

    gl_FrontColor = gl_Color;

    gl_Position = ftransform();

}

//fragment shader

void main()

{

    gl_FragColor = gl_Color;

}

What gives?

Matt

OneSadCookie

Luminary

Posts: 5,125
Joined: 2002.04

Post: #2

Mar 14, 2007 — 09:46 PM

Have you tried the shader in isolation, using the GLSLEditorSample that comes with the developer tools? That'll tell you whether it's your setup or the shader itself.

The PowerPC OpenGL drivers haven't been updated since 10.4.3, it seems, so GLSL is likely to be rather buggy.

applmak

Unregistered

Post: #3

Mar 14, 2007 — 10:02 PM

Yep. It's nearly the simplest shader imaginable.

Ack! Buggy drivers! No support! Death....
It seems like something is wrong with the driver. When I use immediate mode, I have no problem. It's only when I use VBOs + glDrawRangeElements + a shader that things start acting up. Very odd.

Thanks for your reply.

OneSadCookie

Luminary

Posts: 5,125
Joined: 2002.04

Post: #4

Mar 15, 2007 — 01:53 AM

As always, file a bug report -- http://bugreport.apple.com/

Also, try ditching the DrawRangeElements for DrawElements... I've heard a few complaints about DrawRangeElements recently.

applmak

Unregistered

Post: #5

Mar 15, 2007 — 06:13 AM

I did try that, but it doesn't fix the problem.

Thanks for the suggestion, though.

Matt

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