WorldViz User Forum - Vertex shader performance problem

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Vertex shader performance problem

Hello,

I have just started experimenting with vertex shaders and I have a performance problem. Below is an example program that shows my problem:

Code:

import viz

import vizshape



viz.go()

vizshape.addGrid()

viz.MainView.setPosition(0, 1, -5)



vert = """

uniform float elapsedTime;



void main() {  

  if( gl_MultiTexCoord0.y > 0.0) {

    gl_Vertex.x += sin(gl_Vertex.x * 0.2 + elapsedTime * 1.0) * gl_MultiTexCoord0.y * 0.2;

    gl_Vertex.z += sin(gl_Vertex.y * 0.2 + elapsedTime * 1.0) * gl_MultiTexCoord0.y * 0.2;    

  }

  

  gl_FrontColor = gl_Color;

  gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;

}

"""



shape = vizshape.addQuad()

elapsedTime = viz.addUniformFloat('elapsedTime', viz.tick())

shader = viz.addShader(vert = vert, uniforms = [elapsedTime])

shape.apply(shader)



def onUpdate(e):

        elapsedTime.set(viz.tick())



viz.callback(viz.UPDATE_EVENT,onUpdate)

My problem is that when you check the statistics the Draw time is 15.00 (On my system), while it should be something like 0.02. If I do not update the elapsedTime uniform every frame, the performance is fine (but I have no animation). What am I doing wrong?

Greetings, Joran.

I don't think you are doing anything wrong. I tried your sample code and my draw time is 0.04 using a GeForce 8800 GTS. This might be an issue with your OpenGL drivers.

FYI, you don't have to create your own elapsed time uniform. OpenSceneGraph supplies the following global uniforms that you can use in any shader:

Code:

int osg_FrameNumber;

float osg_FrameTime;

float osg_DeltaFrameTime;

So you can modify your example to use this global uniform instead:

Code:

import viz

import vizshape



viz.go()

vizshape.addGrid()

viz.MainView.setPosition(0, 1, -5)



vert = """

uniform float osg_FrameTime;



void main() {  

  if( gl_MultiTexCoord0.y > 0.0) {

    gl_Vertex.x += sin(gl_Vertex.x * 0.2 + osg_FrameTime * 1.0) * gl_MultiTexCoord0.y * 0.2;

    gl_Vertex.z += sin(gl_Vertex.y * 0.2 + osg_FrameTime * 1.0) * gl_MultiTexCoord0.y * 0.2;    

  }

  

  gl_FrontColor = gl_Color;

  gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;

}

"""



shape = vizshape.addQuad()

shader = viz.addShader(vert = vert)

shape.apply(shader)

I updated my driver and now it works as expected. And I now also use the osg global uniforms. Thanx.

Greetings, Joran.