Processing 1.0 - Processing Discourse - OPENGL code (flickering error)

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Index › Programming Questions & Help › OpenGL and 3D Libraries › OPENGL code (flickering error)

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OPENGL code (flickering error) (Read 2466 times)

ssdesign

OPENGL code (flickering error)
Jan 22^nd, 2009, 10:00am

Hi,
I have been mostly using P3D.
Today I decided to run one of my P3D sketch in OPENGL mode.

When I did that, the code flickers a lot and junk showed on my screen.

So I downloaded a OPENGL sketch from Processing website and it worked perfectly fine.

So I modified my sketch to use beginShape() and endShape() instead of line() and point()

Still the code flickers and shown junk.

Any idea what I am doing wrong?

Here's my code:

Quote:

import processing.opengl.*;

//
float len = random(220);
float radius1 = random(20, 130);
float radius2 = random(10, 100);
float position = random(101);
float num = random(5, 10);
float prevX = 0.0;
float prevY = 0.0;
float x = 0.0;
float y = 0.0;
//
PVector point1, point2;
//
float step = 1 * PI / 180.0;
float theta = 0;
int i=0;
float count = 0;

//
void setup(){
  size(500, 500, OPENGL);
  background(255);
  stroke(0, 20);
}

void draw(){
    count+=1;
    translate(width/2, height/2);
      prevX = x;
      prevY = y;
      x = len * cos(theta) - position * cos(len * theta / radius2);
      y = len * sin(theta) - position * sin(len * theta / radius2);
      //
      point1 = new PVector(prevX, prevY);
      point2 = new PVector(x, y);
      //
      theta += step;
      i++;
      if(prevX!=0){
        stroke(0);
        strokeWeight(1);
       PVector perp = new PVector(point2.y - point1.y, point1.x - point2.x);
       // Length 1
        perp.normalize();
        // Length to n pixels
        perp.mult(60); // Put 10 for 10 pixels
        // Move to point1
        perp.add(point1);
        // Draw it
        stroke(#AA2244);
        strokeWeight(1);
        beginShape(LINES);
        vertex(point1.x, point1.y);
        vertex(perp.x+random(-5, +5), perp.y+random(-5, +5));
        endShape();
      }
}
void mousePressed(){
  background(255);
  initL();
}

void initL(){
  len = random(220);
  radius1 = random(20, 130);
  radius2 = random(10, 100);
  position = random(101);
  num = random(5, 10);
  prevX = 0;
  prevY = 0;
  x = 0;
  y = 0;
}

:: form follows function ::&&http://www.ssdesigninteractive.com/g2

Edvin_Besic

Re: OPENGL code (flickering error)
Reply #1 - Jan 22^nd, 2009, 2:45pm

In your draw( ) loop, you need to clear the background before drawing the
next frame.

void draw( )
{
background( 255 );
... rest of your code ....
}

The junk should dissapear. If by flickering, you mean tearing in the screen,
then you need to enable vertical sync. What that will do is tie your frameRate
with the monitor refresh rate.

This function will do that for you, it's called once (from setup) to enable
vertical sync. If you wish to toggle it you can set the swap interval to 0
at any time to disable it again.

void enableVSync()
{
GL pgl = (PGraphicsOpenGL)g;
gl = pgl.beginGL( );
gl.setSwapInterval( 1 ); // use value 0 to disable v-sync
pgl.endGL( );
}

Hope this helps.

ssdesign YaBB Newbies Offline Posts: 38	Re: OPENGL code (flickering error) Reply #2 - Jan 22^nd, 2009, 5:39pm Hi, Does it mean that you can not do recurcive drawings using OPENGL?
	:: form follows function ::&&http://www.ssdesigninteractive.com/g2

Edvin_Besic YaBB Newbies Offline Posts: 4	Re: OPENGL code (flickering error) Reply #3 - Jan 23^rd, 2009, 9:58am No ofcourse not, if you want to draw over the previous screen simply do not clear it. But then, that junk you were talking about must be something else. Can you post a screenshot?

starkes

Re: OPENGL code (flickering error)
Reply #4 - Feb 9^th, 2009, 8:39am

The worst flickering problems I get are because vsync isn't enabled by default. Maybe that' s your problem? Your code worked perfectly fine for me though.

Anyways I found an example that enables vsync, and it solved all my problems in life. Just copy in the code you need from this:

import processing.opengl.*;
import javax.media.opengl.GL;

PGraphicsOpenGL pgl;
GL gl;

void setup()
{
size(400,400, OPENGL);
pgl = (PGraphicsOpenGL) g; //processing graphics object
gl = pgl.beginGL(); //begin opengl
gl.setSwapInterval(1); //set vertical sync on
pgl.endGL(); //end opengl
}

taifunbrowser

Re: OPENGL code (flickering error)
Reply #5 - Jul 2^nd, 2009, 8:47pm

Not to bring back a topic that's been discussed to death, but I found today that enabling/disabling the Aero theme in Vista can fix the flickering / tearing in opengl applets.

Tried the above code (setSwapInterval with 0 and 1) in Vista Basic:
Both had tearing, no matter the framrate (fast or slow)

Tried with setSwapInterval 0 or 1 in Aero
Neither tore, even up to 120 fps!

Hmm... Must be my weird graphics drivers.

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