Processing 1.0 - Processing Discourse - trail....trai....tra...tr...t...

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Index › Programming Questions & Help › OpenGL and 3D Libraries › trail....trai....tra...tr...t...

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trail....trai....tra...tr...t... (Read 2231 times)

bruzz

trail....trai....tra...tr...t...
Jul 27^th, 2009, 10:57am

Hi to all, i'm asking to opengl master if is possible to recreate the trail effect in "pure" opengl... in normal processing environment i pretty simple: basicly is to draw a semi-transparent rect instead to redraw the complete scene, i love this effect!!!

example in P2D
void draw()
{
fill(0,0,0,8); //mostly transparent black
rect(0,0,width,height); // slowly fades anythign drawn previously.
image(myimg,xpos,ypos);
//...... other draw stuff
}

but with opengl doesn't work. Maybe is a stupid question but i'd like to use opengl power to speed up my app...

thanks...

Cedric YaBB Moderator Offline Posts: 1838	Re: trail....trai....tra...tr...t... Reply #1 - Jul 27^th, 2009, 12:58pm but with opengl doesn't work. doesnt it ? Code: import processing.opengl.*; void setup(){ size(500,500,OPENGL); background(0); noStroke(); } void draw() { fill(0,0,0,8); rect(0,0,width,height); fill(255); ellipse(mouseX,mouseY,20,20); }
	twitter.com/CedricKiefer

bruzz YaBB Newbies Offline Posts: 4	Re: trail....trai....tra...tr...t... Reply #2 - Jul 28^th, 2009, 3:40am yes..... unfortunally this way to make "trails" works only with "plain" processing.... opengl redraw every frame deleting the ghost effect... the code runs but the effect doesn't

Cedric YaBB Moderator Offline Posts: 1838	Re: trail....trai....tra...tr...t... Reply #3 - Jul 28^th, 2009, 3:54am so when you use this piece of code it doesnt work for you this is how it looks like for me, Click on it, its a video...
	twitter.com/CedricKiefer

ben_hem

Re: trail....trai....tra...tr...t...
Reply #4 - Jul 28^th, 2009, 9:52am

To clarify, using the "OPENGL" mode in Processing is faster than the default 2D, or P3D, but it's not as fast as straight OpenGL. To use that, you need to initialze an openGL object, align the GLUperspective to match Processing, etc.
Here is an example of this:
http://benhem.com/games/GLP5align
And this is what the following code looks like, in action:
http://benhem.com/games/GLfade

Here is the code you need, for reference in case I move those demos:

Quote:

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

GL  gl;
GLU glu;
float aspect, camZ, xx, yy;

void setup(){
  size(400,400,OPENGL);
  aspect=(float)width/(float)height;
  camZ=((height/2.0) / tan(PI*60.0/360.0));
  glu = new GLU();
  gl = ((PGraphicsOpenGL)g).gl;
}

void draw(){
  gl.glMatrixMode(GL.GL_PROJECTION);
  gl.glLoadIdentity();
  glu.gluPerspective(180/3.0, aspect, camZ/10.0, camZ*10.0);
  glu.gluLookAt(0, 0, camZ, 0, 0, 0, 0, 1, 0);

  gl.glColor4f(0,0,0,.02);
  gl.glBegin(GL.GL_TRIANGLE_STRIP);
  gl.glVertex3f(-width/2,-height/2,0);
  gl.glVertex3f(width/2,-height/2,0);
  gl.glVertex3f(-width/2,height/2,0);
  gl.glVertex3f(width/2,height/2,0);
  gl.glEnd();

  xx=mouseX-width/2;
  yy=mouseY-width/2;

  gl.glColor3f(1,1,1);
  gl.glBegin(GL.GL_TRIANGLE_STRIP);
  gl.glVertex3f(xx-20,yy-20,0);
  gl.glVertex3f(xx+20,yy-20,0);
  gl.glVertex3f(xx-20,yy+20,0);
  gl.glVertex3f(xx+20,yy+20,0);
  gl.glEnd();
}

// enjoy -- Ben

bruzz YaBB Newbies Offline Posts: 4	Re: trail....trai....tra...tr...t... Reply #5 - Jul 28^th, 2009, 11:16am @ cedric.... really strange! I have a macbook pro 2,33.... maybe is the videocard??? mmmmh something to check.... @ ben: thank you. the example you provide me is what i want! now i'm going to merge with my code....

jaylfk Senior Member Offline Posts: 253	Re: trail....trai....tra...tr...t... Reply #6 - Jul 28^th, 2009, 12:48pm Bruzz, i also have a Macbook Pro 2.33 with ATI X1600 and get the very same issue like you, but only when using P5 1.x.x. Beta versions are working fine with this code. It might be related to P5 1.x.x OpenGL lib.

bruzz YaBB Newbies Offline Posts: 4	Re: trail....trai....tra...tr...t... Reply #7 - Jul 29^th, 2009, 12:54am So the "ghost" disappear when the beta goes out. I think the best solution is to to the trail effect in "pure java" to avoid this kind of probelms..... now is time code... thank you all.... ciao

JohnG Ex Member	Re: trail....trai....tra...tr...t... Reply #8 - Aug 3^rd, 2009, 2:34pm The "proper" way to do it which works even with clearing the screen each frame is gl.glAccum(...) and related methods, there should be threads on the boards about them if you search.

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