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  Drawing IZOLINES of temperature  (Read 1622 times)
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Offline poonury

Junior Newbie





« Posted 2012-10-29 20:19:22 »

Hello everybody!

I stuck with my problem.

PROBLEM:
- very slow algorithm
- no idea how to improve it
- any existing algorithm in Java/ JOGL?

HOW I DO:
I use shader to calculate izolines of temperature and i obtain for example this:

http://imageshack.us/photo/my-images/26/izoline.png

now i must to draw in JOGL black lines on color edges. I read all pixels from GL buffer.

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public BufferedImage toImage(GL gl, int w, int h) 
    {
        gl.glReadBuffer(GL.GL_FRONT); // or GL.GL_BACK

        ByteBuffer glBB = ByteBuffer.allocate(3 * w * h);
        gl.glReadPixels(0, 0, w, h, GL.GL_BGR, GL.GL_BYTE, glBB);

        BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
        int[] bd = ((DataBufferInt) bi.getRaster().getDataBuffer()).getData();
       
        for (int y = 0; y < h; y++) {
            for (int x = 0; x < w; x++) {
                int b = 2 * glBB.get();
                int g = 2 * glBB.get();
                int r = 2 * glBB.get();
                bd[(h - y - 1) * w + x] = (r << 16) | (g << 8) | b | 0xFF000000;
            }
        }

        return bi;
    }


But trying find edge pixel by pixel is soooo long in time. Like this:

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BufferedImage bi = toImage(m_gl, Resources.dCanvasWidth, Resources.dCanvasHeight);
            for(int i=0; i< 20; ++i)
            {
                System.out.println( i );
                for(int i1=0; i1< bi.getData().getHeight()-1; ++i1)
                {
                    int[] buff1;
                    int[] buff2;
                   
                    buff1 = bi.getData().getPixel(i, i1, (int[]) null );
                    buff2 = bi.getData().getPixel(i, i1, (int[]) null );
                   
                    if( !Arrays.equals(buff1, buff2) )
                    {
                        m_gl.glDrawPixels(i, i1,GL.GL_RGB, GL.GL_INT, blackPixel);
                        m_gl.glFlush();
                       
                    }
                   
                }


Can somebody help me solve this problem?
Offline gouessej
« Reply #1 - Posted 2012-10-29 20:29:55 »

Hi

Maybe you can compute iso-contours in the fragment shader too.

Offline poonury

Junior Newbie





« Reply #2 - Posted 2012-10-29 20:39:17 »

I tried but i havent neighbour pixels.

When I calculate it without neigbours but by function calculating my color. I tried obtain izo by 10 degrees it doted or all black, or line is to width.
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Offline theagentd
« Reply #3 - Posted 2012-10-29 20:41:03 »

Do it in two passes and you'll have access to neighboring pixels in the second pass. You can't have each pixel depend on what's being put into neighboring pixels or you'll get a paradox. =S

Myomyomyo.
Offline poonury

Junior Newbie





« Reply #4 - Posted 2012-10-29 20:45:36 »

Hmm i agree with you but how i can write somthing like that?

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gl.glVertexAttrib1f(vs_fTempAtribute, (float) t1.getValueInNode( Resources.mesh.getFace( Resources.mesh.getArea(dAreaCounter).getFaceNr(dFaceCounter) ).m_dwVertex[0]));
gl.glVertex2d(  Resources.mesh.getVertex( Resources.mesh.getFace( Resources.mesh.getArea(dAreaCounter).getFaceNr(dFaceCounter) ).m_dwVertex[0] ).m_position.x,
                Resources.mesh.getVertex( Resources.mesh.getFace( Resources.mesh.getArea(dAreaCounter).getFaceNr(dFaceCounter) ).m_dwVertex[0] ).m_position.y);
gl.glVertexAttrib1f(vs_fTempAtribute, (float) t1.getValueInNode( Resources.mesh.getFace( Resources.mesh.getArea(dAreaCounter).getFaceNr(dFaceCounter) ).m_dwVertex[1]));
gl.glVertex2d(  Resources.mesh.getVertex( Resources.mesh.getFace( Resources.mesh.getArea(dAreaCounter).getFaceNr(dFaceCounter) ).m_dwVertex[1] ).m_position.x,
                Resources.mesh.getVertex( Resources.mesh.getFace( Resources.mesh.getArea(dAreaCounter).getFaceNr(dFaceCounter) ).m_dwVertex[1] ).m_position.y);
gl.glVertexAttrib1f(vs_fTempAtribute, (float) t1.getValueInNode( Resources.mesh.getFace( Resources.mesh.getArea(dAreaCounter).getFaceNr(dFaceCounter) ).m_dwVertex[2]));
gl.glVertex2d(  Resources.mesh.getVertex( Resources.mesh.getFace( Resources.mesh.getArea(dAreaCounter).getFaceNr(dFaceCounter) ).m_dwVertex[2] ).m_position.x,
               Resources.mesh.getVertex( Resources.mesh.getFace( Resources.mesh.getArea(dAreaCounter).getFaceNr(dFaceCounter) ).m_dwVertex[2] ).m_position.y);


First i put in shader a temperature and it calculate color. Where put second step? On this same vertices? I do not imagine that Sad
Offline theagentd
« Reply #5 - Posted 2012-10-29 21:23:45 »

Render what you're currently doing directly to a texture using a framebuffer object (FBO). That way you'll have the data easily accessible later. Then render (using just a single fullscreen quad) this texture to the screen (back buffer) using a different shader that finds your edges or whatever and adds them to the screen. This is called post-processing a rendered image and is pretty much what you're doing on the CPU right now, am I right?

Myomyomyo.
Offline poonury

Junior Newbie





« Reply #6 - Posted 2012-10-29 21:34:43 »

In the code is not as easy as in theory ;( I can't imagine how ... I need to sleep mayby tomorrow will be better.
Offline gouessej
« Reply #7 - Posted 2012-10-29 23:56:42 »

You can use FBObject to implement theagentd's suggestion.

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