Re: Texture colour wrapping

Thanks a lot for the example. It helps me quite a bit however I am not sure
how to do what I wish to do. I attached to this email an example of what i
would like to do.
On the left hand side is my original phase map data on a polar grid. I want
to make a polar to cartesian transformation of this phase map so it looks
like the middle plot in the figure attached, here the phase map is on a
cartesian grid. For this two first figures the grayscale cover -5 to 25
radians. Finally I want to wrap the phase data so the maximum grayscale
value is max 6.28 radians.

I managed to do the first step (polar to cartesian) using quad strip and
texture mapping but i am not sure how I can get the vertex value from the
middle stage map as it is already a texture. I am certainly missing
something but I can not see what.



On 6 November 2011 05:23, Dirk Reiners <[email protected]> wrote:

>
>        Hi Brice,
>
>
> On 11/05/2011 03:37 PM, Brice Thurin wrote:
>
>> Hi Dirk,
>>
>> Thanks for your help. So if I understand properly, I first do the
>> geometrical
>> mapping to do the polar to cartesian transformation. Then I do the color
>> mapping?
>>
>
> Yes and no. The actual mapping to color is done by the texture, you just
> need to feed your data into it in a way that puts the wraparound point at 0
> and 1.
>
> I appended a simple example.
>
>
>  That's sound pretty neat to me.
>>
>
> It is! :) Its really cool, as you can mess with texture to show specific
> important values or ranges, make it smooth or stepped (like in my example)
> and many other cool tricks.
>
> Hope it helps
>
>        Dirk
>
>
> #!/usr/bin/python2.4
> #
> # Use texture for visualizating a data value.
> #
> # Based on texturedQuad.py by "Peter Roesch" <[email protected]>
> #
> # This code is licensed under the PyOpenGL License.
> # Details are given in the file license.txt included in this distribution.
>
> import sys
> import array
> import math
>
> try:
>  from OpenGL.GLUT import *
>  from OpenGL.GL import *
>  from OpenGL.GLU import *
> except:
>  print ''' Error PyOpenGL not installed properly !!'''
>  sys.exit(  )
>
> def display(  ):
>        """Glut display function."""
>        glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT )
>        glColor3f( 1, 1, 1 )
>
>        # Draw a regular grid
>        gridres=40
>        for y in [y * 1. / gridres - 0.5 for y in range(0, gridres)]:
>            glBegin(GL_QUAD_STRIP)
>
>            for x in [x * 1. / gridres - 0.5 for x in range(0, gridres +
> 1)]:
>
>                # This is where the data value goes...
>                glTexCoord1f( math.sin(x*x + y*y) * 5  )
>                glVertex3f( x, y, 0 )
>
>                y1 = y + 1. / gridres
>                glTexCoord1f( math.sin(x*x + y1*y1) * 5 )
>                glVertex3f( x, y1, 0 )
>            glEnd(  )
>
>        glutSwapBuffers (  )
>
> def init(  ):
>        """Glut init function."""
>
>        glClearColor ( 0, 0, 0, 0 )
>        glShadeModel( GL_SMOOTH )
>
>        # Build texture. Just a trivial grey step one for now
>        # For a real app you would create a nice lookup table
>        nsteps = 8
>
>        ns = 256/nsteps
>        tmpList = [ int(i/ns)*ns for i in range(0, 256) ]
>        texdata = array.array( 'B', tmpList ).tostring( )
>        texwidth = 256
>
>        glTexParameterf( GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_REPEAT )
>        glTexParameterf( GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_LINEAR )
>        glTexParameterf( GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR )
>
>        glTexImage1D( GL_TEXTURE_1D, 0, 3, texwidth, 0,
>                      GL_LUMINANCE, GL_UNSIGNED_BYTE, texdata)
>        glEnable( GL_TEXTURE_1D )
>
> glutInit( sys.argv )
> glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGB )
> glutInitWindowSize( 250, 250 )
> glutInitWindowPosition( 100, 100 )
> glutCreateWindow( sys.argv[0] )
> init(  )
> glutDisplayFunc( display )
> glutMainLoop(  )
>

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