pyopengl-users

[PyOpenGL-Users] DrawArrays for a bunch of (unconnected) lines

[Philippe S. <ph...@ph...>]

Hello,

I'm playing with opengl for a tiny chart ploting application,
and facing the following problem:

the line representing the data is displayed, but I cannot
get the horizontal and vertical grid to be displayed.

initialization:

        pygame.init()
        self.surface = pygame.display.set_mode((self.width, self.height), OPENGL|DOUBLEBUF)
        glClearColor(0.0, 0.0, 0.0, 0.0)
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
        glOrtho(0, 1, 0, 1, 0, 1)
        glEnableClientState(GL_VERTEX_ARRAY)
        glDisable(GL_LIGHTING)

data drawing loop:

        glColor(0.8, 0.8, 0.8, 0.0)
        glVertexPointerd(self.gridH)
        glDrawArrays(GL_LINES, 1, len(self.gridH))
        glVertexPointer(4, GL_DOUBLE, 0, self.gridV)
        glDrawArrays(GL_LINES, 1, len(self.gridV))
        glColor(0.65, 1.0, 1.0, 0.0)
        #glVertexPointer(2, GL_DOUBLE, 0, self.points)
        glVertexPointerd(self.points)
        glDrawArrays(GL_LINE_STRIP, 1, self.N/2)
        pygame.display.flip()

self.gridH and gridV are list of 4 elements tuple [(xa0, ya0, xa1, ya1), ...]
self.points is a simple list.

Also, if I replace glVertexPointerd(self.points) with the line just above it,
nothing is displayed.

I'm a newbie, someone can probably help me!

thanks.

Re: [PyOpenGL-Users] DrawArrays for a bunch of (unconnected) lines

[Mike C. F. <mcf...@ro...>]

This would be much easier to debug with example code I could run. 
However, it looks as though the second problem may be related to using a 
list instead of a string or array with the glVertexPointer variant. That 
should probably either work or raise a TypeError rather than silently 
failing.

That doesn't explain the problems with the grid, but that looks more 
like a data issue. You should be aware that you're defining points in 4 
dimensions, not 2. That is, the points are x1,y1,z1,w1 as you are 
passing the parameters into glVertexPointer, not x1,y1,x2,y2, if you've 
defined them as though they were pairs of 2-coordinate points then the 
result will likely be dots rather than lines that are way off in the 
middle of nowhere.

Feel free to forward a running example to me. I'll try to get to looking 
at it sometime this week.

Good luck,
Mike

Philippe Strauss wrote:

>Hello,
>
>I'm playing with opengl for a tiny chart ploting application,
>and facing the following problem:
>
>the line representing the data is displayed, but I cannot
>get the horizontal and vertical grid to be displayed.
>  
>
...

>        glColor(0.8, 0.8, 0.8, 0.0)
>        glVertexPointerd(self.gridH)
>        glDrawArrays(GL_LINES, 1, len(self.gridH))
>        glVertexPointer(4, GL_DOUBLE, 0, self.gridV)
>  
>
You probably meant 2, not 4, here

>        glDrawArrays(GL_LINES, 1, len(self.gridV))
>        glColor(0.65, 1.0, 1.0, 0.0)
>        #glVertexPointer(2, GL_DOUBLE, 0, self.points)
>        glVertexPointerd(self.points)
>        glDrawArrays(GL_LINE_STRIP, 1, self.N/2)
>        pygame.display.flip()
>
>self.gridH and gridV are list of 4 elements tuple [(xa0, ya0, xa1, ya1), ...]
>self.points is a simple list.
>
>Also, if I replace glVertexPointerd(self.points) with the line just above it,
>nothing is displayed.
>
>I'm a newbie, someone can probably help me!
>
>thanks.
>  
>
________________________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://www.vrplumber.com
  http://blog.vrplumber.com