pyopengl-users

[PyOpenGL-Users] Depth problem

[Prashant S. <ani...@ya...>]

I am creating a 2D application using pyOpenGL. Here is the init function:

    glEnable(GL_BLEND)
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
    glEnable(GL_TEXTURE_2D)
    glEnable(GL_LINE_SMOOTH)
    glHint(GL_LINE_SMOOTH_HINT, GL_NICEST)
    glClearColor(0.5, 0.5, 0.5, 0.0)                    # This Will Clear The Background Color To Black
    glDepthFunc(GL_LESS)                # The Type Of Depth Test To Do
    glClearDepth(1.0)                    # Enables Clearing Of The Depth Buffer
    glEnable(GL_DEPTH_TEST)                # Enables Depth Testing
    glShadeModel(GL_SMOOTH)                # Enables Smooth Color Shading
    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()                    # Reset The Projection Matrix
    gluOrtho2D(0,640,480,0)       #This is to make (0,0) at Top-Left
    glMatrixMode(GL_MODELVIEW)

    Everything I am drawing with 'z' less the  1.0 is visible. If I am drawing something where 'z' is greater then 1.0 it's not visible. Although I am creating a 2D application but still I need to maintain a depth of my sprites. The sprites are basically a rectangle with some points and text written on it. For this purpose I am thinking to draw every sprite and it's related content between a fix depth, say between 1.0-2.0. Next one will be 2.1-3.0.
This way when I drag the sprite they will properly over lap another one. But some how things are not working here. Badly need some tips or suggestions.


Cheers




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Re: [PyOpenGL-Users] Depth problem

[George P. <gp...@ti...>]

Prashant,

glClearDepth() doesn't do what you think it does.

Prashant Saxena wrote:
> I am creating a 2D application using pyOpenGL. Here is the init function:
>     glClearColor(0.5, 0.5, 0.5, 0.0)

This means, "when you clear the color buffer, make it all gray".

>     glClearDepth(1.0)
> # Enables Clearing Of The Depth  Buffer

No.  This means, "when you clear the depth buffer, make it
all 1.0".

>     Everything I am drawing with 'z' less the  1.0 is visible.

Because its z is less than the z value already in the depth
buffer (1.0).

> If I am 
> drawing something where 'z' is greater then 1.0 it's not visible. 

Because its z is greater than the z value already in the depth
buffer (1.0), so why bother drawing it?

Call glClearDepth() with a more reasonable value (i.e. one
that's greater than the depth you'll be drawing anything at)
and you should be fine.


--George Paci  <gp...@ti...>

   Most software wakes up each day with a fresh case of amnesia.
   Unfortunately, software that doesn't learn from history dooms users
   to repeat it.    --Bret Victor

Re: [PyOpenGL-Users] Depth problem

[Greg E. <gre...@ca...>]

Prashant Saxena wrote:

> Everything I am drawing with 'z' less the  1.0 is visible. If I am 
> drawing something where 'z' is greater then 1.0 it's not visible.

You haven't set the near and far clipping depths, so
they're defaulting to 0.0 and 1.0.

You need to call glOrtho() to set up a projection, e.g.

   glOrtho(0.0, screen_width, 0.0, screen_height, min_depth, max_depth)

where min_depth and max_depth are the range of z
coordinates that you intend to use.

-- 
Greg