Re: pBuffer

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Phil Keslin (philk++at++cthulhu.engr.sgi.com)
Tue, 15 Dec 1998 10:33:00 -0800

On an Impact SI with your current framebuffer config (1280x1024) you
only get one 36 bit buffer and a second 32 bit buffer. If you have a
depth buffer, it must reside in the 32 bit buffer. The color buffers can
reside in either. Because of these limits, you can only get one pbuffer
that resides in the 32 bit buffer. That means that you can't also have
depth (the pbuffer and z must both be resident to render and they would
have to share the same physical resource for this to happen).

You can change the timing table to 1024x768_72_pbuf which will give you
an additional 36 bit buffer. This should allow for a pbuffer with depth
and a window with depth. Only one can be current at any one time or you
will get a BadAlloc error from the server (i.e., can't do
glXMakeCurrentReadSGIX with both drawables).

There is a performance penalty for doing this. Since the depth for the
pbuffer and window will use the same physical resource, the depth values
will be swapped as each drawable is made current. This can be expensive.

If you are doing fullscreen rendering, you can switch to the 1024x768_72
timing table and get a double buffered 8 bit visual. You can then use
the back buffer for your temporary, offscreen buffer (unless of course
you are using the pbuffer as a cached storage area).

- Phil

Ruediger Westermann wrote:
>
> Hi Phil,
> here's the graphics configuration
>
> /////////////////////////////////////////////////////////////////////////////
>
> server glx vendor string: SGI
> server glx version string: 1.2 Irix 6.5
> server glx extensions (GLX_):
> EXT_import_context, EXT_visual_info, EXT_visual_rating,
> SGI_make_current_read, SGI_swap_control, SGI_video_sync, SGIX_dm_pbuffer,
> SGIX_fbconfig, SGIX_pbuffer, SGIX_swap_group.
> client glx version 1.1
> client glx extensions (GLX_):
> EXT_import_context, EXT_visual_info, EXT_visual_rating,
> SGI_make_current_read, SGI_swap_control, SGI_video_sync, SGIX_fbconfig,
> SGIX_pbuffer, SGIX_swap_group.
> OpenGL vendor string: SGI
> OpenGL renderer string: IMPACT/1/1/0
> OpenGL version string: 1.1 Irix 6.5
> OpenGL extensions (GL_):
> EXT_abgr, EXT_blend_color, EXT_blend_logic_op, EXT_blend_minmax,
> EXT_blend_subtract, EXT_convolution, EXT_copy_texture, EXT_histogram,
> EXT_packed_pixels, EXT_polygon_offset, EXT_subtexture, EXT_texture,
> EXT_texture3D, EXT_texture_object, EXT_vertex_array, SGI_color_matrix,
> SGI_color_table, SGI_texture_color_table, SGIS_texture_filter4,
> SGIX_texture_scale_bias.
> glu version: 1.2 Irix 6.5
> glu extensions (GLU_):
> EXT_abgr, EXT_nurbs_tessellator, EXT_object_space_tess, EXT_packed_pixels,
> EXT_texture, SGI_filter4_parameters.
>
> visual x bf lv rg d st r g b a ax dp st accum buffs ms
> id dep cl sp sz l ci b ro sz sz sz sz bf th cl r g b a ns b
> -----------------------------------------------------------------
> 0x20 8 pc . 8 . c . . . . . . . 24 8 . . . . . .
> 0x21 8 pc . 8 . c . . . . . . . . . . . . . . .
> 0x23 8 pc y 8 1 c . . . . . . . . . . . . . . .
> 0x24 8 pc . 8 1 c . . . . . . . . . . . . . . .
> 0x25 12 pc . 12 . b . . 12 . . . . 24 8 . . . . . .
> 0x26 12 pc . 12 . b . . 12 . . . . . . . . . . . .
> 0x27 12 pc . 12 . b y . 12 . . . . 24 8 . . . . . .
> 0x28 12 pc . 12 . b y . 12 . . . . . . . . . . . .
> 0x29 12 tc . 16 . r y . 4 4 4 4 . 24 8 16 16 16 16 . .
> 0x2a 12 tc . 16 . r y . 4 4 4 4 . . . 16 16 16 16 . .
> 0x2b 15 tc . 16 . r y . 5 5 5 1 . 24 8 16 16 16 16 . .
> 0x2c 15 tc . 16 . r y . 5 5 5 1 . . . 16 16 16 16 . .
> 0x2d 24 tc . 32 . r . . 8 8 8 8 . 24 8 16 16 16 16 . .
> 0x2e 24 tc . 32 . r . . 8 8 8 8 . . . 16 16 16 16 . .
> 0x2f 24 tc . 36 . r . . 12 12 12 . . 24 8 16 16 16 16 . .
> 0x30 24 tc . 36 . r . . 12 12 12 . . . . 16 16 16 16 . .
>
> Managed (":0.0") 1280x1024
> Product ID 0x2, 1 GE, 1 RE, 0 TRAMs
> MGRAS revision 1, RA revision 0
>
> HQ rev B, GE11 rev B, RE4 rev C, PP1 rev A,
> VC3 rev A, CMAP rev E, Heart rev D
> 19" monitor (id 0x1)
>
> Channel 0:
> Origin = (0,0)
> Video Output: 1280 pixels, 1024 lines, 72.24Hz (1280x1024_72)
>
> The config i specify is RGBA = 8888>1
> In the list there is only one entry of 12121224
>
> Thanks
> Ruediger
>
> --

-- 
Phil Keslin <philk++at++engr.sgi.com>

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