Bug 35425 - Instanced drawing: not implemented
Summary: Instanced drawing: not implemented
Alias: None
Product: Mesa
Classification: Unclassified
Component: Mesa core (show other bugs)
Version: git
Hardware: x86-64 (AMD64) Linux (All)
: medium enhancement
Assignee: mesa-dev
QA Contact:
Depends on:
Reported: 2011-03-18 09:26 UTC by s3734770
Modified: 2011-04-11 10:11 UTC (History)
0 users

See Also:
i915 platform:
i915 features:

Probable patch (2.10 KB, patch)
2011-04-07 01:56 UTC, s3734770
Details | Splinter Review

Description s3734770 2011-03-18 09:26:02 UTC
The follwing output is from the Unigine Heaven Demo:

0:171(53): error: `gl_InstanceID' undeclared
0:171(76): error: Operands to arithmetic operators must be numeric
0:171(76): error: Operands to arithmetic operators must be numeric
0:199(39): error: `gl_InstanceID' undeclared
0:199(42): error: Operands to arithmetic operators must be numeric
0:199(19): error: cannot construct `ivec3' from a non-numeric data type
0:199(58): error: Operands to arithmetic operators must be numeric
GLShader::loadVertex(): error in "core/shaders/meshes/vertex_base.shader" file

(This also occurs on software rendering)

I know that instancing is not implemented in mesa yet. Can you please start designing the interface for mesa/gallium's drivers to enable starting to write the drivers for it?
Comment 1 s3734770 2011-04-07 01:12:01 UTC
The PipeCap for instanced drawing is available, the drivers implement them, TGSI has the construct TGSI_SEMANTIC_INSTANCEID.

The only component that does not support instanced drawing is the GLSL compiler.

So can please any of the GLSL guys implement the gl_InstanceID uniform?
Comment 2 s3734770 2011-04-07 01:56:16 UTC
Created attachment 45367 [details] [review]
Probable patch

This patch works for me, but i dont know if it fits the coding style, so take the best bytes of it to fix the problem
Comment 3 Ian Romanick 2011-04-07 12:57:06 UTC
The application is *BROKEN*.  gl_InstanceID is *NOT* part of GL_ARB_draw_instanced.  The correct name is gl_InstanceIDARB.  Look at the spec (http://www.opengl.org/registry/specs/ARB/draw_instanced.txt).  I'm not going to deviate from the spec to work around broken apps.

The name gl_InstanceID comes from either GLSL 1.40 or GL_EXT_gpu_shader4.  We don't support either of those.  The GL_EXT_draw_instanced spec even mentions this:

  (1) Should instanceID be provided by this extension, or should it be
      provided by EXT_gpu_shader4, thus creating a dependence on that

        Resolved: While this extension could stand alone, its utility
        would be limited without the additional functionality provided
        by EXT_gpu_shader4; also, the spec language is cleaner if
        EXT_gpu_shader4 assumes instanceID is always available, even
        if its value is always zero without this extension.

I already NAKed this patch when it was posted to the mailing list.  See http://marc.info/?l=mesa3d-dev&m=130014281021091&w=2.  Here's what I said there:

NAK for a couple reasons.

This extension depends on EXT_gpu_shader4, which we don't support.
There's no #extension bit required for this extension because the GLSL
changes are implemented by EXT_gpu_shader4.  Without EXT_draw_instanced,
gl_InstanceID always reads 0.

Note that EXT_gpu_shader4 says that a #extension line is required to use
the features of the extension, including gl_InstanceID.  If their driver
allows gl_InstanceID without a #extension line, it is a bug in their driver.

If OilRush is trying to use EXT_gpu_shader4 features without enabling
EXT_gpu_shader4 (or at least checking for the extension!) or using GLSL
1.30, it's a bug in OilRush.

In addition, this patch enables gl_InstanceID even if the driver doesn't
support it.
Comment 4 Marek Olšák 2011-04-07 13:13:46 UTC
(In reply to comment #3)
> The application is *BROKEN*.  gl_InstanceID is *NOT* part of
> GL_ARB_draw_instanced.  The correct name is gl_InstanceIDARB.

Due to this, it would be safer not to advertise ARB_draw_instanced without EXT_gpu_shader4. I haven't seen an app that uses gl_InstanceIDARB when it should. All apps based on Unigine Engine check for ARB_draw_instanced and use gl_InstanceID.

It's pointless to follow the GL spec if no app follows it either.

My 2 eurocents.
Comment 5 s3734770 2011-04-08 08:46:07 UTC
I also share Marek Olšáks opinion.
The mesa driver is ment to be a 3D driver to play games and use 3D application and not to implement a paper-standard.
Just imagine what would happen if browsers would stop parsing if the document would not follow the strict XHTML 1.0 rules. Would you use such a browser?
Comment 6 Ian Romanick 2011-04-08 08:48:52 UTC
Your opinion is noted.
Comment 7 Ian Romanick 2011-04-08 12:28:20 UTC
The GL_ARB_draw_instanced spec is really broken.  In various ways, it does not match what any vendor ships.  The ARB is working on fixing the spec to match a subset of reality that is useful to developers.  Once consensus is reached, there will almost certainly be changes required to Mesa.

Here's a table of the known problems:

                                             AMD   Mesa   NVIDIA
gl_InstanceIDARB must be available         | yes | yes  |  NO
gl_InstanceID must not be available        | NO  | yes  |  NO
Neither can be available if OpenGL 3.0 nor | N/A |  NO  |  N/A
GL_EXT_gpu_shader4 are not supported       |     |      |

I'll reopen this bug once the spec issues are resolved.  My guess is that gl_InstanceID will be added and the GL 3.0 / GL_EXT_gpu_shader4 dependency will be dropped.  It is also possible that, alas, gl_InstanceIDARB will be removed too.  We'll see what happens.
Comment 8 s3734770 2011-04-11 10:11:33 UTC
You could apply the patch with the commit text "started implementing EXT_gpu_shader4 in GLSL: gl_InstanceID" (with some compatibility checks of course)

Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.