gallium: implement clamping controls (ARB_color_buffer_float)

BTW this changes the gallium interface.
Some rather cosmetic changes by Marek.

Squashed commit of the following:

commit 513b37d484f0318311e84bb86ed4c93cdff71f13
Author: Luca Barbieri <[email protected]>
Date:   Thu Aug 26 18:17:54 2010 +0200

    mesa/st: respect fragment clamping in st_DrawPixels

commit 546a31e42cad459d7a7a10ebf77fc5ffcf89e9b8
Author: Luca Barbieri <[email protected]>
Date:   Thu Aug 26 18:17:28 2010 +0200

    mesa/st: support fragment and vertex color clamping

commit c406514a1fbee6891da4cf9ac3eebe4e4407ec13
Author: Luca Barbieri <[email protected]>
Date:   Tue Aug 24 21:56:37 2010 +0200

    mesa/st: expose ARB_color_buffer_float if unclamping is supported

commit d0c5ea11b6f75f3da2f4ca989115f150ebc7cf8d
Author: Luca Barbieri <[email protected]>
Date:   Thu Aug 26 17:53:41 2010 +0200

    mesa/st: use unclamped colors

    This assumes that Gallium is to be interpreted as given drivers the
    responsibility to clamp these colors if necessary.

commit aef5c3c6be6edd076e955e37c80905bc447f8a82
Author: Luca Barbieri <[email protected]>
Date:   Thu Aug 26 18:12:34 2010 +0200

    mesa, mesa/st: handle read color clamping properly

    We set IMAGE_CLAMP_BIT in the caller based on _ClampReadColor, where
    the operation mandates it. (see the removed XXX comment. -Marek)

    TODO: did I get the set of operations mandating it right?

commit 76bdfcfe3ff4145a1818e6cb6e227b730a5f12d8
Author: Luca Barbieri <[email protected]>
Date:   Thu Aug 26 18:18:25 2010 +0200

    gallium: add color clamping to the interface

3 files changed, 28 insertions, 0 deletions

diff --git a/src/gallium/docs/source/cso/rasterizer.rst b/src/gallium/docs/source/cso/rasterizer.rst
index d547055096f..e10c16ed900 100644
--- a/src/gallium/docs/source/cso/rasterizer.rst
+++ b/src/gallium/docs/source/cso/rasterizer.rst
@@ -7,6 +7,30 @@ The rasterizer state controls the rendering of points, lines and triangles.
 Attributes include polygon culling state, line width, line stipple,
 multisample state, scissoring and flat/smooth shading.
 
+Linkage
+
+clamp_vertex_color
+^^^^^^^^^^^^^^^^^^
+
+If set, TGSI_SEMANTIC_COLOR registers are clamped to the [0, 1] range after
+the execution of the vertex shader, before being passed to the geometry
+shader or fragment shader.
+
+OpenGL: glClampColor(GL_CLAMP_VERTEX_COLOR) in GL 3.0 or GL_ARB_color_buffer_float
+
+D3D11: seems always disabled
+
+clamp_fragment_color
+^^^^^^^^^^^^^^^^^^^^
+
+Controls whether TGSI_SEMANTIC_COLOR outputs of the fragment shader
+are clamped to [0, 1].
+
+OpenGL: glClampColor(GL_CLAMP_FRAGMENT_COLOR) in GL 3.0 or ARB_color_buffer_float
+
+D3D11: seems always disabled
+
+
 Shading
 -------
 
diff --git a/src/gallium/include/pipe/p_defines.h b/src/gallium/include/pipe/p_defines.h
index bac3300df3c..4f6daa86a59 100644
--- a/src/gallium/include/pipe/p_defines.h
+++ b/src/gallium/include/pipe/p_defines.h
@@ -463,6 +463,8 @@ enum pipe_cap {
    PIPE_CAP_SHADER_STENCIL_EXPORT,
    PIPE_CAP_TGSI_INSTANCEID,
    PIPE_CAP_VERTEX_ELEMENT_INSTANCE_DIVISOR,
+   PIPE_CAP_VERTEX_COLOR_CLAMP_CONTROL,
+   PIPE_CAP_FRAGMENT_COLOR_CLAMP_CONTROL
 };
 
 /* Shader caps not specific to any single stage */
diff --git a/src/gallium/include/pipe/p_state.h b/src/gallium/include/pipe/p_state.h
index cf6c5b50268..f6ad4560f16 100644
--- a/src/gallium/include/pipe/p_state.h
+++ b/src/gallium/include/pipe/p_state.h
@@ -81,6 +81,8 @@ struct pipe_rasterizer_state
 {
    unsigned flatshade:1;
    unsigned light_twoside:1;
+   unsigned clamp_vertex_color:1;
+   unsigned clamp_fragment_color:1;
    unsigned front_ccw:1;
    unsigned cull_face:2;      /**< PIPE_FACE_x */
    unsigned fill_front:2;     /**< PIPE_POLYGON_MODE_x */