st/mesa: add EXT_polygon_offset_clamp support

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Glenn Kennard <glenn.kennard@gmail.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>

docs/relnotes/10.5.0.html

@@ -47,7 +47,7 @@ Note: some of the new features are only available with certain drivers.
 <li>GL_ARB_framebuffer_sRGB on freedreno</li>
 <li>GL_ARB_texture_rg on freedreno</li>
 <li>GL_EXT_packed_float on freedreno</li>
-<li>GL_EXT_polygon_offset_clamp on i965</li>
+<li>GL_EXT_polygon_offset_clamp on i965, nv50, nvc0, r600, radeonsi, llvmpipe</li>
 <li>GL_EXT_texture_shared_exponent on freedreno</li>
 <li>GL_EXT_texture_snorm on freedreno</li>
 </ul>

src/mesa/state_tracker/st_atom_rasterizer.c

@@ -155,6 +155,7 @@ static void update_raster_state( struct st_context *st )
       raster->offset_tri = ctx->Polygon.OffsetFill;
       raster->offset_units = ctx->Polygon.OffsetUnits;
       raster->offset_scale = ctx->Polygon.OffsetFactor;
+      raster->offset_clamp = ctx->Polygon.OffsetClamp;
    }
 
    raster->poly_smooth = ctx->Polygon.SmoothFlag;

src/mesa/state_tracker/st_extensions.c

@@ -464,6 +464,7 @@ void st_init_extensions(struct pipe_screen *screen,
       { o(ARB_conditional_render_inverted),  PIPE_CAP_CONDITIONAL_RENDER_INVERTED      },
       { o(ARB_texture_view),                 PIPE_CAP_SAMPLER_VIEW_TARGET              },
       { o(ARB_clip_control),                 PIPE_CAP_CLIP_HALFZ                       },
+      { o(EXT_polygon_offset_clamp),         PIPE_CAP_POLYGON_OFFSET_CLAMP             },
    };
 
    /* Required: render target and sampler support */