gallium: add polygon offset clamp state

This is required for D3D1x and supported by hardware.

src/gallium/auxiliary/draw/draw_pipe_offset.c

@@ -43,6 +43,7 @@ struct offset_stage {
 
    float scale;
    float units;
+   float clamp;
 };
 
 
@@ -90,6 +91,10 @@ static void do_offset_tri( struct draw_stage *stage,
 
    float zoffset = offset->units + MAX2(dzdx, dzdy) * offset->scale;
 
+   if (offset->clamp)
+      zoffset = (offset->clamp < 0.0f) ? MAX2(zoffset, offset->clamp) :
+                                         MIN2(zoffset, offset->clamp);
+
    /*
     * Note: we're applying the offset and clamping per-vertex.
     * Ideally, the offset is applied per-fragment prior to fragment shading.
@@ -125,6 +130,7 @@ static void offset_first_tri( struct draw_stage *stage,
 
    offset->units = (float) (stage->draw->rasterizer->offset_units * stage->draw->mrd);
    offset->scale = stage->draw->rasterizer->offset_scale;
+   offset->clamp = stage->draw->rasterizer->offset_clamp;
 
    stage->tri = offset_tri;
    stage->tri( stage, header );

src/gallium/auxiliary/util/u_dump_state.c

@@ -332,6 +332,7 @@ util_dump_rasterizer_state(struct os_stream *stream, const struct pipe_rasterize
    util_dump_member(stream, float, state, point_size);
    util_dump_member(stream, float, state, offset_units);
    util_dump_member(stream, float, state, offset_scale);
+   util_dump_member(stream, float, state, offset_clamp);
 
    util_dump_struct_end(stream);
 }

src/gallium/docs/source/cso/rasterizer.rst

@@ -119,6 +119,8 @@ offset_units
     Specifies the polygon offset bias
 offset_scale
     Specifies the polygon offset scale
+offset_clamp
+    Upper (if > 0) or lower (if < 0) bound on the polygon offset result
 
 
 

src/gallium/drivers/trace/tr_dump_state.c

@@ -149,6 +149,7 @@ void trace_dump_rasterizer_state(const struct pipe_rasterizer_state *state)
    trace_dump_member(float, state, point_size);
    trace_dump_member(float, state, offset_units);
    trace_dump_member(float, state, offset_scale);
+   trace_dump_member(float, state, offset_clamp);
 
    trace_dump_struct_end();
 }

src/gallium/include/pipe/p_state.h

@@ -130,6 +130,7 @@ struct pipe_rasterizer_state
    float point_size;           /**< used when no per-vertex size */
    float offset_units;
    float offset_scale;
+   float offset_clamp;
 };