gallium: add bits for clipping points as tris (d3d-style)

OpenGL does whole-point clipping, that is a large point is either fully
clipped or fully unclipped (the latter means it may extend beyond the
viewport as long as the center is inside the viewport). d3d9 (d3d10 has
no large points) however requires points to be clipped after they are
expanded to a rectangle. (Note some IHVs are known to ignore GL rules at
least with some hw/drivers.)
Hence add a rasterizer bit indicating which way points should be clipped
(some drivers probably will always ignore this), and add the draw interaction
this requires. Drivers wanting to support this and using draw must support
large points on their own as draw doesn't implement vp clipping on the
expanded points (it potentially could but the complexity doesn't seem
warranted), and the driver needs to do viewport scissoring on such points.

Conflicts:

	src/gallium/drivers/llvmpipe/lp_context.c
	src/gallium/drivers/llvmpipe/lp_state_derived.c

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/gallium/auxiliary/draw/draw_context.c

@@ -262,6 +262,10 @@ static void update_clip_flags( struct draw_context *draw )
                    draw->rasterizer && draw->rasterizer->depth_clip);
    draw->clip_user = draw->rasterizer &&
                      draw->rasterizer->clip_plane_enable != 0;
+   draw->clip_points_xy = draw->clip_xy &&
+                          (!draw->driver.bypass_clip_points ||
+                          (draw->rasterizer &&
+                          !draw->rasterizer->point_tri_clip));
 }
 
 /**
@@ -287,17 +291,23 @@ void draw_set_rasterizer_state( struct draw_context *draw,
  * Some hardware can turn off clipping altogether - in particular any
  * hardware with a TNL unit can do its own clipping, even if it is
  * relying on the draw module for some other reason.
+ * Setting bypass_clip_points to achieve d3d-style point clipping (the driver
+ * will need to do the "vp scissoring") _requires_ the driver to implement
+ * wide points / point sprites itself (points will still be clipped if rasterizer
+ * point_tri_clip isn't set). Only relevant if bypass_clip_xy isn't set.
  */
 void draw_set_driver_clipping( struct draw_context *draw,
                                boolean bypass_clip_xy,
                                boolean bypass_clip_z,
-                               boolean guard_band_xy)
+                               boolean guard_band_xy,
+                               boolean bypass_clip_points)
 {
    draw_do_flush( draw, DRAW_FLUSH_STATE_CHANGE );
 
    draw->driver.bypass_clip_xy = bypass_clip_xy;
    draw->driver.bypass_clip_z = bypass_clip_z;
    draw->driver.guard_band_xy = guard_band_xy;
+   draw->driver.bypass_clip_points = bypass_clip_points;
    update_clip_flags(draw);
 }
 

src/gallium/auxiliary/draw/draw_context.h

@@ -263,7 +263,8 @@ void draw_set_render( struct draw_context *draw,
 void draw_set_driver_clipping( struct draw_context *draw,
                                boolean bypass_clip_xy,
                                boolean bypass_clip_z,
-                               boolean guard_band_xy);
+                               boolean guard_band_xy,
+                               boolean bypass_clip_points);
 
 void draw_set_force_passthrough( struct draw_context *draw, 
                                  boolean enable );

src/gallium/auxiliary/draw/draw_pipe_clip.c

@@ -615,6 +615,31 @@ clip_point( struct draw_stage *stage,
       stage->next->point( stage->next, header );
 }
 
+/*
+ * Clip points but ignore the first 4 (xy) clip planes.
+ * (This is necessary because we don't generate a different shader variant
+ * just for points hence xy clip bits are still generated. This is not really
+ * optimal because of the extra calculations both in generating clip masks
+ * and executing the clip stage but it gets the job done.)
+ */
+static void
+clip_point_no_xy( struct draw_stage *stage,
+                  struct prim_header *header )
+{
+   if ((header->v[0]->clipmask & 0xfffffff0) == 0)
+      stage->next->point( stage->next, header );
+}
+
+
+
+static void
+clip_first_point( struct draw_stage *stage,
+                  struct prim_header *header )
+{
+   stage->point = stage->draw->clip_points_xy ? clip_point : clip_point_no_xy;
+   stage->point(stage, header);
+}
+
 
 static void
 clip_line( struct draw_stage *stage,
@@ -822,7 +847,7 @@ struct draw_stage *draw_clip_stage( struct draw_context *draw )
 
    clipper->stage.draw = draw;
    clipper->stage.name = "clipper";
-   clipper->stage.point = clip_point;
+   clipper->stage.point = clip_first_point;
    clipper->stage.line = clip_first_line;
    clipper->stage.tri = clip_first_tri;
    clipper->stage.flush = clip_flush;

src/gallium/auxiliary/draw/draw_private.h

@@ -217,6 +217,7 @@ struct draw_context
       boolean bypass_clip_xy;
       boolean bypass_clip_z;
       boolean guard_band_xy;
+      boolean bypass_clip_points;
    } driver;
 
    boolean quads_always_flatshade_last;
@@ -231,6 +232,7 @@ struct draw_context
    boolean clip_z;
    boolean clip_user;
    boolean guard_band_xy;
+   boolean clip_points_xy;
 
    boolean force_passthrough; /**< never clip or shade */
 

src/gallium/auxiliary/draw/draw_pt_fetch_shade_pipeline.c

@@ -104,7 +104,8 @@ static void fetch_pipeline_prepare( struct draw_pt_middle_end *middle,
                           fpme->vertex_size,
                           instance_id_index );
    draw_pt_post_vs_prepare( fpme->post_vs,
-                            draw->clip_xy,
+                            gs_out_prim == PIPE_PRIM_POINTS ?
+                                           draw->clip_points_xy : draw->clip_xy,
                             draw->clip_z,
                             draw->clip_user,
                             draw->guard_band_xy,

src/gallium/auxiliary/draw/draw_pt_fetch_shade_pipeline_llvm.c

@@ -155,7 +155,8 @@ llvm_middle_end_prepare( struct draw_pt_middle_end *middle,
 
 
    draw_pt_post_vs_prepare( fpme->post_vs,
-                            draw->clip_xy,
+                            out_prim == PIPE_PRIM_POINTS ?
+                                        draw->clip_points_xy : draw->clip_xy,
                             draw->clip_z,
                             draw->clip_user,
                             draw->guard_band_xy,

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

@@ -200,10 +200,11 @@ point_quad_rasterization
 Determines if points should be rasterized according to quad or point
 rasterization rules.
 
-OpenGL actually has quite different rasterization rules for points and
-point sprites - hence this indicates if points should be rasterized as
-points or according to point sprite (which decomposes them into quads,
-basically) rules.
+(Legacy-only) OpenGL actually has quite different rasterization rules
+for points and point sprites - hence this indicates if points should be
+rasterized as points or according to point sprite (which decomposes them
+into quads, basically) rules. Newer GL versions no longer support the old
+point rules at all.
 
 Additionally Direct3D will always use quad rasterization rules for
 points, regardless of whether point sprites are enabled or not.
@@ -217,6 +218,12 @@ generated.
    Some renderers always internally translate points into quads; this state
    still affects those renderers by overriding other rasterization state.
 
+point_tri_clip
+    Determines if clipping of points should happen after they are converted
+    to "rectangles" (required by d3d) or before (required by OpenGL, though
+    this rule is ignored by some IHVs).
+    It is not valid to set this to enabled but have point_quad_rasterization
+    disabled.
 point_smooth
     Whether points should be smoothed. Point smoothing turns rectangular
     points into circles or ovals.

src/gallium/drivers/svga/svga_swtnl_draw.c

@@ -183,7 +183,7 @@ boolean svga_init_swtnl( struct svga_context *svga )
                                  screen->maxLineWidthAA));
 
    if (debug_get_bool_option("SVGA_SWTNL_FSE", FALSE))
-      draw_set_driver_clipping(svga->swtnl.draw, TRUE, TRUE, TRUE);
+      draw_set_driver_clipping(svga->swtnl.draw, TRUE, TRUE, TRUE, FALSE);
 
    return TRUE;
 

src/gallium/include/pipe/p_state.h

@@ -99,6 +99,7 @@ struct pipe_rasterizer_state
    unsigned point_smooth:1;
    unsigned sprite_coord_mode:1;     /**< PIPE_SPRITE_COORD_ */
    unsigned point_quad_rasterization:1; /** points rasterized as quads or points */
+   unsigned point_tri_clip:1; /** large points clipped as tris or points */
    unsigned point_size_per_vertex:1; /**< size computed in vertex shader */
    unsigned multisample:1;         /* XXX maybe more ms state in future */
    unsigned line_smooth:1;