gallium: add a flag to turn on gl rasterization rules

Use this to set up hardware rasterization (if your hardware can
do it) or otherwise turn on various tweaks in the draw module.

Currently only hooked up to point biasing code.

src/gallium/auxiliary/draw/draw_wide_point.c

@@ -41,6 +41,9 @@ struct widepoint_stage {
    float point_size_min;
    float point_size_max;
 
+   float xbias;
+   float ybias;
+
    uint texcoord_slot[PIPE_MAX_SHADER_OUTPUTS];
    uint texcoord_mode[PIPE_MAX_SHADER_OUTPUTS];
    uint num_texcoords;
@@ -126,8 +129,6 @@ static void widepoint_point( struct draw_stage *stage,
    float *pos2 = v2->data[0];
    float *pos3 = v3->data[0];
 
-   const float xbias = 0.0, ybias = -0.125;
-
    /* point size is either per-vertex or fixed size */
    if (wide->psize_slot >= 0) {
       half_size = header->v[0]->data[wide->psize_slot][0];
@@ -144,10 +145,10 @@ static void widepoint_point( struct draw_stage *stage,
       half_size = wide->half_point_size;
    }
 
-   left_adj = -half_size + xbias;
-   right_adj = half_size + xbias;
-   bot_adj = half_size + ybias;
-   top_adj = -half_size + ybias;
+   left_adj = -half_size + wide->xbias;
+   right_adj = half_size + wide->xbias;
+   bot_adj = half_size + wide->ybias;
+   top_adj = -half_size + wide->ybias;
 
    pos0[0] += left_adj;
    pos0[1] += top_adj;
@@ -194,6 +195,12 @@ static void widepoint_first_point( struct draw_stage *stage,
    wide->half_point_size = 0.5f * draw->rasterizer->point_size;
    wide->point_size_min = draw->rasterizer->point_size_min;
    wide->point_size_max = draw->rasterizer->point_size_max;
+   wide->xbias = 0.0;
+   wide->ybias = 0.0;
+
+   if (draw->rasterizer->gl_rasterization_rules) {
+      wide->ybias = -0.125;
+   }
 
    /* XXX we won't know the real size if it's computed by the vertex shader! */
    if ((draw->rasterizer->point_size > draw->wide_point_threshold) ||

src/gallium/include/pipe/p_state.h

@@ -115,6 +115,7 @@ struct pipe_rasterizer_state
                             still needed though, to indicate inputs/outputs */
    unsigned origin_lower_left:1;  /**< Is (0,0) the lower-left corner? */
    unsigned flatshade_first:1;   /**< take color attribute from the first vertex of a primitive */
+   unsigned gl_rasterization_rules:1; /**< enable tweaks for GL rasterization?  */
 
    float line_width;
    float point_size;           /**< used when no per-vertex size */

src/mesa/state_tracker/st_atom_rasterizer.c

@@ -261,6 +261,8 @@ static void update_raster_state( struct st_context *st )
    if (ctx->Scissor.Enabled)
       raster->scissor = 1;
 
+   raster->gl_rasterization_rules = 1;
+
    cso_set_rasterizer(st->cso_context, raster);
 }